Advertisement

Evolutionary biology of human hepatitis viruses

  • Andrea Rasche
    Affiliations
    Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Institute of Virology, 10117 Berlin, Germany

    German Center for Infection Research (DZIF), Germany
    Search for articles by this author
  • Anna-Lena Sander
    Affiliations
    Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Institute of Virology, 10117 Berlin, Germany
    Search for articles by this author
  • Victor Max Corman
    Affiliations
    Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Institute of Virology, 10117 Berlin, Germany

    German Center for Infection Research (DZIF), Germany
    Search for articles by this author
  • Jan Felix Drexler
    Correspondence
    Corresponding author. Address: Helmut-Ruska-Haus, Institute of Virology, Campus Charité Mitte, Charitéplatz 1, 10098 Berlin, Germany, Tel.: +49 30 450 625461/Fax: +49 30 450 7525907.
    Affiliations
    Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Institute of Virology, 10117 Berlin, Germany

    German Center for Infection Research (DZIF), Germany
    Search for articles by this author
Published:November 22, 2018DOI:https://doi.org/10.1016/j.jhep.2018.11.010

      Summary

      Hepatitis viruses are major threats to human health. During the last decade, highly diverse viruses related to human hepatitis viruses were found in animals other than primates. Herein, we describe both surprising conservation and striking differences of the unique biological properties and infection patterns of human hepatitis viruses and their animal homologues, including transmission routes, liver tropism, oncogenesis, chronicity, pathogenesis and envelopment. We discuss the potential for translation of newly discovered hepatitis viruses into preclinical animal models for drug testing, studies on pathogenesis and vaccine development. Finally, we re-evaluate the evolutionary origins of human hepatitis viruses and discuss the past and present zoonotic potential of their animal homologues.

      Graphical abstract

      Keywords

      Introduction

      Approximately 1.3 million people die annually from viral hepatitis worldwide. These deaths are predominantly associated with cirrhosis and hepatocellular carcinoma (HCC) resulting from chronic infections with hepatitis B virus (HBV; 887,000 deaths) and hepatitis C virus (HCV; 399,000 deaths), as well as hepatitis and liver failure resulting from acute infections with hepatitis A virus (HAV; 11,000 deaths) and hepatitis E virus (HEV; 44,000 deaths). Worldwide, approximately 5% of people infected with HBV are simultaneously infected with hepatitis delta virus (HDV).
      • Romeo R.
      • Del Ninno E.
      • Rumi M.
      • Russo A.
      • Sangiovanni A.
      • de Franchis R.
      • et al.
      A 28-year study of the course of hepatitis Delta infection: a risk factor for cirrhosis and hepatocellular carcinoma.
      Human hepatitis viruses have ancient zoonotic origins.
      The recent discoveries of novel hepatitis viruses from animals allow revisiting the enigmatic evolutionary origins of human hepatitis viruses. In chapter 1 of this review, we discuss the diverse animal homologues of all human hepatitis viruses that were discovered over the last decades. In chapter 2, we analyse hepatitis virus evolution based on the unique genomic and morphologic properties of human and non-human hepatitis viruses. In chapter 3, we discuss the level of evolutionary conservation of the characteristic infection patterns of human hepatitis viruses and review the ability to translate the recent virus discoveries into tractable animal models. Finally, in chapter 4, we discuss the evolutionary origins of human hepatitis viruses in the context of a plethora of newly discovered animal homologues. In this chapter, we also evaluate the potential of animal homologues for past and present cross-species transmission and compare macro-evolutionary patterns of the different hepatitis virus families.

      Chapter 1: Milestones towards the understanding of the evolutionary origins of hepatitis viruses

      In the following section, we outline the path towards the discovery of human hepatitis viruses and provide detail on the huge expansion in the number of animal homologues discovered during the last decade.

      The discovery of human hepatitis viruses

      The path towards the discovery of human hepatitis viruses started with the differentiation between 2 forms of transmissible jaundice. Infectious hepatitis linked to epidemic outbreaks of faecal-orally transmitted jaundice (termed hepatitis A) was differentiated from a parenterally transmitted jaundice with a relatively longer incubation period (termed hepatitis B).
      • Krugman S.
      • Giles J.P.
      • Hammond J.
      Infectious hepatitis. Evidence for two distinctive clinical, epidemiological, and immunological types of infection.
      • Maccallum F.O.
      Homologous serum hepatitis.
      Following the discoveries of the causative HAV and HBV in 1973 and 1970,
      • Feinstone S.M.
      • Kapikian A.Z.
      • Purceli R.H.
      Hepatitis A: detection by immune electron microscopy of a viruslike antigen associated with acute illness.
      • Dane D.S.
      • Cameron C.H.
      • Briggs M.
      Virus-like particles in serum of patients with Australia-antigen-associated hepatitis.
      the HBV-associated HDV was discovered in 1980.
      • Rizzetto M.
      • Canese M.G.
      • Gerin J.L.
      • London W.T.
      • Sly D.L.
      • Purcell R.H.
      Transmission of the hepatitis B virus-associated delta antigen to chimpanzees.
      In parallel, it was noted that most cases of post-transfusion hepatitis were neither linked to infection with HAV, nor HBV.
      • Feinstone S.M.
      • Kapikian A.Z.
      • Purcell R.H.
      • Alter H.J.
      • Holland P.V.
      Transfusion-associated hepatitis not due to viral hepatitis type A or B.
      However, it was not until 1989 that the causative HCV was finally described.
      • Choo Q.L.
      • Kuo G.
      • Weiner A.J.
      • Overby L.R.
      • Bradley D.W.
      • Houghton M.
      Isolation of a cDNA clone derived from a blood-borne non-A, non-B viral hepatitis genome.
      HEV was discovered in 1983 as the cause of a predominantly water-borne acute non-A, non-B hepatitis.
      • Balayan M.S.
      • Andjaparidze A.G.
      • Savinskaya S.S.
      • Ketiladze E.S.
      • Braginsky D.M.
      • Savinov A.P.
      • et al.
      Evidence for a virus in non-A, non-B hepatitis transmitted via the fecal-oral route.
      The discoveries of human hepatitis viruses were followed by milestones of major clinical relevance, including tools for reliable diagnosis (e.g., described in
      • Drosten C.
      • Weber M.
      • Seifried E.
      • Roth W.K.
      Evaluation of a new PCR assay with competitive internal control sequence for blood donor screening.
      • Drexler J.F.
      • Kupfer B.
      • Petersen N.
      • Grotto R.M.
      • Rodrigues S.M.
      • Grywna K.
      • et al.
      A novel diagnostic target in the hepatitis C virus genome.
      ), the development of direct-acting antiviral treatments against HCV and preventive vaccinations against HAV and HBV
      • Chung R.T.
      • Baumert T.F.
      Curing chronic hepatitis C–the arc of a medical triumph.
      (Fig. 1). Notably, scientific progress was not evenly distributed among human hepatitis viruses. The clinical relevance of HBV and HCV likely contributed to the enormous achievements attained continuously for these 2 viruses (Fig. 1).
      Figure thumbnail gr1
      Fig. 1Selected milestones in hepatitis virus research. References include for HAV,
      • Feinstone S.M.
      • Kapikian A.Z.
      • Purceli R.H.
      Hepatitis A: detection by immune electron microscopy of a viruslike antigen associated with acute illness.
      • Nainan O.V.
      • Margolis H.S.
      • Robertson B.H.
      • Balayan M.
      • Brinton M.A.
      Sequence analysis of a new hepatitis A virus naturally infecting cynomolgus macaques (Macaca fascicularis).
      • Drexler J.F.
      • Corman V.M.
      • Lukashev A.N.
      • van den Brand J.M.
      • Gmyl A.P.
      • Brunink S.
      • et al.
      Evolutionary origins of hepatitis A virus in small mammals.
      • Anthony S.J.
      • St Leger J.A.
      • Liang E.
      • Hicks A.L.
      • Sanchez-Leon M.D.
      • Jain K.
      • et al.
      Discovery of a novel hepatovirus (phopivirus of seals) related to human hepatitis.
      • de Oliveira Carneiro I
      • Sander A.L.
      • Silva N.
      • Moreira-Soto A.
      • Normann A.
      • Flehmig B.
      • et al.
      A novel marsupial hepatitis A virus corroborates complex evolutionary patterns shaping the genus Hepatovirus.
      • Feng Z.
      • Hensley L.
      • McKnight K.L.
      • Hu F.
      • Madden V.
      • Ping L.
      • et al.
      A pathogenic picornavirus acquires an envelope by hijacking cellular membranes.
      • Dienstag J.L.
      • Feinstone S.M.
      • Purcell R.H.
      • Hoofnagle J.H.
      • Barker L.F.
      • London W.T.
      • et al.
      Experimental infection of chimpanzees with hepatitis A virus.
      • Provost P.J.
      • Hilleman M.R.
      Propagation of human hepatitis A virus in cell culture in vitro.
      • Najarian R.
      • Caput D.
      • Gee W.
      • Potter S.J.
      • Renard A.
      • Merryweather J.
      • et al.
      Primary structure and gene organization of human hepatitis A virus.
      • Mao J.S.
      • Dong D.X.
      • Zhang H.Y.
      • Chen N.L.
      • Zhang X.Y.
      • Huang H.Y.
      • et al.
      Primary study of attenuated live hepatitis A vaccine (H2 strain) in humans.
      for HBV,
      • Dane D.S.
      • Cameron C.H.
      • Briggs M.
      Virus-like particles in serum of patients with Australia-antigen-associated hepatitis.
      • Drexler J.F.
      • Geipel A.
      • Konig A.
      • Corman V.M.
      • van Riel D.
      • Leijten L.M.
      • et al.
      • Yan H.
      • Zhong G.
      • Xu G.
      • He W.
      • Jing Z.
      • Gao Z.
      • et al.
      Sodium taurocholate cotransporting polypeptide is a functional receptor for human hepatitis B and D virus.
      • Summers J.
      • Smolec J.M.
      • Snyder R.
      • Mason W.S.
      • Seal G.
      • Summers J.
      Virus of Pekin ducks with structural and biological relatedness to human hepatitis B virus.
      • Lanford R.E.
      • Chavez D.
      • Brasky K.M.
      • Burns 3rd, R.B.
      • Vaudin M.
      • Wolstenholme A.J.
      • Tsiquaye K.N.
      • Zuckerman A.J.
      • Harrison T.J.
      The complete nucleotide sequence of the genome of a hepatitis B virus isolated from a naturally infected chimpanzee.
      • Aghazadeh M.
      • Shi M.
      • Barrs V.R.
      • McLuckie A.
      • Lindsay S.
      • Jameson B.
      • et al.
      A novel hepadnavirus identified in an immunocompromised domestic cat in Australia.
      • de Carvalho Dominguez Souza B.F.
      • Konig A.
      • Rasche A.
      • de Oliveira Carneiro I.
      • Stephan N.
      • Corman V.M.
      • et al.
      A novel hepatitis B virus species discovered in capuchin monkeys sheds new light on the evolution of primate hepadnaviruses.
      • Dill J.A.
      • Camus A.C.
      • Leary J.H.
      • Di Giallonardo F.
      • Holmes E.C.
      • Ng T.F.
      Distinct viral lineages from fish and amphibians reveal the complex evolutionary history of hepadnaviruses.
      • Hahn C.M.
      • Iwanowicz L.R.
      • Cornman R.S.
      • Conway C.M.
      • Winton J.R.
      • Blazer V.S.
      Characterization of a novel hepadnavirus in the white sucker (Catostomus commersonii) from the Great Lakes Region of the United States.
      • Blumberg B.S.
      • Alter H.J.
      • Visnich S.
      A “new” antigen in leukemia sera.
      • Greenberg H.B.
      • Pollard R.B.
      • Lutwick L.I.
      • Gregory P.B.
      • Robinson W.S.
      • Merigan T.C.
      Effect of human leukocyte interferon on hepatitis B virus infection in patients with chronic active hepatitis.
      • Galibert F.
      • Mandart E.
      • Fitoussi F.
      • Tiollais P.
      • Charnay P.
      Nucleotide sequence of the hepatitis B virus genome (subtype ayw) cloned in E. coli.
      • Szmuness W.
      • Stevens C.E.
      • Harley E.J.
      • Zang E.A.
      • Oleszko W.R.
      • William D.C.
      • et al.
      Hepatitis B vaccine: demonstration of efficacy in a controlled clinical trial in a high-risk population in the United States.
      for HCV,
      • Feinstone S.M.
      • Kapikian A.Z.
      • Purcell R.H.
      • Alter H.J.
      • Holland P.V.
      Transfusion-associated hepatitis not due to viral hepatitis type A or B.
      • Choo Q.L.
      • Kuo G.
      • Weiner A.J.
      • Overby L.R.
      • Bradley D.W.
      • Houghton M.
      Isolation of a cDNA clone derived from a blood-borne non-A, non-B viral hepatitis genome.
      • Simons J.N.
      • Pilot-Matias T.J.
      • Leary T.P.
      • Dawson G.J.
      • Desai S.M.
      • Schlauder G.G.
      • et al.
      • Suh A.
      • Weber C.C.
      • Kehlmaier C.
      • Braun E.L.
      • Green R.E.
      • Fritz U.
      • et al.
      Early mesozoic coexistence of amniotes and hepadnaviridae.
      • Burbelo P.D.
      • Dubovi E.J.
      • Simmonds P.
      • Medina J.L.
      • Henriquez J.A.
      • Mishra N.
      • et al.
      Serology-enabled discovery of genetically diverse hepaciviruses in a new host.
      • Pileri P.
      • Uematsu Y.
      • Campagnoli S.
      • Galli G.
      • Falugi F.
      • Petracca R.
      • et al.
      Binding of hepatitis C virus to CD81.
      • Kapoor A.
      • Simmonds P.
      • Scheel T.K.
      • Hjelle B.
      • Cullen J.M.
      • Burbelo P.D.
      • et al.
      Identification of rodent homologs of hepatitis C virus and pegiviruses.
      • Drexler J.F.
      • Corman V.M.
      • Muller M.A.
      • Lukashev A.N.
      • Gmyl A.
      • Coutard B.
      • et al.
      Evidence for novel hepaciviruses in rodents.
      • Quan P.L.
      • Firth C.
      • Conte J.M.
      • Williams S.H.
      • Zambrana-Torrelio C.M.
      • Anthony S.J.
      • et al.
      Bats are a major natural reservoir for hepaciviruses and pegiviruses.
      • Corman V.M.
      • Grundhoff A.
      • Baechlein C.
      • Fischer N.
      • Gmyl A.
      • Wollny R.
      • et al.
      Highly divergent hepaciviruses from African cattle.
      • Baechlein C.
      • Fischer N.
      • Grundhoff A.
      • Alawi M.
      • Indenbirken D.
      • Postel A.
      • et al.
      Identification of a novel hepacivirus in domestic cattle from Germany.
      • Hoofnagle J.H.
      • Mullen K.D.
      • Jones D.B.
      • Rustgi V.
      • Di Bisceglie A.
      • Peters M.
      • et al.
      Treatment of chronic non-A, non-B hepatitis with recombinant human alpha interferon. A preliminary report.
      • Yanagi M.
      • Purcell R.H.
      • Emerson S.U.
      • Bukh J.
      Transcripts from a single full-length cDNA clone of hepatitis C virus are infectious when directly transfected into the liver of a chimpanzee.
      • Wakita T.
      • Pietschmann T.
      • Kato T.
      • Date T.
      • Miyamoto M.
      • Zhao Z.
      • et al.
      Production of infectious hepatitis C virus in tissue culture from a cloned viral genome.
      • Bacon B.R.
      • Gordon S.C.
      • Lawitz E.
      • Marcellin P.
      • Vierling J.M.
      • Zeuzem S.
      • et al.
      Boceprevir for previously treated chronic HCV genotype 1 infection.
      • Sherman K.E.
      • Flamm S.L.
      • Afdhal N.H.
      • Nelson D.R.
      • Sulkowski M.S.
      • Everson G.T.
      • et al.
      Response-guided telaprevir combination treatment for hepatitis C virus infection.
      for HDV
      • Rizzetto M.
      • Canese M.G.
      • Gerin J.L.
      • London W.T.
      • Sly D.L.
      • Purcell R.H.
      Transmission of the hepatitis B virus-associated delta antigen to chimpanzees.
      • Wille M.
      • Netter H.J.
      • Littlejohn M.
      • Yuen L.
      • Shi M.
      • Eden J.-S.
      • et al.
      A divergent hepatitis D-like agent in birds.
      • Yan H.
      • Zhong G.
      • Xu G.
      • He W.
      • Jing Z.
      • Gao Z.
      • et al.
      Sodium taurocholate cotransporting polypeptide is a functional receptor for human hepatitis B and D virus.
      • Polson A.G.
      • Bass B.L.
      • Casey J.L.
      RNA editing of hepatitis delta virus antigenome by dsRNA-adenosine deaminase.
      • Jopling C.L.
      • Yi M.
      • Lancaster A.M.
      • Lemon S.M.
      • Sarnow P.
      Modulation of hepatitis C virus RNA abundance by a liver-specific MicroRNA.
      • Rizzetto M.
      • Canese M.G.
      • Arico S.
      • Crivelli O.
      • Trepo C.
      • Bonino F.
      • et al.
      Immunofluorescence detection of new antigen-antibody system (delta/anti-delta) associated to hepatitis B virus in liver and in serum of HBsAg carriers.
      • Kos A.
      • Dijkema R.
      • Arnberg A.C.
      • van der Meide P.H.
      • Schellekens H.
      The hepatitis delta (delta) virus possesses a circular RNA.
      • Wang K.S.
      • Choo Q.L.
      • Weiner A.J.
      • Ou J.H.
      • Najarian R.C.
      • Thayer R.M.
      • et al.
      Structure, sequence and expression of the hepatitis delta (delta) viral genome.
      and for HEV.
      • Balayan M.S.
      • Andjaparidze A.G.
      • Savinskaya S.S.
      • Ketiladze E.S.
      • Braginsky D.M.
      • Savinov A.P.
      • et al.
      Evidence for a virus in non-A, non-B hepatitis transmitted via the fecal-oral route.
      • Hetzel U.
      • Szirovicza L.
      • Smura T.
      • Prahauser B.
      • Vapalahti O.
      • Kipar A.
      • et al.
      Identification of a novel deltavirus in Boa constrictor.
      • Zhao C.
      • Ma Z.
      • Harrison T.J.
      • Feng R.
      • Zhang C.
      • Qiao Z.
      • et al.
      A novel genotype of hepatitis E virus prevalent among farmed rabbits in China.
      • Woo P.C.
      • Lau S.K.
      • Teng J.L.
      • Tsang A.K.
      • Joseph M.
      • Wong E.Y.
      • et al.
      New hepatitis E virus genotype in camels, the Middle East.
      • Drexler J.F.
      • Seelen A.
      • Corman V.M.
      • Fumie Tateno A.
      • Cottontail V.
      • Melim Zerbinati R.
      • et al.
      Bats worldwide carry hepatitis E virus-related viruses that form a putative novel genus within the family Hepeviridae.
      • Batts W.
      • Yun S.
      • Hedrick R.
      • Winton J.
      A novel member of the family Hepeviridae from cutthroat trout (Oncorhynchus clarkii).
      • Payne C.J.
      • Ellis T.M.
      • Plant S.L.
      • Gregory A.R.
      • Wilcox G.E.
      Sequence data suggests big liver and spleen disease virus (BLSV) is genetically related to hepatitis E virus.
      • Takahashi M.
      • Tanaka T.
      • Takahashi H.
      • Hoshino Y.
      • Nagashima S.
      • Jirintai
      • et al.
      Hepatitis E Virus (HEV) strains in serum samples can replicate efficiently in cultured cells despite the coexistence of HEV antibodies: characterization of HEV virions in blood circulation.
      • Johne R.
      • Plenge-Bonig A.
      • Hess M.
      • Ulrich R.G.
      • Reetz J.
      • Schielke A.
      Detection of a novel hepatitis E-like virus in faeces of wild rats using a nested broad-spectrum RT-PCR.
      • Khuroo M.S.
      Study of an epidemic of non-A, non-B hepatitis. Possibility of another human hepatitis virus distinct from post-transfusion non-A, non-B type.
      • Reyes G.R.
      • Yarbough P.O.
      • Tam A.W.
      • Purdy M.A.
      • Huang C.C.
      • Kim J.S.
      • et al.
      Hepatitis E virus (HEV): the novel agent responsible for enterically transmitted non-A, non-B hepatitis.
      • Meng X.J.
      • Purcell R.H.
      • Halbur P.G.
      • Lehman J.R.
      • Webb D.M.
      • Tsareva T.S.
      • et al.
      A novel virus in swine is closely related to the human hepatitis E virus.
      • Husain M.M.
      • Aggarwal R.
      • Kumar D.
      • Jameel S.
      • Naik S.
      Effector T cells immune reactivity among patients with acute hepatitis E.
      • Kamar N.
      • Izopet J.
      • Tripon S.
      • Bismuth M.
      • Hillaire S.
      • Dumortier J.
      • et al.
      Ribavirin for chronic hepatitis E virus infection in transplant recipients.
      Due to space constraints, only selected milestones are shown. Animal pictograms represent host orders in which distinct hepatitis viruses were detected. DAA, direct-acting antiviral; HAV, hepatitis A virus; HBV, hepatitis B virus; HCV, hepatitis C virus; HDV, hepatitis delta virus; HEV, hepatitis E virus; miR-122, micro RNA-122; NRTI, nucleoside reverse transcriptase inhibitor; NTCP, sodium taurocholate co-transporting polypeptide; RBV, ribavirin.

      A new era of virus discovery

      The first discoveries of non-human hepatitis viruses were ground breaking, yet sporadic. In 1978, a genetically distant relative of HBV, the woodchuck hepatitis virus (WHV), was identified in American woodchucks, a marmot-like rodent species.
      • Summers J.
      • Smolec J.M.
      • Snyder R.
      The discovery of WHV was followed by the discovery of duck hepatitis B virus (DHBV), HBV variants in apes, and a divergent HBV species termed woolly monkey hepatitis B virus (WMHBV).
      • Mason W.S.
      • Seal G.
      • Summers J.
      Virus of Pekin ducks with structural and biological relatedness to human hepatitis B virus.
      • Lanford R.E.
      • Chavez D.
      • Brasky K.M.
      • Burns 3rd, R.B.
      • Vaudin M.
      • Wolstenholme A.J.
      • Tsiquaye K.N.
      • Zuckerman A.J.
      • Harrison T.J.
      The complete nucleotide sequence of the genome of a hepatitis B virus isolated from a naturally infected chimpanzee.
      For hepatitis viruses other than HBV, knowledge on potential non-human hosts remained scarce. In the 1990s, a distinct HAV type was detected in macaques
      • Nainan O.V.
      • Margolis H.S.
      • Robertson B.H.
      • Balayan M.
      • Brinton M.A.
      Sequence analysis of a new hepatitis A virus naturally infecting cynomolgus macaques (Macaca fascicularis).
      and HEV was recovered from swine.
      • Meng X.J.
      • Halbur P.G.
      • Shapiro M.S.
      • Govindarajan S.
      • Bruna J.D.
      • Mushahwar I.K.
      • et al.
      Genetic and experimental evidence for cross-species infection by swine hepatitis E virus.
      In 1995, a non-human primate (NHP) virus distantly related to HCV, termed GB virus-B (GBV-B) was isolated from a laboratory tamarin.
      • Simons J.N.
      • Pilot-Matias T.J.
      • Leary T.P.
      • Dawson G.J.
      • Desai S.M.
      • Schlauder G.G.
      • et al.
      The tamarin had been inoculated with the serum of a patient with hepatitis, but since GBV-B was never detected in humans, it was most likely a tamarin virus.
      • Robertson B.H.
      Viral hepatitis and primates: historical and molecular analysis of human and nonhuman primate hepatitis A, B, and the GB-related viruses.
      Over the last decades there has been an explosive expansion of the recognized viral diversity in animals, driven by novel sequencing techniques and an unprecedented focus on zoonotic pathogens which followed the identification of highly pathogenic viruses such as Ebola virus and SARS-coronavirus in bats.
      • Leroy E.M.
      • Kumulungui B.
      • Pourrut X.
      • Rouquet P.
      • Hassanin A.
      • Yaba P.
      • et al.
      Fruit bats as reservoirs of Ebola virus.
      • Li W.
      • Shi Z.
      • Yu M.
      • Ren W.
      • Smith C.
      • Epstein J.H.
      • et al.
      Bats are natural reservoirs of SARS-like coronaviruses.
      A plethora of HAV-related viruses were recovered from various mammalian species during 2015–2018, including predominantly bats and rodents, but also tree shrews, seals and marsupials.
      • Drexler J.F.
      • Corman V.M.
      • Lukashev A.N.
      • van den Brand J.M.
      • Gmyl A.P.
      • Brunink S.
      • et al.
      Evolutionary origins of hepatitis A virus in small mammals.
      • Anthony S.J.
      • St Leger J.A.
      • Liang E.
      • Hicks A.L.
      • Sanchez-Leon M.D.
      • Jain K.
      • et al.
      Discovery of a novel hepatovirus (phopivirus of seals) related to human hepatitis.
      • Yu J.M.
      • Li L.L.
      • Zhang C.Y.
      • Lu S.
      • Ao Y.Y.
      • Gao H.C.
      • et al.
      A novel hepatovirus identified in wild woodchuck Marmota himalayana.
      • de Oliveira Carneiro I
      • Sander A.L.
      • Silva N.
      • Moreira-Soto A.
      • Normann A.
      • Flehmig B.
      • et al.
      A novel marsupial hepatitis A virus corroborates complex evolutionary patterns shaping the genus Hepatovirus.
      • Sander A.L.
      • Corman V.M.
      • Lukashev A.N.
      • Drexler J.F.
      Evolutionary Origins of Enteric Hepatitis Viruses.
      HBV-related viruses were detected in bats during 2013–2015
      • Drexler J.F.
      • Geipel A.
      • Konig A.
      • Corman V.M.
      • van Riel D.
      • Leijten L.M.
      • et al.
      • He B.
      • Zhang F.
      • Xia L.
      • Hu T.
      • Chen G.
      • Qiu W.
      • et al.
      Identification of a novel Orthohepadnavirus in pomona roundleaf bats in China.
      and in a domestic cat in 2018.
      • Aghazadeh M.
      • Shi M.
      • Barrs V.R.
      • McLuckie A.
      • Lindsay S.
      • Jameson B.
      • et al.
      A novel hepadnavirus identified in an immunocompromised domestic cat in Australia.
      A distinct HBV species termed capuchin monkey hepatitis B virus (CMHBV) was described in 2018.
      • de Carvalho Dominguez Souza B.F.
      • Konig A.
      • Rasche A.
      • de Oliveira Carneiro I.
      • Stephan N.
      • Corman V.M.
      • et al.
      A novel hepatitis B virus species discovered in capuchin monkeys sheds new light on the evolution of primate hepadnaviruses.
      Endogenous and exogenous viruses distantly related to HBV were detected in reptiles, fish and amphibians.
      • Dill J.A.
      • Camus A.C.
      • Leary J.H.
      • Di Giallonardo F.
      • Holmes E.C.
      • Ng T.F.
      Distinct viral lineages from fish and amphibians reveal the complex evolutionary history of hepadnaviruses.
      • Hahn C.M.
      • Iwanowicz L.R.
      • Cornman R.S.
      • Conway C.M.
      • Winton J.R.
      • Blazer V.S.
      Characterization of a novel hepadnavirus in the white sucker (Catostomus commersonii) from the Great Lakes Region of the United States.
      • Lauber C.
      • Seitz S.
      • Mattei S.
      • Suh A.
      • Beck J.
      • Herstein J.
      • et al.
      Deciphering the origin and evolution of hepatitis B viruses by means of a family of non-enveloped fish viruses.
      • Suh A.
      • Weber C.C.
      • Kehlmaier C.
      • Braun E.L.
      • Green R.E.
      • Fritz U.
      • et al.
      Early mesozoic coexistence of amniotes and hepadnaviridae.
      HCV-related viruses were detected in horses in 2012, and evidence for sporadic spill-over infections of the horse-associated viruses into dogs and donkeys was found.
      • Burbelo P.D.
      • Dubovi E.J.
      • Simmonds P.
      • Medina J.L.
      • Henriquez J.A.
      • Mishra N.
      • et al.
      Serology-enabled discovery of genetically diverse hepaciviruses in a new host.
      • Kapoor A.
      • Simmonds P.
      • Gerold G.
      • Qaisar N.
      • Jain K.
      • Henriquez J.A.
      • et al.
      Characterization of a canine homolog of hepatitis C virus.
      • Lyons S.
      • Kapoor A.
      • Schneider B.S.
      • Wolfe N.D.
      • Culshaw G.
      • Corcoran B.
      • et al.
      Viraemic frequencies and seroprevalence of non-primate hepacivirus and equine pegiviruses in horses and other mammalian species.
      • Walter S.
      • Rasche A.
      • Moreira-Soto A.
      • Pfaender S.
      • Bletsa M.
      • Corman V.M.
      • et al.
      Infection patterns and recent evolutionary origins of equine hepaciviruses in donkeys.
      Soon afterwards, highly diverse HCV-related viruses were detected in bats and rodents,
      • Drexler J.F.
      • Corman V.M.
      • Muller M.A.
      • Lukashev A.N.
      • Gmyl A.
      • Coutard B.
      • et al.
      Evidence for novel hepaciviruses in rodents.
      • Quan P.L.
      • Firth C.
      • Conte J.M.
      • Williams S.H.
      • Zambrana-Torrelio C.M.
      • Anthony S.J.
      • et al.
      Bats are a major natural reservoir for hepaciviruses and pegiviruses.
      in cattle,
      • Corman V.M.
      • Grundhoff A.
      • Baechlein C.
      • Fischer N.
      • Gmyl A.
      • Wollny R.
      • et al.
      Highly divergent hepaciviruses from African cattle.
      • Baechlein C.
      • Fischer N.
      • Grundhoff A.
      • Alawi M.
      • Indenbirken D.
      • Postel A.
      • et al.
      Identification of a novel hepacivirus in domestic cattle from Germany.
      and in black-and-white colobus monkeys.
      • Lauck M.
      • Sibley S.D.
      • Lara J.
      • Purdy M.A.
      • Khudyakov Y.
      • Hyeroba D.
      • et al.
      A novel hepacivirus with an unusually long and intrinsically disordered NS5A protein in a wild Old World primate.
      Hepatitis D-like agents were recently detected in ducks and snakes.
      • Wille M.
      • Netter H.J.
      • Littlejohn M.
      • Yuen L.
      • Shi M.
      • Eden J.-S.
      • et al.
      A divergent hepatitis D-like agent in birds.
      • Hetzel U.
      • Szirovicza L.
      • Smura T.
      • Prahauser B.
      • Vapalahti O.
      • Kipar A.
      • et al.
      Identification of a novel deltavirus in Boa constrictor.
      Zoonotic HEV genotypes were discovered in wild boars, camelids, rabbits and rats.
      • Takahashi M.
      • Nishizawa T.
      • Sato H.
      • Sato Y.
      • Jirintai
      • Nagashima S.
      • et al.
      Analysis of the full-length genome of a hepatitis E virus isolate obtained from a wild boar in Japan that is classifiable into a novel genotype.
      • Zhao C.
      • Ma Z.
      • Harrison T.J.
      • Feng R.
      • Zhang C.
      • Qiao Z.
      • et al.
      A novel genotype of hepatitis E virus prevalent among farmed rabbits in China.
      • Woo P.C.
      • Lau S.K.
      • Teng J.L.
      • Tsang A.K.
      • Joseph M.
      • Wong E.Y.
      • et al.
      New hepatitis E virus genotype in camels, the Middle East.
      • Rasche A.
      • Saqib M.
      • Liljander A.M.
      • Bornstein S.
      • Zohaib A.
      • Renneker S.
      • et al.
      Hepatitis E virus infection in dromedaries, North and East Africa, United Arab Emirates, and Pakistan, 1983–2015.
      • Sridhar S.
      • Yip C.C.Y.
      • Wu S.
      • Cai J.
      • Zhang A.J.
      • Leung K.H.
      • et al.
      Rat Hepatitis E Virus as Cause of Persistent Hepatitis after Liver Transplant.
      In addition, divergent HEV-related viruses were described in bats, ferrets, rodents, birds, and fish.
      • Raj V.S.
      • Smits S.L.
      • Pas S.D.
      • Provacia L.B.
      • Moorman-Roest H.
      • Osterhaus A.D.
      • et al.
      Novel hepatitis E virus in ferrets, the Netherlands.
      • Drexler J.F.
      • Seelen A.
      • Corman V.M.
      • Fumie Tateno A.
      • Cottontail V.
      • Melim Zerbinati R.
      • et al.
      Bats worldwide carry hepatitis E virus-related viruses that form a putative novel genus within the family Hepeviridae.
      • Johne R.
      • Heckel G.
      • Plenge-Bonig A.
      • Kindler E.
      • Maresch C.
      • Reetz J.
      • et al.
      Novel hepatitis E virus genotype in Norway rats, Germany.
      • Batts W.
      • Yun S.
      • Hedrick R.
      • Winton J.
      A novel member of the family Hepeviridae from cutthroat trout (Oncorhynchus clarkii).
      • de Souza W.M.
      • Romeiro M.F.
      • Sabino-Santos Jr., G.
      • Maia F.G.M.
      • Fumagalli M.J.
      • Modha S.
      • et al.
      Novel orthohepeviruses in wild rodents from Sao Paulo State, Brazil.
      • Wang B.
      • Li W.
      • Zhou J.H.
      • Li B.
      • Zhang W.
      • Yang W.H.
      • et al.
      Chevrier’s field mouse (Apodemus chevrieri) and Pere David’s Vole (Eothenomys melanogaster) in China carry orthohepeviruses that form two putative novel genotypes within the species orthohepevirus C.
      • Payne C.J.
      • Ellis T.M.
      • Plant S.L.
      • Gregory A.R.
      • Wilcox G.E.
      Sequence data suggests big liver and spleen disease virus (BLSV) is genetically related to hepatitis E virus.
      In sum, homologues of all human hepatitis viruses exist in diverse animals. Apart from the detection of zoonotic HEV strains, none of the recent studies into viral diversity in animals revealed any direct ancestor of human hepatitis viruses, as outlined below.
      Diverse animals host hepatitis viruses, but ongoing zoonotic transmission is documented only for hepatitis E virus.

      Chapter 2: Conservation and de novo emergence of unique properties of hepatitis viruses

      Human hepatitis viruses are assigned to diverse virus families and genera (Table 1). Namely, they belong to the families Picornaviridae, genus Hepatovirus (HAV), Hepadnaviridae, genus Orthohepadnavirus (HBV), Flaviviridae, genus Hepacivirus (HCV), and Hepeviridae, genus Orthohepevirus (HEV). The genus Deltavirus (HDV) is unassigned to any virus family. In general, human and non-human hepatitis virus homologues resemble each other in major genomic properties such as structure of the genomic nucleic acid, open reading frame (ORF) composition, genome length and presence and type of noncoding regions (Table 1, Fig. 2). Nonetheless, there are striking differences among viruses from the same family or genus. Hypothetically, de novo emergence of genomic features and recombination events during evolution may have contributed to the rise of viruses eventually pathogenic to humans. A prototypic example for micro-evolutionary events within animal reservoirs enabling efficient human infection is the recombination event leading to the functional tetherin antagonist in chimpanzee-associated ancestors of the HIV-1 group M.
      • Sauter D.
      • Schindler M.
      • Specht A.
      • Landford W.N.
      • Munch J.
      • Kim K.A.
      • et al.
      Tetherin-driven adaptation of Vpu and Nef function and the evolution of pandemic and nonpandemic HIV-1 strains.
      Table 1Properties of human hepatitis viruses.
      HAVHBVHCVHDVHEV
      Virus family, genusPicornaviridae, HepatovirusHepadnaviridae,

      Orthohepadnavirus
      Flaviviridae,

      Hepacivirus
      Unassigned, DeltavirusHepeviridae, Orthohepevirus
      Genome typePositive-sense linear ssRNACircular, partially dsDNA (full length negative-sense, partial positive-sense), replication via reverse transcriptionPositive-sense linear ssRNAViroid-like, negative-sense circular ssRNAPositive-sense linear ssRNA
      Approx. genome length (nt)7,5003,2009,6001,7007,200
      Virion diameter (nm)27–324255–6536–4330–34
      EnvelopeNo/quasi-envelopedYesYesYesNo/quasi-enveloped
      Course of infectionAcute
      • Lemon S.M.
      • Ott J.J.
      • Van Damme P.
      • Shouval D.
      Type A viral hepatitis: a summary and update on the molecular virology, epidemiology, pathogenesis and prevention.
      Acute/chronic (children 30–90%; adults <5%)
      • Paganelli M.
      • Stephenne X.
      • Sokal E.M.
      Chronic hepatitis B in children and adolescents.
      Acute/chronic

      (80–85%)
      • Webster D.P.
      • Klenerman P.
      • Dusheiko G.M.
      Hepatitis C.
      Acute/chronic

      (>80% if superinfection)
      • Pascarella S.
      • Negro F.
      Hepatitis D virus: an update.
      Acute/chronic (<1%)
      • Pischke S.
      • Behrendt P.
      • Bock C.T.
      • Jilg W.
      • Manns M.P.
      • Wedemeyer H.
      Hepatitis E in Germany–an under-reported infectious disease.
      Predominant transmission routesMainly faecal-oral, parenteralVertical, parenteral,

      sexual
      ParenteralParenteral, sexualFaecal-oral, food-borne, parenteral
      Cellular receptorUnknown
      • Das A.
      • Hirai-Yuki A.
      • Gonzalez-Lopez O.
      • Rhein B.
      • Moller-Tank S.
      • Brouillette R.
      • et al.
      TIM1 (HAVCR1) is not essential for cellular entry of either quasi-enveloped or naked hepatitis A virions.
      NTCP, heparan sulfate proteoglycans
      • Yan H.
      • Zhong G.
      • Xu G.
      • He W.
      • Jing Z.
      • Gao Z.
      • et al.
      Sodium taurocholate cotransporting polypeptide is a functional receptor for human hepatitis B and D virus.
      • Schulze A.
      • Gripon P.
      • Urban S.
      Hepatitis B virus infection initiates with a large surface protein-dependent binding to heparan sulfate proteoglycans.
      CD81, SR-B1, LDL receptor, claudin-1, occludine
      • Catanese M.T.
      • Ansuini H.
      • Graziani R.
      • Huby T.
      • Moreau M.
      • Ball J.K.
      • et al.
      Role of scavenger receptor class B type I in hepatitis C virus entry: kinetics and molecular determinants.
      • Yamamoto S.
      • Fukuhara T.
      • Ono C.
      • Uemura K.
      • Kawachi Y.
      • Shiokawa M.
      • et al.
      Lipoprotein receptors redundantly participate in entry of hepatitis C virus.
      • Pileri P.
      • Uematsu Y.
      • Campagnoli S.
      • Galli G.
      • Falugi F.
      • Petracca R.
      • et al.
      Binding of hepatitis C virus to CD81.
      NTCP, heparan sulfate proteoglycans
      • Yan H.
      • Zhong G.
      • Xu G.
      • He W.
      • Jing Z.
      • Gao Z.
      • et al.
      Sodium taurocholate cotransporting polypeptide is a functional receptor for human hepatitis B and D virus.
      • Lamas Longarela O.
      • Schmidt T.T.
      • Schoneweis K.
      • Romeo R.
      • Wedemeyer H.
      • Urban S.
      • et al.
      Proteoglycans act as cellular hepatitis delta virus attachment receptors.
      Unknown
      dsDNA, double-stranded DNA; nt, nucleotide; NTCP, sodium taurocholate co-transporting polypeptide; ssRNA, single-stranded RNA.
      Figure thumbnail gr2
      Fig. 2Virus particles and genome characteristics of human hepatitis viruses. C, core protein; CP, capsid protein; E, envelope protein; HAV, hepatitis A virus; HBV, hepatitis B virus; HCV, hepatitis C virus; HDV, hepatitis delta virus; HEV, hepatitis E virus; Hel, Helicase; HVR, hypervariable region; IRES, Internal ribosomal entry site; LHBs, large surface protein; L-HDAg, large hepatitis delta antigen; MHBs, medium surface protein; MeT, methyltransferase; NS, non-structural protein; ORF, open reading frame; PCP, papain-like cysteine protease; Pol, polymerase; RdRp, RNA-dependent RNA polymerase; S, surface protein; SHBs, small surface protein; S-HDAg, small hepatitis delta antigen; VP, viral protein; X, X-domain/ADP-ribose-binding module. Important secondary structures are depicted below genomes.

      Envelopment might not be conserved among animal hepatitis viruses

      Recent studies revealed that HAV and HEV, thought previously to be non-enveloped viruses, exist in an enveloped form in blood, referred to as quasi-envelopment (Fig. 2).
      • Feng Z.
      • Hensley L.
      • McKnight K.L.
      • Hu F.
      • Madden V.
      • Ping L.
      • et al.
      A pathogenic picornavirus acquires an envelope by hijacking cellular membranes.
      • Takahashi M.
      • Tanaka T.
      • Takahashi H.
      • Hoshino Y.
      • Nagashima S.
      • Jirintai
      • et al.
      Hepatitis E Virus (HEV) strains in serum samples can replicate efficiently in cultured cells despite the coexistence of HEV antibodies: characterization of HEV virions in blood circulation.
      In contrast to enveloped viruses, there is no hint of virus-encoded proteins in the quasi-envelope of HAV and HEV, which raises questions on how quasi-enveloped viruses enter susceptible cells (summarised in
      • Feng Z.
      • Hirai-Yuki A.
      • McKnight K.L.
      • Lemon S.M.
      Naked viruses that aren’t always naked: quasi-enveloped agents of acute hepatitis.
      ). Interestingly, some non-primate HAV- and HEV-related viruses (henceforth, hepatoviruses and hepeviruses) lack critical genome structures involved in quasi-envelopment. This includes the apparent absence of a C-terminal VP1 capsid protein extension termed pX in some HAV-related bat viruses
      • Drexler J.F.
      • Corman V.M.
      • Lukashev A.N.
      • van den Brand J.M.
      • Gmyl A.P.
      • Brunink S.
      • et al.
      Evolutionary origins of hepatitis A virus in small mammals.
      and the lack of short amino acid motifs termed late domain motifs in several divergent hepeviruses from diverse mammals and birds.
      • Sander A.L.
      • Corman V.M.
      • Lukashev A.N.
      • Drexler J.F.
      Evolutionary Origins of Enteric Hepatitis Viruses.
      In contrast, HBV-related viruses (henceforth, hepadnaviruses) are enveloped viruses, yet fish were recently found to host a non-enveloped Hepadnaviridae sister family, termed Nackednaviridae.
      • Lauber C.
      • Seitz S.
      • Mattei S.
      • Suh A.
      • Beck J.
      • Herstein J.
      • et al.
      Deciphering the origin and evolution of hepatitis B viruses by means of a family of non-enveloped fish viruses.
      The discovery of nackednaviruses suggested that envelopment emerged de novo in hepadnaviruses capable of infecting mammals and ultimately humans.
      • Lauber C.
      • Seitz S.
      • Mattei S.
      • Suh A.
      • Beck J.
      • Herstein J.
      • et al.
      Deciphering the origin and evolution of hepatitis B viruses by means of a family of non-enveloped fish viruses.
      A hallmark of HCV infection is the formation of lipoviral particles, which incorporate both host-derived lipoproteins and virus-derived glycoproteins.
      • Catanese M.T.
      • Uryu K.
      • Kopp M.
      • Edwards T.J.
      • Andrus L.
      • Rice W.J.
      • et al.
      Ultrastructural analysis of hepatitis C virus particles.
      Interestingly, equine hepacivirus capsid proteins associate with intracellular lipid components, suggesting similarities between the replication of HCV and non-human HCV-related viruses (henceforth, hepaciviruses).
      • Tanaka T.
      • Kasai H.
      • Yamashita A.
      • Okuyama-Dobashi K.
      • Yasumoto J.
      • Maekawa S.
      • et al.
      Hallmarks of hepatitis C virus in equine hepacivirus.
      However, whether the formation of lipoviral particles is evolutionarily conserved among non-human hepaciviruses remains unknown.
      On the one hand, it is thus possible that envelopment and quasi-envelopment are not conserved among animal hepatitis viruses. On the other hand, ancestral animal hepatitis viruses may exploit unknown strategies for envelopment that differ from those found in human viruses.
      • Sander A.L.
      • Corman V.M.
      • Lukashev A.N.
      • Drexler J.F.
      Evolutionary Origins of Enteric Hepatitis Viruses.
      The de novo emergence of virus properties such as envelopment and recombination events may have contributed to the rise of viruses eventually pathogenic for humans

      Recombination events occurred during hepatitis virus evolution

      Recombination events among viruses can occur when 1 cell is co-infected with 2 different viruses that interact during replication. For all human hepatitis viruses, recombination has been exhaustively described.
      • Lemon S.M.
      • Murphy P.C.
      • Shields P.A.
      • Ping L.H.
      • Feinstone S.M.
      • Cromeans T.
      • et al.
      Antigenic and genetic variation in cytopathic hepatitis A virus variants arising during persistent infection: evidence for genetic recombination.
      • Chen X.
      • Zhang Q.
      • He C.
      • Zhang L.
      • Li J.
      • Zhang W.
      • et al.
      Recombination and natural selection in hepatitis E virus genotypes.
      • Locarnini S.
      • Littlejohn M.
      • Aziz M.N.
      • Yuen L.
      Possible origins and evolution of the hepatitis B virus (HBV).
      • Kalinina O.
      • Norder H.
      • Mukomolov S.
      • Magnius L.O.
      A natural intergenotypic recombinant of hepatitis C virus identified in St. Petersburg.
      • Lin C.C.
      • Lee C.C.
      • Lin S.H.
      • Huang P.J.
      • Li H.P.
      • Chang Y.S.
      • et al.
      RNA recombination in Hepatitis delta virus: identification of a novel naturally occurring recombinant.
      • Sy B.T.
      • Nguyen H.M.
      • Toan N.L.
      • Song L.H.
      • Tong H.V.
      • Wolboldt C.
      • et al.
      Identification of a natural intergenotypic recombinant hepatitis delta virus genotype 1 and 2 in Vietnamese HBsAg-positive patients.
      The plethora of recently discovered viruses has enabled revisiting the occurrence of recombination events during the genealogy of human hepatitis viruses and their animal homologues.
      For hepatoviruses there is evidence for recombination in the coding sequence of very distantly related viruses associated with different host orders, which hints at a broad host range.
      • Sander A.L.
      • Corman V.M.
      • Lukashev A.N.
      • Drexler J.F.
      Evolutionary Origins of Enteric Hepatitis Viruses.
      In addition, variations in the 5′-genome ends of animal hepatoviruses harbouring the internal ribosome entry site (IRES) hint at ancient recombination events involving different viral families.
      • Drexler J.F.
      • Corman V.M.
      • Lukashev A.N.
      • van den Brand J.M.
      • Gmyl A.P.
      • Brunink S.
      • et al.
      Evolutionary origins of hepatitis A virus in small mammals.
      For hepadnaviruses, the mosaic genome structure of extinct and extant HBV genotypes suggests that recombination has been a major micro-evolutionary feature of HBV evolution.
      • Locarnini S.
      • Littlejohn M.
      • Aziz M.N.
      • Yuen L.
      Possible origins and evolution of the hepatitis B virus (HBV).
      • Muhlemann B.
      • Jones T.C.
      • Damgaard P.B.
      • Allentoft M.E.
      • Shevnina I.
      • Logvin A.
      • et al.
      Ancient hepatitis B viruses from the Bronze Age to the Medieval period.
      Recombination among viruses associated with different host species was also described among primate and bird hepadnaviruses.
      • Yang J.
      • Xi Q.
      • Deng R.
      • Wang J.
      • Hou J.
      • Wang X.
      Identification of interspecies recombination among hepadnaviruses infecting cross-species hosts.
      Whether inter-host recombination events also occurred during the genealogy of the newly identified bat and cat hepadnaviruses demands further investigation. For non-human hepaciviruses, recombination events among diverse hosts have not been unambiguously proven yet.
      • Theze J.
      • Lowes S.
      • Parker J.
      • Pybus O.G.
      Evolutionary and phylogenetic analysis of the hepaciviruses and pegiviruses.
      However, as with hepatoviruses, hints for ancient recombination events are found in the 5′-genome ends of non-primate hepaciviruses, likely involving viruses belonging to different genera.
      • Drexler J.F.
      • Corman V.M.
      • Muller M.A.
      • Lukashev A.N.
      • Gmyl A.
      • Coutard B.
      • et al.
      Evidence for novel hepaciviruses in rodents.
      For hepeviruses, there is evidence for recombination involving different host orders, similar to hepatoviruses.
      • Sander A.L.
      • Corman V.M.
      • Lukashev A.N.
      • Drexler J.F.
      Evolutionary Origins of Enteric Hepatitis Viruses.
      Importantly, the camelid-associated HEV genotypes 7 and 8 show evidence of recombination at the boundary of ORFs encoding non-structural and structural proteins.
      • Sander A.L.
      • Corman V.M.
      • Lukashev A.N.
      • Drexler J.F.
      Evolutionary Origins of Enteric Hepatitis Viruses.
      Whether recombination events in these HEV strains contribute to their zoonotic potential is an intriguing question. Notably, recombination events likely enabled the rise of the family Hepeviridae per se, as the different hepevirus ORFs are derived from diverse alphavirus- and astrovirus-like ancestors.
      • Kelly A.G.
      • Netzler N.E.
      • White P.A.
      Ancient recombination events and the origins of hepatitis E virus.
      To summarise, recombination was likely a frequent event during the genealogy of hepatitis viruses. Whether transmission to humans is a consequence of recombination events in animal reservoirs requires further elucidation.

      Distinct features of HDV

      HDV is not a complete virus but a subviral agent with a very short, circular RNA genome which can replicate autonomously within a cell but requires the surface proteins of HBV for cell release and uptake (Fig. 2).
      • Hughes S.A.
      • Wedemeyer H.
      • Harrison P.M.
      Hepatitis delta virus.
      Of all human hepatitis viruses, the least is known about the origin of HDV. HDV has been hypothesised to have originated from plant viroids, via recombination with cellular mRNA, or from RNA intermediates of HBV.
      • Robertson H.D.
      How did replicating and coding RNAs first get together?.
      • Taylor J.M.
      Host RNA circles and the origin of hepatitis delta virus.
      • Cunha C.
      • Tavanez J.P.
      • Gudima S.
      Hepatitis delta virus: a fascinating and neglected pathogen.
      However, these theories are conflicting and not supported by experimental evidence. Interestingly, HDV-like agents were recently detected in a pool of oropharyngeal and cloacal samples of ducks and in various tissues of snakes.
      • Wille M.
      • Netter H.J.
      • Littlejohn M.
      • Yuen L.
      • Shi M.
      • Eden J.-S.
      • et al.
      A divergent hepatitis D-like agent in birds.
      • Hetzel U.
      • Szirovicza L.
      • Smura T.
      • Prahauser B.
      • Vapalahti O.
      • Kipar A.
      • et al.
      Identification of a novel deltavirus in Boa constrictor.
      The apparent lack of detectable hepadnaviruses in these preliminary investigations seems consistent with the lack of a predicted large delta antigen containing the C-terminal farnesylation signal required for interaction with the HBV envelope (Fig. 2).
      • Polson A.G.
      • Bass B.L.
      • Casey J.L.
      RNA editing of hepatitis delta virus antigenome by dsRNA-adenosine deaminase.
      • Otto J.C.
      • Casey P.J.
      The hepatitis delta virus large antigen is farnesylated both in vitro and in animal cells.
      On the one hand, this may indicate that the unique association of HDV with HBV is not evolutionarily conserved. On the other hand, divergent helper viruses and divergent mechanisms of envelopment cannot be excluded based on present knowledge. Although snake and duck HDV-like agents are genetically clearly distinct from human HDV, they show typical HDV genome properties, including the ORF encoding the small delta antigen, genomic and antigenomic ribozymes mediating autocatalytic cleavage and an extremely high degree of genomic self-complementarity of the circular genome. The detection of these divergent viruses in ancient vertebrates strongly suggests that other HDV-like viruses exist, which might include ancestors of human HDV.

      Chapter 3: Evolutionary conservation of infection patterns

      The comparison of hepatitis virus infection patterns among human and non-human hosts might reveal unique viral properties that eventually enabled human infection. For example, chronic courses of viral infections in animal reservoirs were found to be a strong predictor of human-to-human transmissibility after zoonotic introduction into humans.
      • Geoghegan J.L.
      • Senior A.M.
      • Di Giallonardo F.
      • Holmes E.C.
      Virological factors that increase the transmissibility of emerging human viruses.
      Here, we compare transmission routes, organ tropism, disease outcomes, receptor usage and immune evasion strategies among human and non-human hepatitis viruses.

      Conservation of transmission routes among hepatitis viruses

      Human hepatitis viruses differ in their transmission routes. HAV and HEV are mainly transmitted through the enteric route. Similarly, faecal shedding has been observed invariably in non-human hosts of hepatoviruses and hepeviruses (Table 2). In contrast, HBV and HDV are transmitted via blood and other body fluids, including semen and vaginal secretions.
      • Hughes S.A.
      • Wedemeyer H.
      • Harrison P.M.
      Hepatitis delta virus.
      • MacLachlan J.H.
      • Cowie B.C.
      Hepatitis B virus epidemiology.
      In addition, there is a high risk of perinatal transmission of HBV.
      • Gentile I.
      • Borgia G.
      Vertical transmission of hepatitis B virus: challenges and solutions.
      Like in humans, both perinatal and horizontal HBV transmission has been described for gibbons.
      • Noppornpanth S.
      • Haagmans B.L.
      • Bhattarakosol P.
      • Ratanakorn P.
      • Niesters H.G.
      • Osterhaus A.D.
      • et al.
      Molecular epidemiology of gibbon hepatitis B virus transmission.
      For non-primate hosts, vertical hepadnavirus transmission is known to be effective in rodents and birds.
      • Tagawa M.
      • Robinson W.S.
      • Marion P.L.
      Duck hepatitis B virus replicates in the yolk sac of developing embryos.
      • Kulonen K.
      • Millman I.
      Vertical transmission of woodchuck hepatitis virus.
      Based on a higher prevalence in female tent-making bats compared to males, predominantly sexual virus transmission has been suggested for the Tent-making bat HBV (TBHBV)
      • Hiller T.
      • Rasche A.
      • Brändel S.D.
      • König A.
      • Jeworowski L.
      • Teague O'Mara M.
      • et al.
      Host Biology and Anthropogenic Factors Affect Hepadnavirus Infection in a Neotropical Bat.
      . Transmission routes for other bat or cat hepadnaviruses remain unknown.
      • Drexler J.F.
      • Geipel A.
      • Konig A.
      • Corman V.M.
      • van Riel D.
      • Leijten L.M.
      • et al.
      • Aghazadeh M.
      • Shi M.
      • Barrs V.R.
      • McLuckie A.
      • Lindsay S.
      • Jameson B.
      • et al.
      A novel hepadnavirus identified in an immunocompromised domestic cat in Australia.
      HCV is a blood-borne virus. However, perinatal transmission rates are much lower for HCV than HBV and sexual transmission is rare.
      • Webster D.P.
      • Klenerman P.
      • Dusheiko G.M.
      Hepatitis C.
      • Terrault N.A.
      • Dodge J.L.
      • Murphy E.L.
      • Tavis J.E.
      • Kiss A.
      • Levin T.R.
      • et al.
      Sexual transmission of hepatitis C virus among monogamous heterosexual couples: the HCV partners study.
      HCV is mainly transmitted via blood transfusions, sharing of equipment in injecting drug use and reuse of injection needles in healthcare,
      • Webster D.P.
      • Klenerman P.
      • Dusheiko G.M.
      Hepatitis C.
      which raises questions on the transmission mode of HCV in scattered prehistoric human populations. Here, fights, use of weapons or tools as well as cultural or religious practices such as tattooing, circumcision, acupuncture or scarification might have enabled virus transmission.
      • Simmonds P.
      The origin of hepatitis C virus.
      Transmission routes among non-human hepaciviruses are unclear. In small mammals, transmission of hepaciviruses through biting and scratching associated with mating and territorial behaviour is conceivable.
      • Schmid J.
      • Rasche A.
      • Eibner G.
      • Jeworowski L.
      • Page R.A.
      • Corman V.M.
      • et al.
      Ecological drivers of Hepacivirus infection in a neotropical rodent inhabiting landscapes with various degrees of human environmental change.
      In horses, parenteral transmission of equine hepacivirus has been suggested,
      • Pfaender S.
      • Cavalleri J.M.
      • Walter S.
      • Doerrbecker J.
      • Campana B.
      • Brown R.J.
      • et al.
      Clinical course of infection and viral tissue tropism of hepatitis C virus-like nonprimate hepaciviruses in horses.
      • Ramsay J.D.
      • Evanoff R.
      • Wilkinson Jr., T.E.
      • Divers T.J.
      • Knowles D.P.
      • Mealey R.H.
      Experimental transmission of equine hepacivirus in horses as a model for hepatitis C virus.
      possibly including sexual transmission and veterinary practices.
      • Walter S.
      • Rasche A.
      • Moreira-Soto A.
      • Pfaender S.
      • Bletsa M.
      • Corman V.M.
      • et al.
      Infection patterns and recent evolutionary origins of equine hepaciviruses in donkeys.
      • Pfaender S.
      • Cavalleri J.M.
      • Walter S.
      • Doerrbecker J.
      • Campana B.
      • Brown R.J.
      • et al.
      Clinical course of infection and viral tissue tropism of hepatitis C virus-like nonprimate hepaciviruses in horses.
      Transmission via human-aided routes would suggest a relatively recent spread of this virus among equines worldwide and is consistent with the low virus diversity found in equines.
      • Burbelo P.D.
      • Dubovi E.J.
      • Simmonds P.
      • Medina J.L.
      • Henriquez J.A.
      • Mishra N.
      • et al.
      Serology-enabled discovery of genetically diverse hepaciviruses in a new host.
      • Walter S.
      • Rasche A.
      • Moreira-Soto A.
      • Pfaender S.
      • Bletsa M.
      • Corman V.M.
      • et al.
      Infection patterns and recent evolutionary origins of equine hepaciviruses in donkeys.
      • Pfaender S.
      • Cavalleri J.M.
      • Walter S.
      • Doerrbecker J.
      • Campana B.
      • Brown R.J.
      • et al.
      Clinical course of infection and viral tissue tropism of hepatitis C virus-like nonprimate hepaciviruses in horses.
      • Lyons S.
      • Kapoor A.
      • Sharp C.
      • Schneider B.S.
      • Wolfe N.D.
      • Culshaw G.
      • et al.
      Nonprimate hepaciviruses in domestic horses, United kingdom.
      Similar transmission routes are conceivable for cattle hepaciviruses.
      • Corman V.M.
      • Grundhoff A.
      • Baechlein C.
      • Fischer N.
      • Gmyl A.
      • Wollny R.
      • et al.
      Highly divergent hepaciviruses from African cattle.
      • Baechlein C.
      • Fischer N.
      • Grundhoff A.
      • Alawi M.
      • Indenbirken D.
      • Postel A.
      • et al.
      Identification of a novel hepacivirus in domestic cattle from Germany.
      Table 2Evolutionary conservation of infection patterns.
      Hallmarks of

      human infection
      Hallmarks of infection in non-human animals
      Naturally or experimentally infected with autochthonous virusExperimentally infected with human virus
      HAVLong faecal shedding;

      Quasi-envelopment;

      Never chronic but may cause protracted infections of up to one year;

      Faecal-oral transmission
      Bat, rodent, hedgehog, shrew: Acute infection; Faecal shedding; Hepatotropism
      • Drexler J.F.
      • Corman V.M.
      • Lukashev A.N.
      • van den Brand J.M.
      • Gmyl A.P.
      • Brunink S.
      • et al.
      Evolutionary origins of hepatitis A virus in small mammals.


      Woodchuck: Mild fever; Faecal shedding; Hepatotropism
      • Yu J.M.
      • Li L.L.
      • Xie G.C.
      • Zhang C.Y.
      • Ao Y.Y.
      • Duan Z.J.
      Experimental infection of Marmota monax with a novel hepatitis A virus.
      Chimpanzee: Faecal shedding; Quasi-envelopment; Acute hepatitis
      • Feng Z.
      • Hensley L.
      • McKnight K.L.
      • Hu F.
      • Madden V.
      • Ping L.
      • et al.
      A pathogenic picornavirus acquires an envelope by hijacking cellular membranes.
      • Emerson S.U.
      • Tsarev S.A.
      • Govindarajan S.
      • Shapiro M.
      • Purcell R.H.
      A simian strain of hepatitis A virus, AGM-27, functions as an attenuated vaccine for chimpanzees.
      • Dienstag J.L.
      • Feinstone S.M.
      • Purcell R.H.
      • Hoofnagle J.H.
      • Barker L.F.
      • London W.T.
      • et al.
      Experimental infection of chimpanzees with hepatitis A virus.


      New and Old World monkeys: Faecal shedding; Hepatotropism
      • LeDuc J.W.
      • Lemon S.M.
      • Keenan C.M.
      • Graham R.R.
      • Marchwicki R.H.
      • Binn L.N.
      Experimental infection of the New World owl monkey (Aotus trivirgatus) with hepatitis A virus.
      • Amado L.A.
      • Marchevsky R.S.
      • de Paula V.S.
      • Hooper C.
      • Freire Mda S.
      • Gaspar A.M.
      • et al.
      Experimental hepatitis A virus (HAV) infection in cynomolgus monkeys (Macaca fascicularis): evidence of active extrahepatic site of HAV replication.
      • Maynard J.E.
      • Lorenz D.
      • Bradley D.W.
      • Feinstone S.M.
      • Krushak D.H.
      • Barker L.F.
      • et al.
      Review of infectivity studies in nonhuman primates with virus-like particles associated with MS-1 hepatitis.


      Guinea pig: Faecal shedding; Hepatotropism; Subclinical disease
      • Hornei B.
      • Kammerer R.
      • Moubayed P.
      • Frings W.
      • Gauss-Muller V.
      • Dotzauer A.
      Experimental hepatitis A virus infection in guinea pigs.
      HBVOncogenic (HCC);

      Age-dependent chronicity rate;

      Vertical, parenteral, sexual transmission;

      Acute, fulminant courses in adults
      New World primates: Acute and chronic; Hepatitis; Vertical transmission
      • Lanford R.E.
      • Chavez D.
      • Brasky K.M.
      • Burns 3rd, R.B.
      • de Carvalho Dominguez Souza B.F.
      • Konig A.
      • Rasche A.
      • de Oliveira Carneiro I.
      • Stephan N.
      • Corman V.M.
      • et al.
      A novel hepatitis B virus species discovered in capuchin monkeys sheds new light on the evolution of primate hepadnaviruses.


      Old World primates:

      Acute and chronic; Horizontal and vertical transmission; Hepatitis
      • Noppornpanth S.
      • Haagmans B.L.
      • Bhattarakosol P.
      • Ratanakorn P.
      • Niesters H.G.
      • Osterhaus A.D.
      • et al.
      Molecular epidemiology of gibbon hepatitis B virus transmission.
      • Norder H.
      • Ebert J.W.
      • Fields H.A.
      • Mushahwar I.K.
      • Magnius L.O.
      Complete sequencing of a gibbon hepatitis B virus genome reveals a unique genotype distantly related to the chimpanzee hepatitis B virus.
      • Warren K.S.
      • Heeney J.L.
      • Swan R.A.
      • Heriyanto
      • Verschoor E.J.
      A new group of hepadnaviruses naturally infecting orangutans (Pongo pygmaeus).


      Bats: Apparently acute and chronic; Sexual transmission
      • Drexler J.F.
      • Geipel A.
      • Konig A.
      • Corman V.M.
      • van Riel D.
      • Leijten L.M.
      • et al.
      • Hiller T.
      • Rasche A.
      • Brändel S.D.
      • König A.
      • Jeworowski L.
      • Teague O'Mara M.
      • et al.
      Host Biology and Anthropogenic Factors Affect Hepadnavirus Infection in a Neotropical Bat.


      Woodchuck: Acute and chronic; Hepatitis; Oncogenic; Hepatotropism
      • Coffin C.S.
      • Michalak T.I.
      Persistence of infectious hepadnavirus in the offspring of woodchuck mothers recovered from viral hepatitis.
      (summarised in
      • Dandri M.
      • Petersen J.
      Animal models of HBV infection.
      )

      Squirrels: Hepatitis
      • Feitelson M.A.
      • Millman I.
      • Halbherr T.
      • Simmons H.
      • Blumberg B.S.
      A newly identified hepatitis B type virus in tree squirrels.
      ; Oncogenic
      • Testut P.
      • Renard C.A.
      • Terradillos O.
      • Vitvitski-Trepo L.
      • Tekaia F.
      • Degott C.
      • et al.
      A new hepadnavirus endemic in arctic ground squirrels in Alaska.


      Cat: Viremia
      • Aghazadeh M.
      • Shi M.
      • Barrs V.R.
      • McLuckie A.
      • Lindsay S.
      • Jameson B.
      • et al.
      A novel hepadnavirus identified in an immunocompromised domestic cat in Australia.


      Duck: Acute and chronic
      • Omata M.
      • Uchiumi K.
      • Ito Y.
      • Yokosuka O.
      • Mori J.
      • Terao K.
      • et al.
      Duck hepatitis B virus and liver diseases.
      ; Hepatitis; Vertical transmission; Not oncogenic; No exclusive hepatotropism (summarised in
      • Dandri M.
      • Petersen J.
      Animal models of HBV infection.
      • Rasche A.
      • Souza B.
      • Drexler J.F.
      Bat hepadnaviruses and the origins of primate hepatitis B viruses.
      )
      Chimpanzee: Acute and chronic; Hepatitis; Oncogenic (summarised in
      • Wieland S.F.
      The chimpanzee model for hepatitis B virus infection.
      • Lanford R.E.
      • Walker C.M.
      • Lemon S.M.
      The chimpanzee model of viral hepatitis: advances in understanding the immune response and treatment of viral hepatitis.
      )

      Tupaia: Acute and chronic; Hepatitis
      • Ruan P.
      • Yang C.
      • Su J.
      • Cao J.
      • Ou C.
      • Luo C.
      • et al.
      Histopathological changes in the liver of tree shrew (Tupaia belangeri chinensis) persistently infected with hepatitis B virus.
      ; Low viremia (summarised in
      • Dandri M.
      • Petersen J.
      Animal models of HBV infection.
      )
      HCVOncogenic (HCC);

      High chronicity rate;

      Parenteral transmission
      Cattle: Apparently acute and chronic; Hepatotropism
      • Corman V.M.
      • Grundhoff A.
      • Baechlein C.
      • Fischer N.
      • Gmyl A.
      • Wollny R.
      • et al.
      Highly divergent hepaciviruses from African cattle.
      • Baechlein C.
      • Fischer N.
      • Grundhoff A.
      • Alawi M.
      • Indenbirken D.
      • Postel A.
      • et al.
      Identification of a novel hepacivirus in domestic cattle from Germany.


      Horse: Apparently acute and chronic; Hepatotropism
      • Pfaender S.
      • Cavalleri J.M.
      • Walter S.
      • Doerrbecker J.
      • Campana B.
      • Brown R.J.
      • et al.
      Clinical course of infection and viral tissue tropism of hepatitis C virus-like nonprimate hepaciviruses in horses.


      Rat: Hepatotropism
      • Firth C.
      • Bhat M.
      • Firth M.A.
      • Williams S.H.
      • Frye M.J.
      • Simmonds P.
      • et al.
      Detection of zoonotic pathogens and characterization of novel viruses carried by commensal Rattus norvegicus in New York City.


      Bank vole: Hepatotropism
      • Drexler J.F.
      • Corman V.M.
      • Muller M.A.
      • Lukashev A.N.
      • Gmyl A.
      • Coutard B.
      • et al.
      Evidence for novel hepaciviruses in rodents.


      Marmoset: Acute and chronic; Hepatitis
      • Iwasaki Y.
      • Mori K.
      • Ishii K.
      • Maki N.
      • Iijima S.
      • Yoshida T.
      • et al.
      Long-term persistent GBV-B infection and development of a chronic and progressive hepatitis C-like disease in marmosets.


      Tamarin: Acute hepatitis; High viral titres
      • Bukh J.
      • Apgar C.L.
      • Yanagi M.
      Toward a surrogate model for hepatitis C virus: An infectious molecular clone of the GB virus-B hepatitis agent.
      Chimpanzee: Acute and chronic; Hepatitis; Oncogenic
      • Fernandez J.
      • Taylor D.
      • Morhardt D.R.
      • Mihalik K.
      • Puig M.
      • Rice C.M.
      • et al.
      Long-term persistence of infection in chimpanzees inoculated with an infectious hepatitis C virus clone is associated with a decrease in the viral amino acid substitution rate and low levels of heterogeneity.
      • Bukh J.
      • Apgar C.L.
      • Engle R.
      • Govindarajan S.
      • Hegerich P.A.
      • Tellier R.
      • et al.
      Experimental infection of chimpanzees with hepatitis C virus of genotype 5a: genetic analysis of the virus and generation of a standardized challenge pool.
      (summarised in
      • Lanford R.E.
      • Walker C.M.
      • Lemon S.M.
      The chimpanzee model of viral hepatitis: advances in understanding the immune response and treatment of viral hepatitis.
      )

      Tupaia: Mild hepatitis; Acute and chronic; Oncogenic
      • Amako Y.
      • Tsukiyama-Kohara K.
      • Katsume A.
      • Hirata Y.
      • Sekiguchi S.
      • Tobita Y.
      • et al.
      Pathogenesis of hepatitis C virus infection in Tupaia belangeri.
      HDVHBV-dependent infection;

      Co-infection with HBV: Mild to severe acute disease;

      Superinfection with HBV: Mostly chronic, worsens disease outcome compared to HBV mono-infection
      Snake:

      No hepatotropism; Apparently independent of HBV
      • Hetzel U.
      • Szirovicza L.
      • Smura T.
      • Prahauser B.
      • Vapalahti O.
      • Kipar A.
      • et al.
      Identification of a novel deltavirus in Boa constrictor.
      Chimpanzee: Hepatotropism;

      HBV co-infection and superinfection;

      Co-infection: Mild disease;

      Superinfection: Acute severe disease, >50% subclinical chronic HDV infection
      • Negro F.
      • Bergmann K.F.
      • Baroudy B.M.
      • Satterfield W.C.
      • Popper H.
      • Purcell R.H.
      • et al.
      Chronic hepatitis D virus (HDV) infection in hepatitis B virus carrier chimpanzees experimentally superinfected with HDV.
      • Ponzetto A.
      • Negro F.
      • Popper H.
      • Bonino F.
      • Engle R.
      • Rizzetto M.
      • et al.
      Serial passage of hepatitis delta virus in chronic hepatitis B virus carrier chimpanzees.
      (summarised in
      • Gerin J.L.
      Animal models of hepatitis delta virus infection and disease.
      );

      Woodchuck: Uses WHV envelope;

      Hepatotropism;

      Acute and chronic (summarised in
      • Gerin J.L.
      Animal models of hepatitis delta virus infection and disease.
      )
      HEVLow chronicity rate;

      Quasi-envelopment;

      Mainly faecal-oral transmission;

      Zoonotic
      Rabbit: Faecal shedding; Acute and chronic hepatitis; Viremia
      • Han J.
      • Lei Y.
      • Liu L.
      • Liu P.
      • Xia J.
      • Zhang Y.
      • et al.
      SPF rabbits infected with rabbit hepatitis E virus isolate experimentally showing the chronicity of hepatitis.


      Rat: Faecal shedding; Apparent hepatotropism; Mild hepatitis
      • Johne R.
      • Plenge-Bonig A.
      • Hess M.
      • Ulrich R.G.
      • Reetz J.
      • Schielke A.
      Detection of a novel hepatitis E-like virus in faeces of wild rats using a nested broad-spectrum RT-PCR.
      • Li T.C.
      • Yoshizaki S.
      • Ami Y.
      • Suzaki Y.
      • Yasuda S.P.
      • Yoshimatsu K.
      • et al.
      Susceptibility of laboratory rats against genotypes 1, 3, 4, and rat hepatitis E viruses.


      Ferret: Faecal shedding; Viremia; Acute and chronic hepatitis
      • Li T.C.
      • Yang T.
      • Yoshizaki S.
      • Ami Y.
      • Suzaki Y.
      • Ishii K.
      • et al.
      Ferret hepatitis E virus infection induces acute hepatitis and persistent infection in ferrets.


      Bat: Faecal shedding; Viremia
      • Drexler J.F.
      • Seelen A.
      • Corman V.M.
      • Fumie Tateno A.
      • Cottontail V.
      • Melim Zerbinati R.
      • et al.
      Bats worldwide carry hepatitis E virus-related viruses that form a putative novel genus within the family Hepeviridae.


      Swine: Faecal shedding; Viremia; Acute and chronic
      • Schlosser J.
      • Eiden M.
      • Vina-Rodriguez A.
      • Fast C.
      • Dremsek P.
      • Lange E.
      • et al.
      Natural and experimental hepatitis E virus genotype 3-infection in European wild boar is transmissible to domestic pigs.
      • Schlosser J.
      • Vina-Rodriguez A.
      • Fast C.
      • Groschup M.H.
      • Eiden M.
      Chronically infected wild boar can transmit genotype 3 hepatitis E virus to domestic pigs.


      Moose: Faecal shedding; Mild hepatitis
      • Lin J.
      • Karlsson M.
      • Olofson A.S.
      • Belak S.
      • Malmsten J.
      • Dalin A.M.
      • et al.
      High prevalence of hepatitis e virus in Swedish moose–a phylogenetic characterization and comparison of the virus from different regions.


      Chicken: Hepatitis-splenomegaly syndrome
      • Payne C.J.
      • Ellis T.M.
      • Plant S.L.
      • Gregory A.R.
      • Wilcox G.E.
      Sequence data suggests big liver and spleen disease virus (BLSV) is genetically related to hepatitis E virus.


      Camel: Faecal shedding; Viremia
      • Woo P.C.
      • Lau S.K.
      • Teng J.L.
      • Tsang A.K.
      • Joseph M.
      • Wong E.Y.
      • et al.
      New hepatitis E virus genotype in camels, the Middle East.
      • Rasche A.
      • Saqib M.
      • Liljander A.M.
      • Bornstein S.
      • Zohaib A.
      • Renneker S.
      • et al.
      Hepatitis E virus infection in dromedaries, North and East Africa, United Arab Emirates, and Pakistan, 1983–2015.
      Chimpanzee: Severe acute hepatitis
      • Arankalle V.A.
      • Ticehurst J.
      • Sreenivasan M.A.
      • Kapikian A.Z.
      • Popper H.
      • Pavri K.M.
      • et al.
      Aetiological association of a virus-like particle with enterically transmitted non-A, non-B hepatitis.


      Macaque: Faecal shedding; Viremia; Hepatitis
      • Tsarev S.A.
      • Emerson S.U.
      • Tsareva T.S.
      • Yarbough P.O.
      • Lewis M.
      • Govindarajan S.
      • et al.
      Variation in course of hepatitis E in experimentally infected cynomolgus monkeys.
      • Erker J.C.
      • Desai S.M.
      • Schlauder G.G.
      • Dawson G.J.
      • Mushahwar I.K.
      A hepatitis E virus variant from the United States: molecular characterization and transmission in cynomolgus macaques.


      Swine: Faecal shedding; Mild hepatitis
      • Halbur P.G.
      • Kasorndorkbua C.
      • Gilbert C.
      • Guenette D.
      • Potters M.B.
      • Purcell R.H.
      • et al.
      Comparative pathogenesis of infection of pigs with hepatitis E viruses recovered from a pig and a human.
      HAV, hepatitis A virus; HBV, hepatitis B virus; HCV, hepatitis C virus; HDV, hepatitits delta virus; HEV, hepatitis E virus; HCC, hepatocellular carcinoma; WHV, woodchuck hepatitis virus.
      In sum, virus transmission seems to be evolutionary conserved among enteric hepatitis viruses and their homologues, while transmission routes of non-human hepadnaviruses and hepaciviruses are poorly understood.

      Determinants of hepatotropism are poorly understood

      For HAV and HEV, little is known about the viral and host factors that promote liver tropism in humans. In bat hepatoviruses, but in none of the other non-primate hepatoviruses, almost equal amounts of virus were detectable in the liver and spleen.
      • Drexler J.F.
      • Corman V.M.
      • Lukashev A.N.
      • van den Brand J.M.
      • Gmyl A.P.
      • Brunink S.
      • et al.
      Evolutionary origins of hepatitis A virus in small mammals.
      However, whether this is due to sequestered macrophages containing hepatovirus genetic material, as observed during experimental infections of mice with HAV,
      • Hirai-Yuki A.
      • Hensley L.
      • McGivern D.R.
      • Gonzalez-Lopez O.
      • Das A.
      • Feng H.
      • et al.
      MAVS-dependent host species range and pathogenicity of human hepatitis A virus.
      or due to extrahepatic viral replication remains to be determined.
      For HBV and HDV, after low-specific binding to heparin-sulfate proteoglycans (summarised in
      • Glebe D.
      • Bremer C.M.
      The molecular virology of hepatitis B virus.
      ), hepatocyte entry is mediated via the sodium taurocholate co-transporting polypeptide (NTCP for the human receptor, Ntcp for the homologous receptor in animals).
      • Yan H.
      • Zhong G.
      • Xu G.
      • He W.
      • Jing Z.
      • Gao Z.
      • et al.
      Sodium taurocholate cotransporting polypeptide is a functional receptor for human hepatitis B and D virus.
      These liver-specific receptors likely govern the hepatotropism of HBV and HDV.
      • Yan H.
      • Zhong G.
      • Xu G.
      • He W.
      • Jing Z.
      • Gao Z.
      • et al.
      Sodium taurocholate cotransporting polypeptide is a functional receptor for human hepatitis B and D virus.
      Interestingly, the avian hepadnavirus DHBV does not show a strict hepatotropism (summarised in
      • Rasche A.
      • Souza B.
      • Drexler J.F.
      Bat hepadnaviruses and the origins of primate hepatitis B viruses.
      ). This is potentially explained by the usage of a receptor that differs from that used by HBV. Notably, even among mammalian hepadnaviruses, Ntcp usage might not be conserved, as illustrated by the apparent lack of hNTCP usage of some bat hepadnaviruses and WHV.
      • Drexler J.F.
      • Geipel A.
      • Konig A.
      • Corman V.M.
      • van Riel D.
      • Leijten L.M.
      • et al.
      • Konig A.
      • Doring B.
      • Mohr C.
      • Geipel A.
      • Geyer J.
      • Glebe D.
      Kinetics of the bile acid transporter and hepatitis B virus receptor Na+/taurocholate cotransporting polypeptide (NTCP) in hepatocytes.
      In the snake delta-like agent, the apparent lack of hepatotropism may be associated with the absence of a detectable hepadnavirus (Table 2).
      • Hetzel U.
      • Szirovicza L.
      • Smura T.
      • Prahauser B.
      • Vapalahti O.
      • Kipar A.
      • et al.
      Identification of a novel deltavirus in Boa constrictor.
      For HCV, an important, yet not exclusive factor determining hepatotropism in humans is its interaction with the liver-specific micro RNA-122 (miR-122).
      • Jopling C.L.
      • Yi M.
      • Lancaster A.M.
      • Lemon S.M.
      • Sarnow P.
      Modulation of hepatitis C virus RNA abundance by a liver-specific MicroRNA.
      All known non-human hepaciviruses contain at least one miR-122 binding site in their 5′-genome ends, which may contribute to their apparently conserved hepatotropism.
      • Yu Y.
      • Scheel T.K.H.
      • Luna J.M.
      • Chung H.
      • Nishiuchi E.
      • Scull M.A.
      • et al.
      miRNA independent hepacivirus variants suggest a strong evolutionary pressure to maintain miR-122 dependence.
      • Simmonds P.
      • Becher P.
      • Bukh J.
      • Gould E.A.
      • Meyers G.
      • Monath T.
      • et al.
      ICTV virus taxonomy profile: Flaviviridae.
      Liver tropism is thus a widely, yet not perfectly conserved attribute of the animal homologues of human hepatitis viruses. Because the factors determining hepatotropism of human hepatitis viruses are not entirely understood, systems allowing experimental infections with the newly discovered animal viruses will hopefully provide urgently needed insights into the determinants of viral hepatotropism.

      Chronic courses of infection occur in diverse hepatitis virus hosts

      Prehistoric human populations were small and scattered, raising the question of how hepatitis viruses survived in these populations. This is illustrated by the disappearance of HAV in isolated populations due to the livelong immunity HAV infections engender (summarised in
      • Drexler J.F.
      • Corman V.M.
      • Lukashev A.N.
      • van den Brand J.M.
      • Gmyl A.P.
      • Brunink S.
      • et al.
      Evolutionary origins of hepatitis A virus in small mammals.
      ). In contrast to prehistoric humans, other hepatovirus hosts such as small mammals were abundant and widespread, which presumably aided viral survival in these populations.
      • Drexler J.F.
      • Corman V.M.
      • Lukashev A.N.
      • van den Brand J.M.
      • Gmyl A.P.
      • Brunink S.
      • et al.
      Evolutionary origins of hepatitis A virus in small mammals.
      In contrast to HAV, both HBV and HCV establish chronic infections in humans, which presumably favoured virus maintenance in prehistoric human populations and among NHPs. Chronic hepatitis virus infections are commonly defined as infections that persist for more than 6 months for HBV and HCV, and 3 months for HEV.
      • Terrault N.A.
      • Lok A.S.F.
      • McMahon B.J.
      • Chang K.M.
      • Hwang J.P.
      • Jonas M.M.
      • et al.
      Update on prevention, diagnosis, and treatment of chronic hepatitis B: AASLD 2018 hepatitis B guidance.
      • Kamar N.
      • Izopet J.
      • Dalton H.R.
      Chronic hepatitis e virus infection and treatment.
      • Westbrook R.H.
      • Dusheiko G.
      Natural history of hepatitis C.
      The chronicity rate varies drastically among human hepatitis viruses. Chronic HEV infections are very rare (<1% of infections) and almost exclusively occur in immunocompromised patients.
      • Kamar N.
      • Izopet J.
      • Pavio N.
      • Aggarwal R.
      • Labrique A.
      • Wedemeyer H.
      • et al.
      Hepatitis E virus infection.
      In contrast, chronic HCV infections are very frequent at up to 80–85% (Table 1).
      • Webster D.P.
      • Klenerman P.
      • Dusheiko G.M.
      Hepatitis C.
      For HBV, the chronicity rate varies depending on the age at which the infection occurs, with rates of up to 90% for infected neonates, 30% for children aged 1–5 years and less than 5% for older children and adults (summarised in
      • Paganelli M.
      • Stephenne X.
      • Sokal E.M.
      Chronic hepatitis B in children and adolescents.
      ).
      Interestingly, chronic courses of infection are not unique for human HBV and HCV. Similar to human HBV infection, the chronicity rate of the rodent-associated WHV is age-dependent. While animals infected as newborns generally develop chronic infections, WHV usually causes acute self-limiting infections in animals infected at older ages (summarised in
      • Dandri M.
      • Petersen J.
      Animal models of HBV infection.
      ). Chronic courses of hepadnavirus infections also occur in ducks, squirrels, and NHPs (Table 2).
      • Drexler J.F.
      • Geipel A.
      • Konig A.
      • Corman V.M.
      • van Riel D.
      • Leijten L.M.
      • et al.
      • Noppornpanth S.
      • Haagmans B.L.
      • Bhattarakosol P.
      • Ratanakorn P.
      • Niesters H.G.
      • Osterhaus A.D.
      • et al.
      Molecular epidemiology of gibbon hepatitis B virus transmission.
      • Norder H.
      • Ebert J.W.
      • Fields H.A.
      • Mushahwar I.K.
      • Magnius L.O.
      Complete sequencing of a gibbon hepatitis B virus genome reveals a unique genotype distantly related to the chimpanzee hepatitis B virus.
      • Warren K.S.
      • Heeney J.L.
      • Swan R.A.
      • Heriyanto
      • Verschoor E.J.
      A new group of hepadnaviruses naturally infecting orangutans (Pongo pygmaeus).
      • Testut P.
      • Renard C.A.
      • Terradillos O.
      • Vitvitski-Trepo L.
      • Tekaia F.
      • Degott C.
      • et al.
      A new hepadnavirus endemic in arctic ground squirrels in Alaska.
      • Omata M.
      • Uchiumi K.
      • Ito Y.
      • Yokosuka O.
      • Mori J.
      • Terao K.
      • et al.
      Duck hepatitis B virus and liver diseases.
      • Hu X.
      • Margolis H.S.
      • Purcell R.H.
      • Ebert J.
      • Robertson B.H.
      Identification of hepatitis B virus indigenous to chimpanzees.
      Whether chronic hepadnavirus infections occur in bats is unclear.
      • Drexler J.F.
      • Geipel A.
      • Konig A.
      • Corman V.M.
      • van Riel D.
      • Leijten L.M.
      • et al.
      Among non-human hepaciviruses, studies reporting chronic infections are scarce. Chronic hepacivirus infections with prolonged viremia for more than 6 months were sporadically observed in experimentally infected horses and naturally infected cattle.
      • Corman V.M.
      • Grundhoff A.
      • Baechlein C.
      • Fischer N.
      • Gmyl A.
      • Wollny R.
      • et al.
      Highly divergent hepaciviruses from African cattle.
      • Pfaender S.
      • Cavalleri J.M.
      • Walter S.
      • Doerrbecker J.
      • Campana B.
      • Brown R.J.
      • et al.
      Clinical course of infection and viral tissue tropism of hepatitis C virus-like nonprimate hepaciviruses in horses.
      • Scheel T.K.
      • Kapoor A.
      • Nishiuchi E.
      • Brock K.V.
      • Yu Y.
      • Andrus L.
      • et al.
      Characterization of nonprimate hepacivirus and construction of a functional molecular clone.
      The chronicity rates in horses and cattle thus seem to be much lower than in human HCV infections.
      • Corman V.M.
      • Grundhoff A.
      • Baechlein C.
      • Fischer N.
      • Gmyl A.
      • Wollny R.
      • et al.
      Highly divergent hepaciviruses from African cattle.
      • Pfaender S.
      • Cavalleri J.M.
      • Walter S.
      • Doerrbecker J.
      • Campana B.
      • Brown R.J.
      • et al.
      Clinical course of infection and viral tissue tropism of hepatitis C virus-like nonprimate hepaciviruses in horses.
      • Ramsay J.D.
      • Evanoff R.
      • Wilkinson Jr., T.E.
      • Divers T.J.
      • Knowles D.P.
      • Mealey R.H.
      Experimental transmission of equine hepacivirus in horses as a model for hepatitis C virus.
      For other non-human hepaciviruses, whether chronic infections occur remains unknown. Similarly, chronic courses of hepevirus infections in non-human hosts are largely unknown. Nonetheless, an apparent chronic HEV infection in wild boars and prolonged viral shedding in experimentally infected immunocompromised domestic swine, rabbits, and ferrets suggest that chronicity is not limited to human HEV infections.
      • Han J.
      • Lei Y.
      • Liu L.
      • Liu P.
      • Xia J.
      • Zhang Y.
      • et al.
      SPF rabbits infected with rabbit hepatitis E virus isolate experimentally showing the chronicity of hepatitis.
      • Li T.C.
      • Yang T.
      • Yoshizaki S.
      • Ami Y.
      • Suzaki Y.
      • Ishii K.
      • et al.
      Ferret hepatitis E virus infection induces acute hepatitis and persistent infection in ferrets.
      • Schlosser J.
      • Vina-Rodriguez A.
      • Fast C.
      • Groschup M.H.
      • Eiden M.
      Chronically infected wild boar can transmit genotype 3 hepatitis E virus to domestic pigs.
      • Cao D.
      • Cao Q.M.
      • Subramaniam S.
      • Yugo D.M.
      • Heffron C.L.
      • Rogers A.J.
      • et al.
      Pig model mimicking chronic hepatitis E virus infection in immunocompromised patients to assess immune correlates during chronicity.
      To conclude, many questions regarding chronic infections in animal hepatitis viruses are still unanswered. Translational animal models to assess therapeutics for chronic hepatitis B and E, and investigating viral pathogenesis will require some correlate of chronic infection, which may be conceivable given the evolutionary conservation of chronicity among several animal hepadnaviruses and hepaciviruses.
      Chronicity may have aided hepatitis B and hepatitis C virus survival in scattered prehistoric human populations.

      Mechanisms leading to HCC differ among hepatitis viruses

      Chronic hepatitis virus infections can result in severe disease outcomes, including cirrhosis and HCC.
      • Akinyemiju T.
      • Abera S.
      • Ahmed M.
      • Alam N.
      • Alemayohu M.A.
      • et al.
      Global Burden of Disease Liver Cancer C
      The Burden of Primary Liver Cancer and Underlying Etiologies From 1990 to 2015 at the Global, Regional, and National Level: Results From the Global Burden of Disease Study 2015.
      In humans, chronic HBV infections result in HCC in 15–40% of cases
      • Lok A.S.
      Chronic hepatitis B.
      and chronic HCV infections in approximately 2.5% of cases.
      • Ghouri Y.A.
      • Mian I.
      • Rowe J.H.
      Review of hepatocellular carcinoma: epidemiology, etiology, and carcinogenesis.
      Interestingly, woodchucks infected with WHV and ground squirrels infected with the genetically related ground squirrel hepatitis virus are at a high risk of developing HCC when infected at birth (summarised in
      • Mason W.S.
      Animal models and the molecular biology of hepadnavirus infection.
      ) (Table 2). While oncogenesis in woodchucks is mainly caused by N-myc gene activation via targeted insertion of hepadnaviral DNA into host DNA, oncogenesis in ground squirrels is associated with an activation of c-myc genes.
      • Hansen L.J.
      • Tennant B.C.
      • Seeger C.
      • Ganem D.
      Differential activation of myc gene family members in hepatic carcinogenesis by closely related hepatitis B viruses.
      For human HBV, the mechanisms of oncogenesis remain poorly understood. HBV DNA fragments can integrate into the hepatocyte genome during viral replication.
      • Seeger C.
      • Mason W.S.
      Molecular biology of hepatitis B virus infection.
      However, in contrast to rodent hepadnaviruses, no specific integration site associated with oncogenesis has been identified. Accumulation of integration events into genes that may enhance oncogenesis, such as those encoding the telomerase reverse transcriptase (TERT), a histone H3 lysine 4 methyltransferase (MLL4), and cyclin E1 (CCNE1) have been described,
      • Sung W.K.
      • Zheng H.
      • Li S.
      • Chen R.
      • Liu X.
      • Li Y.
      • et al.
      Genome-wide survey of recurrent HBV integration in hepatocellular carcinoma.
      • Zhao L.H.
      • Liu X.
      • Yan H.X.
      • Li W.Y.
      • Zeng X.
      • Yang Y.
      • et al.
      Genomic and oncogenic preference of HBV integration in hepatocellular carcinoma.
      but their contribution to oncogenesis is unclear. Furthermore, integration sites in tumour cells seem to be enhanced in sites critical for chromosome stability, such as in proximity to telomeres.
      • Zhao L.H.
      • Liu X.
      • Yan H.X.
      • Li W.Y.
      • Zeng X.
      • Yang Y.
      • et al.
      Genomic and oncogenic preference of HBV integration in hepatocellular carcinoma.
      In addition, the viral HBx protein promotes oncogenesis through complex interactions with the host cell, such as altering the expression of host oncogenes and tumour suppressors, stimulating cell-cycle entry by activating cyclins and cyclin-dependent kinase pathways and blocking apoptosis (summarised in
      • Mesri E.A.
      • Feitelson M.A.
      • Munger K.
      Human viral oncogenesis: a cancer hallmarks analysis.
      ). In humans, HBx also interacts with the structural maintenance of chromosomes (Smc) complex Smc5/6 and stabilises the extrachromosomal cccDNA (covalently closed circular DNA) produced during HBV replication.
      • Decorsiere A.
      • Mueller H.
      • van Breugel P.C.
      • Abdul F.
      • Gerossier L.
      • Beran R.K.
      • et al.
      Hepatitis B virus X protein identifies the Smc5/6 complex as a host restriction factor.
      Interestingly, HBx presumably emerged de novo in mammals during hepadnavirus evolution.
      • Suh A.
      • Weber C.C.
      • Kehlmaier C.
      • Braun E.L.
      • Green R.E.
      • Fritz U.
      • et al.
      Early mesozoic coexistence of amniotes and hepadnaviridae.
      Although the role of the HBx protein in non-human hepadnavirus infections is unknown, conservation of the HBx gene in mammalian orthohepadnaviruses suggests that HBx-mediated oncogenesis may be conceivable in diverse mammals. In concordance, ducks infected with avian hepadnaviruses lacking an HBx do not develop HCC (summarised in
      • Dandri M.
      • Petersen J.
      Animal models of HBV infection.
      ).
      In contrast to HBV, integration of viral genetic material into the host genome does not occur during HCV infections. Here, the core protein and non-structural proteins NS3 and NS5A promote HCC development by altering the expression of host genes involved in diverse oncogenic pathways, including proteins involved in cell-cycle control (such as p53, p21, cyclins) and apoptosis (summarised in
      • Mesri E.A.
      • Feitelson M.A.
      • Munger K.
      Human viral oncogenesis: a cancer hallmarks analysis.
      ). Strikingly, HCC development has not been observed in any non-human hepacivirus host yet. Hypothetically, oncogenesis might either be unique to human HCV infections, or oncogenesis in animals has not been observed due to the relatively short life spans of the investigated animals, e.g. mice and rats infected with rat hepaciviruses.
      • Trivedi S.
      • Murthy S.
      • Sharma H.
      • Hartlage A.S.
      • Kumar A.
      • Gadi S.V.
      • et al.
      Viral persistence, liver disease, and host response in a hepatitis C-like virus rat model.
      In contrast to these rodents, some bat species have a comparably long life span of up to 30 years.
      • Wilkinson G.S.
      • South J.M.
      Life history, ecology and longevity in bats.
      However, whether bats can get chronically infected with hepaciviruses and if this infection leads to oncogenesis is unknown. In addition, it has been hypothesised that bats may have a lower risk of developing cancer than other mammals, potentially because of their unique physiological and immunological properties.
      • Wang L.F.
      • Walker P.J.
      • Poon L.L.
      Mass extinctions, biodiversity and mitochondrial function: are bats 'special' as reservoirs for emerging viruses?.
      In horses and cattle, chronic courses of hepacivirus infections have been described and it would be intriguing to study whether these large and relatively long-lived animals develop HCC. However, costly long-term infection studies and longitudinal epidemiological investigations will be needed to address this question.
      If and how animals infected with hepatitis viruses develop HCC is not well understood. HCC can be induced in mice, but this requires genetic engineering of the mouse genome, the use of chemotoxic agents, injection of tumour cells or xenograft approaches (summarised in
      • Brown Z.J.
      • Heinrich B.
      • Greten T.F.
      Mouse models of hepatocellular carcinoma: an overview and highlights for immunotherapy research.
      ). Both HBV and HCV can cause chronic infections and HCC in chimpanzees, but using chimpanzees as animal models is strongly restricted for ethical reasons. An essential step towards an animal model for oncogenic hepatitis is the identification of a tractable, long-living host with oncogenic mechanisms similar to human HBV and HCV infections.

      Receptor usage differs across hepatitis virus homologues

      A crucial step during viral infection and a major factor limiting cross-species transmission is the interaction of viral proteins with host cell membrane structures enabling viral attachment and entry into cells. Strikingly, the cellular receptor molecules of HAV and HEV are still unknown. Recent data revealed that contrary to textbook knowledge, TIM1 is not essential for HAV entry into hepatocytes or epithelial cells.
      • Das A.
      • Hirai-Yuki A.
      • Gonzalez-Lopez O.
      • Rhein B.
      • Moller-Tank S.
      • Brouillette R.
      • et al.
      TIM1 (HAVCR1) is not essential for cellular entry of either quasi-enveloped or naked hepatitis A virions.
      • Feigelstock D.
      • Thompson P.
      • Mattoo P.
      • Zhang Y.
      • Kaplan G.G.
      The human homolog of HAVcr-1 codes for a hepatitis A virus cellular receptor.
      HBV host specificity seems to be determined by a few essential amino acids of the cellular receptor NTCP/Ntcp. Interestingly, human HBV can use the Ntcp of great apes and New World monkeys, but 1 specific amino acid exchange in the Ntcp is needed for a cross-species transmission of human HBV to Old World monkeys.
      • de Carvalho Dominguez Souza B.F.
      • Konig A.
      • Rasche A.
      • de Oliveira Carneiro I.
      • Stephan N.
      • Corman V.M.
      • et al.
      A novel hepatitis B virus species discovered in capuchin monkeys sheds new light on the evolution of primate hepadnaviruses.
      • Muller S.F.
      • Konig A.
      • Doring B.
      • Glebe D.
      • Geyer J.
      Characterisation of the hepatitis B virus cross-species transmission pattern via Na+/taurocholate co-transporting polypeptides from 11 New World and Old World primate species.
      Similarly, 1 amino acid exchange in the woodchuck Ntcp enables an efficient infection with HBV.
      • Fu L.
      • Hu H.
      • Liu Y.
      • Jing Z.
      • Li W.
      Woodchuck sodium taurocholate cotransporting polypeptide supports low-level hepatitis B and D virus entry.
      However, additional unidentified host-specific co-factors might be essential for viral entry and infection. For example, while HDV infection of mouse hepatocytes can be enabled by alteration of just 3 amino acid residues in the murine Ntcp, HBV infection is not possible in these animals.
      • He W.
      • Cao Z.
      • Mao F.
      • Ren B.
      • Li Y.
      • Li D.
      • et al.
      Modification of three amino acids in sodium taurocholate cotransporting polypeptide renders mice susceptible to infection with hepatitis D virus in vivo.
      In addition, HBV infection can be enabled in pig and macaque hepatocytes expressing the human NTCP, but not in similarly engineered hepatocytes of mouse, rat, and dog origin.
      • Lempp F.A.
      • Wiedtke E.
      • Qu B.
      • Roques P.
      • Chemin I.
      • Vondran F.W.R.
      • et al.
      Sodium taurocholate cotransporting polypeptide is the limiting host factor of hepatitis B virus infection in macaque and pig hepatocytes.
      Strikingly, HBV can readily infect primary hepatocytes of the Asian tree shrew,
      • Kock J.
      • Nassal M.
      • MacNelly S.
      • Baumert T.F.
      • Blum H.E.
      • von Weizsacker F.
      Efficient infection of primary tupaia hepatocytes with purified human and woolly monkey hepatitis B virus.
      which implies that both the HBV cellular receptor and potential co-factors are conserved in this animal.
      For HCV, a complex interaction of various receptor molecules has been described
      • Catanese M.T.
      • Ansuini H.
      • Graziani R.
      • Huby T.
      • Moreau M.
      • Ball J.K.
      • et al.
      Role of scavenger receptor class B type I in hepatitis C virus entry: kinetics and molecular determinants.
      • Yamamoto S.
      • Fukuhara T.
      • Ono C.
      • Uemura K.
      • Kawachi Y.
      • Shiokawa M.
      • et al.
      Lipoprotein receptors redundantly participate in entry of hepatitis C virus.
      • Pileri P.
      • Uematsu Y.
      • Campagnoli S.
      • Galli G.
      • Falugi F.
      • Petracca R.
      • et al.
      Binding of hepatitis C virus to CD81.
      (Table 1). Like HBV, the host range of HCV seems to be limited by its receptors. Interestingly, rodents can be infected with HCV following modifications of either the host or the virus. On the host side, human liver-chimeric mice susceptible to HCV provide promising opportunities to circumvent host specificity.
      • Bissig K.D.
      • Wieland S.F.
      • Tran P.
      • Isogawa M.
      • Le T.T.
      • Chisari F.V.
      • et al.
      Human liver chimeric mice provide a model for hepatitis B and C virus infection and treatment.
      On the viral side, only 3 amino acid exchanges within the viral envelope proteins of HCV have been shown to allow infection of mouse hepatocytes in vitro, but additional adaptations might be necessary for efficient replication in vivo.
      • von Schaewen M.
      • Dorner M.
      • Hueging K.
      • Foquet L.
      • Gerges S.
      • Hrebikova G.
      • et al.
      Expanding the host range of hepatitis C virus through viral adaptation.
      Among non-human hepaciviruses, entry mechanisms have not been well studied, but the inability of the equine hepacivirus to infect human cells in vitro suggests a high level of host specificity.
      • Scheel T.K.
      • Kapoor A.
      • Nishiuchi E.
      • Brock K.V.
      • Yu Y.
      • Andrus L.
      • et al.
      Characterization of nonprimate hepacivirus and construction of a functional molecular clone.
      Recently detected hepaciviruses might provide exciting new opportunities for animal models, as exemplified by a rat hepacivirus capable of infecting immunocompetent laboratory mice and rats.
      • Trivedi S.
      • Murthy S.
      • Sharma H.
      • Hartlage A.S.
      • Kumar A.
      • Gadi S.V.
      • et al.
      Viral persistence, liver disease, and host response in a hepatitis C-like virus rat model.
      Notably, any tractable animal model of human hepatitis would greatly benefit from susceptibility to human viruses or recombinants thereof, which has rarely been achieved.

      Viral immune evasion strategies differ in host specificity

      In addition to viral entry, cross-species transmission is limited by host immune responses and the ability of viruses to evade these responses after host switching. Among other mechanisms, HAV and HCV evade the human innate immune response by cleavage of the mitochondrial antiviral signalling protein (MAVS). MAVS is an essential part of interferon pathways induced by viral double-stranded RNA.
      • Yang Y.
      • Liang Y.
      • Qu L.
      • Chen Z.
      • Yi M.
      • Li K.
      • et al.
      Disruption of innate immunity due to mitochondrial targeting of a picornaviral protease precursor.
      MAVS is cleaved by the HAV protease precursor 3ABC
      • Yang Y.
      • Liang Y.
      • Qu L.
      • Chen Z.
      • Yi M.
      • Li K.
      • et al.
      Disruption of innate immunity due to mitochondrial targeting of a picornaviral protease precursor.
      and the HCV protease NS3/4A
      • Horner S.M.
      • Gale Jr., M.
      Regulation of hepatic innate immunity by hepatitis C virus.
      at different sites. Strikingly different levels of host specificity are evident in HAV- and HCV-mediated MAVS cleavage. HAV-mediated MAVS cleavage seems to be rather host-specific based on the inability of human HAV to cleave murine MAVS.
      • Hirai-Yuki A.
      • Hensley L.
      • McGivern D.R.
      • Gonzalez-Lopez O.
      • Das A.
      • Feng H.
      • et al.
      MAVS-dependent host species range and pathogenicity of human hepatitis A virus.
      The ability of non-human hepatoviruses to cleave cognate and heterologous MAVS has not been studied yet and requires further investigation. Interestingly, for hepaciviruses, MAVS cleavage via the NS3/4A protease is conserved among equine, bat, rodent, and primate hepaciviruses,
      • Yang Y.
      • Liang Y.
      • Qu L.
      • Chen Z.
      • Yi M.
      • Li K.
      • et al.
      Disruption of innate immunity due to mitochondrial targeting of a picornaviral protease precursor.
      • Parera M.
      • Martrus G.
      • Franco S.
      • Clotet B.
      • Martinez M.A.
      Canine hepacivirus NS3 serine protease can cleave the human adaptor proteins MAVS and TRIF.
      • Anggakusuma Brown RJ
      • Banda D.H.
      • Todt D.
      • Vieyres G.
      • Steinmann E.
      • et al.
      Hepacivirus NS3/4A proteases interfere with MAVS signaling in both their cognate animal hosts and humans: implications for zoonotic transmission.
      hence reflecting a conserved immune evasion strategy. Strikingly, human MAVS can be cleaved by all of these diverse non-human hepaciviruses,
      • Anggakusuma Brown RJ
      • Banda D.H.
      • Todt D.
      • Vieyres G.
      • Steinmann E.
      • et al.
      Hepacivirus NS3/4A proteases interfere with MAVS signaling in both their cognate animal hosts and humans: implications for zoonotic transmission.
      hinting at a less host-specific mechanism compared to HAV.
      In conclusion, both virus-receptor interactions and host immune responses can restrict cross-species transmission. Understanding the underlying mechanisms is essential for adapting potential novel animal models to human hepatitis viruses.
      Some biological properties, such as hepatotropism, receptor usage or mechanisms leading to HCC differ among human hepatitis viruses and ancestral viruses carried by animals other than primates.
      Animal homologues of hepatitis B and C viruses provide novel opportunities for in vivo studies of viral pathogenesis.

      Chapter 4: Evolutionary origins of hepatitis viruses

      The plethora of newly discovered viruses provides insights into the genealogy of human hepatitis viruses.
      • Morse S.S.
      • Mazet J.A.
      • Woolhouse M.
      • Parrish C.R.
      • Carroll D.
      • Karesh W.B.
      • et al.
      Prediction and prevention of the next pandemic zoonosis.
      Here, we discuss hypotheses on the when, the whence, and the where of human hepatitis virus evolution.

      The age of human hepatitis viruses is underestimated

      For all human hepatitis viruses, projections of the most recent common ancestors (MRCA) based on extant viruses yield surprisingly similar results in the range of several thousand years before present.
      • Kulkarni M.A.
      • Walimbe A.M.
      • Cherian S.
      • Arankalle V.A.
      Full length genomes of genotype IIIA Hepatitis A virus strains (1995–2008) from India and estimates of the evolutionary rates and ages.
      • Forni D.
      • Cagliani R.
      • Pontremoli C.
      • Pozzoli U.
      • Vertemara J.
      • De Gioia L.
      • et al.
      Evolutionary analysis provides insight into the origin and adaptation of HCV.
      • Forni D.
      • Cagliani R.
      • Clerici M.
      • Sironi M.
      Origin and dispersal of Hepatitis E virus.
      Hypothetically, environmental factors such as the formation of large human populations, rearing of livestock and changes in land use might have contributed to the rise of hepatitis viruses in humans and explain the similarities of calculated MRCA. However, projections of ancient MRCA need to be treated with caution, because of the technical constraints of bioinformatic programmes, recombination events, and an inevitable sampling bias. These limitations are best illustrated by variations of the projected origins of HBV, which vary by several orders of magnitude.
      • Zhou Y.
      • Holmes E.C.
      Bayesian estimates of the evolutionary rate and age of hepatitis B virus.
      • Paraskevis D.
      • Angelis K.
      • Magiorkinis G.
      • Kostaki E.
      • Ho S.Y.
      • Hatzakis A.
      Dating the origin of hepatitis B virus reveals higher substitution rate and adaptation on the branch leading to F/H genotypes.
      • Zehender G.
      • Ebranati E.
      • Gabanelli E.
      • Sorrentino C.
      • Lo Presti A.
      • Tanzi E.
      • et al.
      Enigmatic origin of hepatitis B virus: an ancient travelling companion or a recent encounter?.
      In addition, ancient HBV sequences from mummies and human remains revealed that HBV strains closely related to contemporary strains already occurred in the Neolithic, strongly suggesting that HBV is much older than previously thought.
      • Kahila Bar-Gal G.
      • Kim M.J.
      • Klein A.
      • Shin D.H.
      • Oh C.S.
      • Kim J.W.
      • et al.
      Tracing hepatitis B virus to the 16th century in a Korean mummy.
      • Muhlemann B.
      • Jones T.C.
      • Damgaard P.B.
      • Allentoft M.E.
      • Shevnina I.
      • Logvin A.
      • et al.
      Ancient hepatitis B viruses from the Bronze Age to the Medieval period.
      • Krause-Kyora B.
      • Susat J.
      • Key F.M.
      • Kuhnert D.
      • Bosse E.
      • Immel A.
      • et al.
      Neolithic and medieval virus genomes reveal complex evolution of hepatitis B.
      The avian-associated hepadnaviruses were dated to have emerged around 6,000 years ago and thus again in a similar range as those yielded by projections of human-associated hepatitis virus MRCA.
      • Zhou Y.
      • Holmes E.C.
      Bayesian estimates of the evolutionary rate and age of hepatitis B virus.
      Again, the limitations of such projections became evident when endogenous hepadnavirus elements were identified in the genomes of birds and reptiles.
      • Suh A.
      • Weber C.C.
      • Kehlmaier C.
      • Braun E.L.
      • Green R.E.
      • Fritz U.
      • et al.
      Early mesozoic coexistence of amniotes and hepadnaviridae.
      • Suh A.
      • Brosius J.
      • Schmitz J.
      • Kriegs J.O.
      The genome of a Mesozoic paleovirus reveals the evolution of hepatitis B viruses.
      • Cui J.
      • Holmes E.C.
      Endogenous hepadnaviruses in the genome of the budgerigar (Melopsittacus undulatus) and the evolution of avian hepadnaviruses.
      • Liu W.
      • Pan S.
      • Yang H.
      • Bai W.
      • Shen Z.
      • Liu J.
      • et al.
      The first full-length endogenous hepadnaviruses: identification and analysis.
      • Gilbert C.
      • Meik J.M.
      • Dashevsky D.
      • Card D.C.
      • Castoe T.A.
      • Schaack S.
      Endogenous hepadnaviruses, bornaviruses and circoviruses in snakes.
      According to these molecular fossils, hepadnaviruses must have occurred in the Early Mesozoic > 200 million years ago (mya), predating the rise of mammals (Fig. 3A) and again exceeding the MRCA from bioinformatic calculations by several orders of magnitude.
      • Foley N.M.
      • Springer M.S.
      • Teeling E.C.
      Mammal madness: is the mammal tree of life not yet resolved?.
      Hepatitis viruses are much older than previously thought, with hepatitis B virus ancestors predating the rise of mammals.