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Natural history of chronic hepatitis B in Euro-Mediterranean and African Countries

  • Stephanos J. Hadziyannis
    Correspondence
    Address: Department of Medicine and Hepatology, Henry Dunant Hospital, 107 Messogion Ave., 115 26 Athens, Greece. Tel.: +30 210 6972937; fax: +30 210 6972974.
    Affiliations
    Department of Medicine and Hepatology, Henry Dunant Hospital, Athens, Greece
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Open AccessPublished:January 14, 2011DOI:https://doi.org/10.1016/j.jhep.2010.12.030
      Data derived from population, case-control, and cohort studies conducted in several Euro-Mediterranean and African countries disclose impressive similarities in the age and modes of hepatitis B virus (HBV) transmission and in the prevalence, duration, and outcome of the four phases of the natural history of chronic infection. Perinatal HBV infection is rare while the vast majority of chronic infections originate from horizontal HBV transmission to infants and children. HBeAg loss and seroconversion to anti-HBe occur in a few years time, usually during the second decade of life. HBeAg-negative/anti-HBe-positive chronic hepatitis B (CHB), predominates in these countries being 7–9 times more frequent than HBeAg-positive CHB. The predominance of HBeAg-negative CHB is largely linked to the molecular characteristics of HBV genotype D prevailing in European and African countries of the Mediterranean basin and of genotype E and subgenotype A1 that prevail in the other parts of Africa. The molecular characteristics of the African subgenotype A1 differ from those of European subgenotype A2 explaining the fact that patients infected subgenotype A1 demonstrate an earlier loss of HBeAg and seroconversion to anti-HBe during the natural course of HBV infection compared to those infected with subgenotype A2. It is proposed that the molecular characteristics of HBV genotypes and subgenotypes prevailing in Euro-Mediterranean and African countries acting in concert with host and environmental factors largely determine the natural history of chronic HBV infection and its significant differences from countries of HBV genotype C and B and of subgenotype Ae predominance. The knowledge of the natural history of chronic HBV infection in Euro-Mediterranean and African countries combined with wide screening programs for prompt recognition and treatment of chronic HBV infection both in its HBeAg-positive and -negative immune reactive phases can be expected to increase the efficacy of current and future therapeutic strategies.

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      Introduction

      Knowledge of the natural history of chronic hepatitis B virus (HBV) infection is essential in order to understand why HBV patients may present with greatly differing clinical, serological, biochemical, and liver histological profiles as well as why these characteristics may remain stable or change significantly over time. Good knowledge of the natural history of the infection and of the underlying HBV-induced liver disease is also crucial for the decision to treat or not, of how to treat and how to monitor both treated and untreated patients.
      However, the natural history of chronic HBV infection appears to exhibit significant geographical and other differences that may be linked to respective differences in viral, host, and environmental factors. The characteristics of chronic HBV infection in the Mediterranean Basin have hitherto been well described in many individual countries of this area; however, despite the existence of numerous common features that differ significantly from those in other geographical areas, a holistic view of its overall natural history in Euro-Mediterranean and African countries has not yet been attempted. Even in numerous, excellent reviews of the overall natural history of HBV infection and of its phases, little emphasis is given on the particular features prevailing in the Mediterranean area.
      It is the purpose of this article to critically review data on the natural history of chronic HBV infection in Euro-Mediterranean and African countries as compared to respective information derived from other geographical areas and to evaluate the possible role of viral, host, and other factors.
      In this review I thought it was necessary to start with a brief historical account on how the natural history concept has evolved over the years, followed by a concise review of current knowledge on when and how chronic HBV infection develops and by a description of the phases in its natural history.

      Historical view of the natural history of chronic HBV infection

      Up to the mid 1960’s nothing was really known on viral hepatitis B and on its natural history. Then in 1967 the scenery of hepatitis B opened by the demonstration that a serum protein, the Australia (Au) antigen, discovered in the early 1960s by Blumberg et al. [
      • Blumberg B.S.
      • Alter H.J.
      • Visnich S.
      A “new” antigen in leukemia sera.
      ], was specifically associated with viral hepatitis type B [
      • Giles J.P.
      • McCollum R.W.
      • Berndtson Jr., L.W.
      • Krugman S.
      Relation of Australia-SH antigen to the willowbrook MS-2 strain.
      ] and represented the coat protein of HBV itself [
      • Bayer M.E.
      • Blumberg B.S.
      • Werner B.
      Particles associated with Australia antigen in the sera of patients with leukaemia, Down’s Syndrome and hepatitis.
      ]. Worldwide seroepidemiological studies of Au antigen and its antibody, properly renamed to hepatitis B surface antigen (HBsAg) and antibody (anti-HBs), disclosed in the 1970s that HBV infection is a major global public health problem with nevertheless significant geographical variations [
      • Lavanchy D.
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      ,
      • Szmuness W.
      • Prince A.M.
      Epidemiologic patterns of viral hepatitis in eastern Europe in the light of recent findings concerning the serum hepatitis antigen.
      ]. It was also realized that individuals persistently positive for HBsAg differed in their characteristics and were, therefore, divided into two categories of chronic HBV infection: (a) those with chronic liver disease referred as chronic hepatitis B (CHB) patients and (b) those with chronic infection, but without any clinical and biochemical evidence of underlying liver damage, referred as “healthy” HBsAg carriers [
      • Szmuness W.
      • Prince A.M.
      Epidemiologic patterns of viral hepatitis in eastern Europe in the light of recent findings concerning the serum hepatitis antigen.
      ,
      • Hadziyannis S.
      • Merikas G.
      • Panetsos S.
      • Kourepi M.
      Hepatitis associated antigen carriers among blood donors in Greece.
      ]. Studies of the surface and core proteins of HBV in the liver by immunohistochemical techniques (Fig. 1) offered evidence in support of this early view that chronic HBV infection consists of two different types or subsets of patients, those with and those without liver disease [
      • Bianchi L.
      • Gudat F.
      Immunopathology of hepatitis B.
      ,
      • Hadziyannis S.
      • Gerber M.A.
      • Vissoulis C.
      • Popper H.
      Cytoplasmic hepatitis B antigen in “ground-glass” hepatocytes of carriers.
      ,
      • Ray M.B.
      • Desmet V.J.
      • Bradburne A.F.
      • Desmyter J.
      • Fevery J.
      • De Groote J.
      Differential distribution of hepatitis B surface antigen and hepatitis B core antigen in the liver of hepatitis B patients.
      ]. Then, another HBV protein, the hepatitis B e antigen (HBeAg) was discovered by Magnius and Espmark [
      • Magnius L.O.
      • Espmark A.
      A new antigen complex co-occurring with Australia antigen.
      ] and was added to the scenery of hepatitis B as a marker of HBV replication.
      Figure thumbnail gr1
      Fig. 1Microphotographs of liver histology and of HBsAg and HBcAg expression in the liver of an individual in the inactive HBsAg carrier state (A and B) and of a patient with chronic active HBV liver disease (C and D). There are numerous ground-glass hepatocytes in the otherwise normal liver of the inactive HBsAg carrier (A), loaded with HBsAg as shown by green immunofluorescent staining (B). Hepatitis B core antigen (HBcAg) expression was completely negative. Completely different is the picture of liver histology and immunohistochemistry of the patient with active chronic hepatitis B showing severe necroinflammation, fibrosis, and positive immunoperoxidase staining of HBcAg in the nuclei and cytoplasm of hepatocytes (C). HBsAg is also positive in several hepatocytes (D).
      Testing for serum HBeAg and its antibody (anti-HBe) by a sensitive radioimmunoassay (RIA) developed in 1978, in combination with liver biochemistries and histology, showed that HBsAg-positive patients with chronic hepatitis B were HBeAg-positive while “healthy” HBsAg carriers were HBeAg-negative/anti-HBe positive [
      • Hoofnagle J.H.
      • Dusheiko G.M.
      • Seeff L.B.
      • Jones E.A.
      • Waggoner J.G.
      • Bales Z.B.
      Seroconversion from hepatitis B e antigen to antibody in chronic type B hepatitis.
      ]. Chronic HBV infection in the above two groups was, therefore, labeled as “replicative” and “non-replicative”, respectively, and on the basis of follow-up data from a cohort of HBeAg-positive patients, it was proposed that they represented sequential phases in the natural course of chronic HBV infection rather than independent types of chronic hepatitis B [
      • Hoofnagle J.H.
      • Dusheiko G.M.
      • Seeff L.B.
      • Jones E.A.
      • Waggoner J.G.
      • Bales Z.B.
      Seroconversion from hepatitis B e antigen to antibody in chronic type B hepatitis.
      ,
      • Hoofnagle J.H.
      • Alter H.J.
      Chronic viral hepatitis.
      ]. It was also assumed and largely accepted that after HBeAg loss and seroconversion to anti-HBe, HBV becomes practically inactive. The fact that HBsAg continues to remain detectable was attributed to its expression and secretion in serum from HBsAg sequences integrated into the host genome [
      • Hadziyannis S.
      • Raimondo G.
      • Papaioannou C.
      • Anastassakos C.
      • Wong D.
      • Sninsky J.
      • et al.
      Expression of pre-S gene-encoded proteins in liver and serum during chronic hepatitis B virus infection in comparison to other markers of active virus replication.
      ,
      • Shafritz D.A.
      • Shouval D.
      • Sherman H.I.
      • Hadziyannis S.J.
      • Kew M.C.
      Integration of hepatitis B virus DNA into the genome of liver cells in chronic liver disease and hepatocellular carcinoma. Studies in percutaneous liver biopsies and post-mortem tissue specimens.
      ,
      • Yim H.J.
      • Lok A.S.
      Natural history of chronic hepatitis B virus infection: what we knew in 1981 and what we know in 2005.
      ]. Consistent with this concept was the information obtained by the application of non-sensitive dot-blot assays measuring serum HBV DNA with a limit of detection of approximately 1 million copies/ml.
      However, during the same period of the 1980s, studies in Asian patients revealed (mostly in children and young age groups) the existence of an early phase in the natural course of chronic HBV infection [
      • Chu C.M.
      • Karayiannis P.
      • Fowler M.J.
      • Monjardino J.
      • Liaw Y.F.
      • Thomas H.C.
      Natural history of chronic hepatitis B virus infection in Taiwan: studies of hepatitis B virus DNA in serum.
      ] during which HBeAg is positive, HBV DNA levels are very high but aminotransferases and liver histology remain nearly normal. This was considered to be an immune tolerant state and a 3-rather than a 2-phase natural history of chronic HBV infection was proposed. Concomitantly, the existence of HBeAg negative CHB was recognized in the Mediterranean area first on the basis of immunofluorescence studies [
      • Hadziyannis S.J.
      Anti-HBe positive chronic active hepatitis.
      ] and then by assays of serum HBV DNA [
      • Bonino F.
      • Rosina F.
      • Rizzetto M.
      • Rizzi R.
      • Chiaberge E.
      • Tardanico R.
      • et al.
      Chronic hepatitis in HBsAg carriers with serum HBV-DNA and anti-HBe.
      ,
      • Hadziyannis S.J.
      • Lieberman H.M.
      • Karvountzis G.G.
      • Shafritz D.A.
      Analysis of liver disease, nuclear HBcAg, viral replication, and hepatitis B virus DNA in liver and serum of HBeAg vs. Anti-HBe positive carriers of hepatitis B virus.
      ,
      • Lok A.S.
      • Hadziyannis S.J.
      • Weller I.V.
      • Karvountzis M.G.
      • Monjardino J.
      • Karayiannis P.
      • et al.
      Contribution of low level HBV replication to continuing inflammatory activity in patients with anti-HBe positive chronic hepatitis B virus infection.
      ] and was added to the natural history of chronic HBV infection as a late phase of HBV reactivation (Fig. 2). The application of sensitive assays for the measurement of serum HBV DNA by polymerase chain reaction (PCR) methods confirmed the earlier Mediterranean findings and the terms “replicative” and “non-replicative” phases were modified to “high” and “low” replicative, respectively [
      • Yim H.J.
      • Lok A.S.
      Natural history of chronic hepatitis B virus infection: what we knew in 1981 and what we know in 2005.
      ].
      Figure thumbnail gr2
      Fig. 2The proposed natural history of chronic HBV infection (modified from Ref.
      [
      • Hadziyannis S.J.
      Hepatitis B e antigen negative chronic hepatitis B: from clinical recognition to pathogenesis and treatment.
      ]
      ). The takeover of precore HBV mutant strains in the natural history of primary HBV infection with wild type, HBeAg-positive virus, as proposed by Brunetto et al.
      [
      • Brunetto M.R.
      • Giarin M.
      • Saracco G.
      • Oliveri F.
      • Calvo P.
      • Capra G.
      • et al.
      Hepatitis B virus unable to secrete e antigen and response to interferon in chronic hepatitis B.
      ]
      , is depicted in the lower part of the figure.
      Recently, a new scheme of the natural history of chronic HBV infection has been proposed based not only on the HBeAg/anti-HBe status but also on host immune activity against the replicating virus [
      • Hoofnagle J.H.
      • Doo E.
      • Liang T.J.
      • Fleischer R.
      • Lok A.S.
      Management of hepatitis B: summary of a clinical research workshop.
      ,
      • Lok A.S.
      • Heathcote E.J.
      • Hoofnagle J.H.
      Management of hepatitis B: 2000–summary of a workshop.
      ,

      Lok ASF, McMahon BJ. AASLD Practice Guidelines. Chronic hepatitis B: Update 2009. Accessed at www.aasld.org on October 2, 2010.

      ,
      • McMahon B.J.
      The natural history of chronic hepatitis B virus infection.
      ]

      When and how chronic HBV infection develops

      It is well established now that acute HBV infection may become chronic at highly variable rates depending on the age and modes of HBV transmission. The highest rates of transition of an acute infection to chronic (>80%) have been reported in cases of materno-fetal and neonatal HBV transmission from HBeAg-positive mothers [
      • Liaw Y.F.
      • Chu C.M.
      Hepatitis B virus infection.
      ,
      • Liaw Y.F.
      • Brunetto M.R.
      • Hadziyannis S.J.
      The natural history of chronic HBV infection and geographical differences.
      ]. Primary HBV infection in infancy and childhood has been found to become chronic at a much lower rate (20–30%). After childhood, the rates of transition to chronicity in otherwise healthy adults have been well documented and shown to be extremely low, even lower than 1% [
      • Chu C.M.
      • Hung S.J.
      • Lin J.
      • Tai D.I.
      • Liaw Y.F.
      Natural history of hepatitis B e antigen to antibody seroconversion in patients with normal serum aminotransferase levels.
      ], with the exception of immunocompromised individuals. The high rates of chronicity of HBV infection in neonates and toddlers have been largely attributed to the immaturity of the host immune system of these very young age groups. Moreover, data from sequencing of the infecting HBV strains have revealed that the sine qua non prerequisite of an acute HBV infection in order to become chronic, is that the infecting HBV strain may be of wild type (wt) in its precore region [
      • Cote P.J.
      • Korba B.E.
      • Miller R.H.
      • Jacob J.R.
      • Baldwin B.H.
      • Hornbuckle W.E.
      • et al.
      Effects of age and viral determinants on chronicity as an outcome of experimental woodchuck hepatitis virus infection.
      ,
      • Hadziyannis S.J.
      • Vassilopoulos D.
      Immunopathogenesis of hepatitis B e antigen negative chronic hepatitis B infection.
      ] and, therefore, producing HBeAg. Otherwise, acute infection will run a self-limited course regardless of the age at its acquisition. It is noteworthy that this knowledge has been acquired following the discovery of precore HBV mutants in the Mediterranean area [
      • Brunetto M.R.
      • Giarin M.
      • Saracco G.
      • Oliveri F.
      • Calvo P.
      • Capra G.
      • et al.
      Hepatitis B virus unable to secrete e antigen and response to interferon in chronic hepatitis B.
      ,
      • Carman W.F.
      • Jacyna M.R.
      • Hadziyannis S.
      • Karayiannis P.
      • McGarvey M.J.
      • Makris A.
      • et al.
      Mutation preventing formation of hepatitis B e antigen in patients with chronic hepatitis B infection.
      ]. However, since mixtures of wt and precore mutant HBV strains may also co-circulate in the same HBeAg-negative individual, it is possible that acute HBV infection acquired from an HBeAg negative person harboring such mixtures of HBV strains may turn out occasionally to become HBeAg-positive, provided that a precore wt HBV strain from the mixture becomes selected in the newly infected newborn [
      • Cote P.J.
      • Korba B.E.
      • Miller R.H.
      • Jacob J.R.
      • Baldwin B.H.
      • Hornbuckle W.E.
      • et al.
      Effects of age and viral determinants on chronicity as an outcome of experimental woodchuck hepatitis virus infection.
      ,
      • Candotti D.
      • Opare-Sem O.
      • Rezvan H.
      • Sarkodie F.
      • Allain J.P.
      Molecular and serological characterization of hepatitis B virus in deferred Ghanaian blood donors with and without elevated alanine aminotransferase.
      ]. However, expression of the HBe protein as a prerequisite for an acute hepatitis B to become chronic requires the immune tolerance of the host against HBV. This explains the very high rates of chronicity (90%) of HBV infection in neonates born to HBeAg + mothers [
      • Beasley R.P.
      • Trepo C.
      • Stevens C.E.
      • Szmuness W.
      The e antigen and vertical transmission of hepatitis B surface antigen.
      ], the intermediate rates in children and the extreme rarity (0.1%) of chronicity in a large numbers of immunocompetent Greek adults with a well documented diagnosis of primary, acute hepatitis B after exclusion of patients with acute exacerbations of chronic HBV infection [
      • Cote P.J.
      • Korba B.E.
      • Miller R.H.
      • Jacob J.R.
      • Baldwin B.H.
      • Hornbuckle W.E.
      • et al.
      Effects of age and viral determinants on chronicity as an outcome of experimental woodchuck hepatitis virus infection.
      ,
      • Tassopoulos N.C.
      • Papaevangelou G.J.
      • Sjogren M.H.
      • Roumeliotou-Karayannis A.
      • Gerin J.L.
      • Purcell R.H.
      Natural history of acute hepatitis B surface antigen-positive hepatitis in Greek adults.
      ].

      Phases in the natural history of chronic HBV infection

      On the basis of information derived from selected research and review articles [
      • Bell S.J.
      • Lau A.
      • Thompson A.
      • Watson K.J.
      • Demediuk B.
      • Shaw G.
      • et al.
      Chronic hepatitis B: recommendations for therapy based on the natural history of disease in Australian patients.
      ,
      • Chang M.H.
      Natural history of hepatitis B virus infection in children.
      ,
      • Fattovich G.
      Natural history and prognosis of hepatitis B.
      ,
      • Fattovich G.
      • Bortolotti F.
      • Donato F.
      Natural history of chronic hepatitis B: special emphasis on disease progression and prognostic factors.
      ,
      • Hadziyannis S.J.
      • Papatheodoridis G.V.
      Hepatitis B e antigen-negative chronic hepatitis B: natural history and treatment.
      ,
      • Hui C.K.
      • Leung N.
      • Yuen S.T.
      • Zhang H.Y.
      • Leung K.W.
      • Lu L.
      • et al.
      Natural history and disease progression in Chinese chronic hepatitis B patients in immune-tolerant phase.
      ,
      • Lai C.L.
      • Yuen M.F.
      The natural history of chronic hepatitis B.
      ,
      • Liaw Y.F.
      Natural history of chronic hepatitis B virus infection and long-term outcome under treatment.
      ,
      • Manno M.
      • Camma C.
      • Schepis F.
      • Bassi F.
      • Gelmini R.
      • Giannini F.
      • et al.
      Natural history of chronic HBV carriers in northern Italy: morbidity and mortality after 30 years.
      ,
      • McMahon B.J.
      Epidemiology and natural history of hepatitis B.
      ,
      • McMahon B.J.
      Natural history of chronic hepatitis B.
      ,
      • Ni Y.H.
      Natural history of hepatitis B virus infection: pediatric perspective.
      ,
      • Villeneuve J.P.
      The natural history of chronic hepatitis B virus infection.
      ,
      • Yuen M.F.
      Revisiting the natural history of chronic hepatitis B: impact of new concepts on clinical management.
      ] current views on the natural course of HBV infection and its phases can be summarized as following:
      Once HBV infection has become chronic, its subsequent course largely consists of four phases of variable duration and outcome of the underlying liver disease (Fig. 2). All phases have been linked pathogenetically to the level of HBV replication and the strength of the host immune reactivity against the replicating HBV. The first two phases are associated with HBeAg seropositivity while the other two develop after clearance of HBeAg and development of anti-HBe immunity [
      • Milich D.R.
      Molecular and genetic aspects of the immune responses to hepatitis B viral antigens.
      ,
      • Milich D.R.
      Immune response to hepatitis B virus proteins: relevance of the murine model.
      ]. Loss of HBsAg signals a most favorable outcome of chronic HBV infection and is generally regarded as the closest one to cure of the infection. This may occur spontaneously or can be induced by treatment in any phase of the natural history of chronic infection at different, however, rates. Moreover, transition from one to the next phase of chronicity is not recognizable in all patients either because it may not be an obligatory step in the overall natural course of the infection or because it is of very short duration.

      The first phase

      This phase is considered to represent a state of immune tolerance of the virus by the host, permitting its replication usually at very high levels. During this phase, HBeAg is positive, serum HBV DNA levels are very high, HBV infectivity is high but, as already mentioned in the introduction, ALT activity is normal and hepatic histology reveals little if any liver damage. Despite the close link of this immune tolerant phase to vertical HBV transmission in neonates, such a phase can also occur in horizontal HBV transmission from HBeAg positive individuals to toddlers but at significant lower rates (20–30%)
      The duration of the immune tolerant phase is variable. In vertical HBV transmission from HBeAg positive mothers it may last for more than 3 decades while under other conditions as in horizontal HBV spread among children, it appears to be very short and hardly recognizable [
      • Yim H.J.
      • Lok A.S.
      Natural history of chronic hepatitis B virus infection: what we knew in 1981 and what we know in 2005.
      ]. The possible role of the infecting HBV genotypes, racial, nutritional or environmental factors is discussed in a subsequent part of this review.

      The second phase

      The initial immune tolerance phase of HBeAg-positive HBV infection leads to a second phase of immune reactivity against HBV that is implicated pathogenetically in the development of liver necroinflammation and fibrosis. In clinical practice, this phase is referred as HBeAg-positive CHB but the terms immune reactive, immune active, or HBeAg clearance phase are also applied. Serum continues to be HBeAg-positive, HBV DNA levels are usually high but variable, levels of ALT are increased and liver histology reveals necroinflammation with variable stages of fibrosis. The severity, duration, and outcome of this phase and of the underlying liver damage are variable. The annual rate of spontaneous HBeAg clearance in this phase is also variable ranging from 3% to 12% and increases by 2–3 times with interferon alpha (IFN-a) treatment. The phase of HBeAg–positive CHB may end not only in HBeAg seroconversion but also in HBsAg clearance and seroconversion to anti-HBs [
      • Buster E.H.
      • Flink H.J.
      • Cakaloglu Y.
      • Simon K.
      • Trojan J.
      • Tabak F.
      • et al.
      Sustained HBeAg and HBsAg loss after long-term follow-up of HBeAg-positive patients treated with peginterferon alpha-2b.
      ,
      • Hansen B.E.
      • Buster E.H.
      • Steyerberg E.W.
      • Lesaffre E.
      • Janssen H.L.
      Prediction of the response to peg-interferon-alfa in patients with HBeAg positive chronic hepatitis B using decline of HBV DNA during treatment.
      ,
      • Liu J.
      • Yang H.I.
      • Lee M.H.
      • Lu S.N.
      • Jen C.L.
      • Wang L.Y.
      • et al.
      Incidence and determinants of spontaneous hepatitis B surface antigen seroclearance. a community-based follow-up study.
      ]. However, in a number of patients HBV replication continues despite HBeAg loss and the development of anti-HBe antibodies.

      The third phase

      Although the previous phase of immune reactivity against HBV may have unfavorable outcomes with progression of the underlying liver necroinflammation and fibrosis to cirrhosis and even to development of hepatocellular carcinoma (HCC) and death, it largely terminates sooner or later in HBeAg clearance and transition to a third phase during which anti-HBe is positive, there is little residual viral replication and liver histology is essentially normal, except for the presence of “ground-glass” hepatocytes harboring cytoplasmic HBsAg, mainly attributed, as stated, to its expression from HBV DNA sequences integrated into the genome of hepatocytes (Fig. 1). This third phase actually corresponds to the so called “inactive HBsAg carrier state”.

      The reactivation phase

      The previous phase of anti-HBe-positive inactive HBsAg carrier state is not always equivalent with a permanent termination of replication and of HBV-induced chronic liver damage. Although the majority of patients remain for life time in an inactive carrier state and a number of them (around 2% per year) may lose HBsAg and enjoy a complete recovery, others retain or redevelop over time significant HBV replication and progressive liver damage [
      • Bonino F.
      • Rosina F.
      • Rizzetto M.
      • Rizzi R.
      • Chiaberge E.
      • Tardanico R.
      • et al.
      Chronic hepatitis in HBsAg carriers with serum HBV-DNA and anti-HBe.
      ,
      • Hadziyannis S.J.
      • Lieberman H.M.
      • Karvountzis G.G.
      • Shafritz D.A.
      Analysis of liver disease, nuclear HBcAg, viral replication, and hepatitis B virus DNA in liver and serum of HBeAg vs. Anti-HBe positive carriers of hepatitis B virus.
      ,
      • Brunetto M.R.
      • Giarin M.
      • Saracco G.
      • Oliveri F.
      • Calvo P.
      • Capra G.
      • et al.
      Hepatitis B virus unable to secrete e antigen and response to interferon in chronic hepatitis B.
      ,
      • Carman W.F.
      • Jacyna M.R.
      • Hadziyannis S.
      • Karayiannis P.
      • McGarvey M.J.
      • Makris A.
      • et al.
      Mutation preventing formation of hepatitis B e antigen in patients with chronic hepatitis B infection.
      ,
      • Hadziyannis S.J.
      • Papatheodoridis G.V.
      Hepatitis B e antigen-negative chronic hepatitis B: natural history and treatment.
      ,
      • Hadziyannis S.J.
      Hepatitis B e antigen negative chronic hepatitis B: from clinical recognition to pathogenesis and treatment.
      ]. This state of HBV-induced liver damage has been first referred to as “HBeAg-negative/anti-HBe positive chronic hepatitis B” and is considered by most authors as a fourth or reactivation phase in the natural course of chronic HBV infection (Fig. 2). Two representative examples of development of HBeAg-negative CHB after several years of inactivity with normal liver chemistries and anti-HBe positivity are depicted in Fig. 3. HBeAg-negative/anti-HBe-positive CHB being usually a late phase in the course of chronic HBV infection is manifested among relatively older age groups of patients with a mean age difference from HBeAg-positive CHB of 10 or more years [
      • Hadziyannis S.J.
      • Vassilopoulos D.
      Hepatitis B e antigen-negative chronic hepatitis B.
      ]. Its prevalence, initially thought to be low and geographically restricted, has subsequently been reported to increase and spread worldwide. Currently, HBeAg-negative CHB represents the far commonest type of chronic hepatitis B particularly in European, African, and Middle East countries of the Mediterranean Basin [
      • Fattovich G.
      • Bortolotti F.
      • Donato F.
      Natural history of chronic hepatitis B: special emphasis on disease progression and prognostic factors.
      ,
      • Funk M.L.
      • Rosenberg D.M.
      • Lok A.S.
      World-wide epidemiology of HBeAg-negative chronic hepatitis B and associated precore and core promoter variants.
      ,
      • European association for the study of the liver
      EASL clinical practice guidelines: management of chronic hepatitis B.
      ].
      Figure thumbnail gr3
      Fig. 3Two examples of HBeAg-negative/anti-HBe-positive chronic hepatitis B manifested following the inactive HBsAg carrier state of several years duration with normal liver chemistries and positive anti-HBe. In the upper part of the figure anti-HBe-positive liver disease is shown to developed after loss of HBeAg while in the example of the patient depicted in the lower part there was no evidence or history for such a previous HBeAg-positive immune reactive phase phase. Courtesy of Prof. S.J. Hadziyannis.
      As stated in the introduction, HBeAg-negative CHB has been first recognized in 1981 while precore HBV mutants with a G1896A mutation resulting in a novel precore translational stop codon at position 28, preventing HBeAg formation without affecting HBV replication were discovered in 1989. With these molecular/biological findings a convincing answer was given to the burning questions raised by several hepatitis experts of how it is possible for HBV to go on replicating or to reactivate and how can CHB develop despite the loss of HBeAg and in the presence of anti-HBe immunity. In recent reviews [
      • Yim H.J.
      • Lok A.S.
      Natural history of chronic hepatitis B virus infection: what we knew in 1981 and what we know in 2005.
      ,
      • Fattovich G.
      • Bortolotti F.
      • Donato F.
      Natural history of chronic hepatitis B: special emphasis on disease progression and prognostic factors.
      ,
      • Funk M.L.
      • Rosenberg D.M.
      • Lok A.S.
      World-wide epidemiology of HBeAg-negative chronic hepatitis B and associated precore and core promoter variants.
      ] it is clearly stated that understanding the molecular basis of HBV replication in HBeAg-negative patients represents a major milestone in hepatitis B research and in revealing its natural history. Nevertheless, it was only in the 2000s with a delay of two decades, that HBeAg-negative CHB was formally accepted as a phase in the natural course of chronic infection with the wt HBV [
      • Lok A.S.
      • Heathcote E.J.
      • Hoofnagle J.H.
      Management of hepatitis B: 2000–summary of a workshop.
      ,
      • McMahon B.J.
      The natural history of chronic hepatitis B virus infection.
      ].

      Distinct characteristics of the natural history of chronic HBV infection in Euro-Mediterranean and African countries

      As stated above, in European and African countries of the Mediterranean Area, chronic HBV infection and its natural history share a number of features, largely differing from the respective ones prevailing in other geographical areas. These can be summarized as following:
      Vertical transmission in the neonatal period is rare in Euro-Mediterranean countries and all over Africa. The vast majority of chronic HBV infections are acquired horizontally in childhood and are associated with much shorter duration of the first two phases of the natural history of chronic HBV infection. This is at variance from what has been observed in Southeast Asia, where primary HBV infection is frequent not only in neonates but also in infants and children, although in both groups the cumulative duration of the two HBeAg-positive phases is much longer. The annual HBeAg seroconversion rate in South-East Asia is 2% in the first 3 years of life increasing to 4–5% in older children. Almost 90% of infected toddlers still remain HBeAg positive up to the age of 15 years.
      In contrast, in Euro-Mediterranean and African countries only 20–30% of early childhood infections become chronic and only 10% of such chronic infection continue to remain HBeAg-positive during adolescence. The great majority lose HBeAg quickly, at an annual rate of 14–16% [
      • Iorio R.
      • Giannattasio A.
      • Cirillo F.
      • D’ Alessandro L.
      • Vegnente A.
      Long-term outcome in children with chronic hepatitis B: a 24-year observation period.
      ]. Thus, by the second decade of their life the majority of patients are already HBeAg-negative/anti-HBe-positive [
      • Iorio R.
      • Giannattasio A.
      • Cirillo F.
      • D’ Alessandro L.
      • Vegnente A.
      Long-term outcome in children with chronic hepatitis B: a 24-year observation period.
      ,
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Malamitsi-Puchner A.
      • Papacharitonos S.
      • Sotos D.
      • Tzala L.
      • Psichogiou M.
      • Hatzakis A.
      • et al.
      Prevalence study of different hepatitis markers among pregnant Albanian refugees in Greece.
      ]. These geographical differences in the natural history of chronic HBV infection are illustrated in Fig. 5. It is obvious, that in the Euro-Mediterranean area only few women remain HBeAg positive during their reproductive age and this observation largely explains the rarity of perinatal HBV transmission in the same geographical area.
      Figure thumbnail gr5
      Fig. 5Comparison of modes of HBV transmission, annual rates of HBeAg loss and HBeAg positivity in age groups 15–20 and above 40 years, between Euro-Mediterranean and African countries vs Southeast Asia countries. Compilation of data from [
      • Yim H.J.
      • Lok A.S.
      Natural history of chronic hepatitis B virus infection: what we knew in 1981 and what we know in 2005.
      ,
      • Liaw Y.F.
      • Brunetto M.R.
      • Hadziyannis S.J.
      The natural history of chronic HBV infection and geographical differences.
      ,
      • Fattovich G.
      Natural history and prognosis of hepatitis B.
      ,
      • Iorio R.
      • Giannattasio A.
      • Cirillo F.
      • D’ Alessandro L.
      • Vegnente A.
      Long-term outcome in children with chronic hepatitis B: a 24-year observation period.
      ,
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Malamitsi-Puchner A.
      • Papacharitonos S.
      • Sotos D.
      • Tzala L.
      • Psichogiou M.
      • Hatzakis A.
      • et al.
      Prevalence study of different hepatitis markers among pregnant Albanian refugees in Greece.
      ,
      • Chu C.M.
      • Liaw Y.F.
      Chronic hepatitis B virus infection acquired in childhood: special emphasis on prognostic and therapeutic implication of delayed HBeAg seroconversion.
      ].
      Not only the initial immune tolerant phase but also the subsequent immune active phase of HBeAg clearance (Fig. 2) is short and usually non-recognizable in patients from countries of the Mediterranean Basin (37–39) and Africa. Moreover, the rates of development of advanced liver disease, cirrhosis, and HCC in HBeAg-positive patients are significantly lower compared to Asiatic and other countries, probably because of its shorter duration [
      • Fattovich G.
      • Bortolotti F.
      • Donato F.
      Natural history of chronic hepatitis B: special emphasis on disease progression and prognostic factors.
      ]. The third phase of the inactive HBsAg carrier state with immune control of the infection is usually reached during adolescence being in contrast to the much older age of the respective phase in other countries particularly from Asia.
      In the Euro-Mediterranean and African area the great majority (>85%) of patients with biochemically and histologically active disease are HBeAg-negative whereas in Asia, North Europe, and the USA, HBeAg-positive CHB predominates. The mean age of patients with HBeAg-negative CHB is much older compared to the age of HBeAg-positive ones in the same area [
      • Hadziyannis S.J.
      Hepatitis B e antigen negative chronic hepatitis B: from clinical recognition to pathogenesis and treatment.
      ,
      • Hadziyannis S.J.
      • Vassilopoulos D.
      Hepatitis B e antigen-negative chronic hepatitis B.
      ]. These age data taken together with the short duration in the Mediterranean area of the immune reactive HBeAg-positive phase, suggest that the development of HBeAg-negative CHB is largely linked to the reactivation of HBV in “inactive” HBsAg carriers rather than with an ongoing HBV replication in continuation of the second phase of HBeAg-positive CHB patients, despite the loss of HBeAg and seroconversion to anti-HBe [
      • Fattovich G.
      • Bortolotti F.
      • Donato F.
      Natural history of chronic hepatitis B: special emphasis on disease progression and prognostic factors.
      ,
      • Hadziyannis S.J.
      • Papatheodoridis G.V.
      Hepatitis B e antigen-negative chronic hepatitis B: natural history and treatment.
      ,
      • Hadziyannis S.J.
      Hepatitis B e antigen negative chronic hepatitis B: from clinical recognition to pathogenesis and treatment.
      ,
      • Hadziyannis S.J.
      • Vassilopoulos D.
      Hepatitis B e antigen-negative chronic hepatitis B.
      ]. The frequency of cirrhosis and of HCC are quite high in HBeAg-negative CHB patients and increase significantly with their age [
      • Fattovich G.
      • Bortolotti F.
      • Donato F.
      Natural history of chronic hepatitis B: special emphasis on disease progression and prognostic factors.
      ,
      • Kew M.C.
      Hepatitis viruses and hepatocellular carcinoma.
      ]. In long term follow-up studies of Asian patients, it has recently been reported that the older the age at spontaneous HBeAg seroconversion, the higher are the rates of development of HBeAg-negative CHB, of cirrhosis, and of HCC. Thus, in patients who lost HBeAg after the age of 40 years, the 15 year cumulative incidence of HBeAg-negative CHB, of cirrhosis, and HCC reached 66.7%, 42.9%, and 7.7%, respectively [
      • Chen Y.C.
      • Chu C.M.
      • Liaw Y.F.
      Age-specific prognosis following spontaneous hepatitis B e antigen seroconversion in chronic hepatitis B.
      ].
      The development of HCC in younger age groups of HBsAg-positive HBeAg-negative patients in the absence of cirrhosis documented in several areas of Africa particularly in Sub-Saharan countries [
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Kew M.C.
      Hepatitis viruses and hepatocellular carcinoma.
      ] will be discussed in the context of implicated factors particularly of HBV subgenotypes.
      Finally, the annual rates of spontaneous HBsAg clearance in the Mediterranean basin appear to be close to 1% in childhood and adolescence [
      • Iorio R.
      • Giannattasio A.
      • Cirillo F.
      • D’ Alessandro L.
      • Vegnente A.
      Long-term outcome in children with chronic hepatitis B: a 24-year observation period.
      ] and to increase to 1.5–2.0% in older age groups [
      • Fattovich G.
      • Bortolotti F.
      • Donato F.
      Natural history of chronic hepatitis B: special emphasis on disease progression and prognostic factors.
      ,
      • Hadziyannis E.
      • Sevastianos V.
      • Georgiou A.
      • Hadziyannis S.J.
      Treatment-related compared to spontaneously-occurring HBsAg loss in HBeAg-negative chronic hepatitis B.
      ]. These rates appear to be significantly higher compared to those reported in countries of Southeast Asia and of other geographical areas. However, the annual rates of HBsAg clearance in these countries may have been underestimated since in more recent studies of longer follow-up extending to >20 years after HBeAg seroconversion, the HBsAg clearance rate has been found to increase approximately to 2% [
      • Chu C.M.
      • Liaw Y.F.
      HBsAg seroclearance in asymptomatic carriers of high endemic areas: appreciably high rates during a long-term follow-up.
      ].

      Implicated factors

      A number of variables appear to be pathogenetically implicated in the evolution of the natural history of chronic HBV infection in Mediterranean and African countries.

      Level of HBV endemicity

      It is assumed that high levels of HBV endemicity in a community correlates with a higher frequency of exposure to acute (primary) HBV infection in early life which has the effect of determining the rates of development of chronic HBV infection as well several aspects of its natural history. This does not appear to be the case in European, African as well as in Near and Middle East countries of the Mediterranean Basin. Although the level of HBV endemicity is intermediate (varying between 2% and 8%, Fig. 2); regions and foci of high, as well as, of low HBV endemicity have been identified within the same country. Furthermore, while a significant decrease in the prevalence of HBsAg at least in certain countries like Greece, Italy, and Spain has occurred over the years, in many areas of Africa, HBV endemicity remains high. Despite these variations in HBV endemicity between Euro-Mediterranean and African regions and countries, the overall features of the natural history of chronic HBV infection are strikingly similar: HBV infection of neonates is rare, primary infection with transition to chronicity is restricted to infancy and childhood; and is followed by early loss of HBeAg and by striking predominance of anti-HBe-positive CHB. This is true also for the high HBV endemicity areas of Africa except for the development of HCC at a much younger age [
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Kew M.C.
      Hepatitis viruses and hepatocellular carcinoma.
      ].
      Although the socioeconomic and hygiene level, local conditions, and habits of the studied populations as well as genetic and environmental factors may also play a role, it is now becoming evident that the natural history of chronic HBV infection is mainly determined by viral factors. HBV genotypes, sub-genotypes, and specific mutations of the HBV genome are currently implicated for similarities and differences in its natural history and the development of severe chronic liver disease and particularly of HCC.

      Age and modes of viral transmission

      The age at acquisition of hepatitis B and its modes of transmission have already been discussed. However, it is important to stress that the use of non-disposable needles and syringes for vaccination and other purposes has been implicated in Greece, Italy, and in African countries. Moreover contrary to the situation in South East Asia where vertical transmission from HBeAg positive mothers to neonates predominated, at least in the pre-vaccination era [
      • Kew M.C.
      Hepatitis viruses and hepatocellular carcinoma.
      ], this has not been the case of HBV spread in the Mediterranean Basin as well as all over Africa (66). This can be explained by the fact that few of HBV infected mothers fulfill the prerequisite for vertical HBV transmission of HBeAg positivity. Several large epidemiological studies in the Mediterranean basin and Africa have showed that <5% of HBsAg positive young adults and of women in their reproductive age are HBeAg positive [
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Malamitsi-Puchner A.
      • Papacharitonos S.
      • Sotos D.
      • Tzala L.
      • Psichogiou M.
      • Hatzakis A.
      • et al.
      Prevalence study of different hepatitis markers among pregnant Albanian refugees in Greece.
      ].

      HBV genotypes

      From 2000 and on, HBV genotypes and subgenotypes have attracted a lot of clinical and research interest and are currently considered as determinants and/or predictors of the natural history of HBV infection, the severity of HBV-induced liver disease and of the risk of HCC development. In this context a number of relevant clinical and molecular studies [
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Kao J.H.
      Hepatitis B viral genotypes: clinical relevance and molecular characteristics.
      ,
      • Kew M.C.
      • Kramvis A.
      • Yu M.C.
      • Arakawa K.
      • Hodkinson J.
      Increased hepatocarcinogenic potential of hepatitis B virus genotype A in Bantu-speaking sub-saharan Africans.
      ,
      • Kramvis A.
      • Kew M.
      • Francois G.
      Hepatitis B virus genotypes.
      ,
      • Tanaka Y.
      • Hasegawa I.
      • Kato T.
      • Orito E.
      • Hirashima N.
      • Acharya S.K.
      • et al.
      A case-control study for differences among hepatitis B virus infections of genotypes A (subtypes Aa and Ae) and D.
      ] have been recently reviewed [
      • Hadziyannis S.
      • Le Bouvier G.L.
      Australia antigen subtypes in Greece.
      ].
      In the Mediterranean Basin there is an impressive overall predominance of HBV genotype D (Fig. 4) that also extends to other neighboring countries [
      • Norder H.
      • Courouce A.M.
      • Coursaget P.
      • Echevarria J.M.
      • Lee S.D.
      • Mushahwar I.K.
      • et al.
      Genetic diversity of hepatitis B virus strains derived worldwide: genotypes, subgenotypes, and HBsAg subtypes.
      ]. In the early 1970s, when HBV genotypes had not yet been identified, Hadziyannis and LeBouvier [
      • Hadziyannis S.
      • Le Bouvier G.L.
      Australia antigen subtypes in Greece.
      ] conducted a large study of HBsAg subtypes in acute and chronic HBV infection in Greece and found higher than 90% predominance of subtypes ayw2 and ayw3. These serotypes are now known to correspond to HBV genotype D. Genotype D predominance all over the Mediterranean area (Fig. 4) has been found in some regions to account for more than 80% and even >90% of HBV infections [
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Kurbanov F.
      • Tanaka Y.
      • Mizokami M.
      Geographical and genetic diversity of the human hepatitis B virus.
      ].
      Figure thumbnail gr4
      Fig. 4Geographical map displaying the levels of HBV endemicity in the world and the areas of predominance of the various HBV genotypes. The overall level of HBV endemicity in the Mediterranean basin in this map is intermediate but differs significantly from country to country. In the Euro-Mediterranean countries current median HBV endemicity levels are below 3%. Data have been compiled and adapted from references [
      • Liaw Y.F.
      • Brunetto M.R.
      • Hadziyannis S.J.
      The natural history of chronic HBV infection and geographical differences.
      ,
      • Kurbanov F.
      • Tanaka Y.
      • Mizokami M.
      Geographical and genetic diversity of the human hepatitis B virus.
      ].
      The other HBsAg serotype that has been detected in the Mediterranean area in the 1970s is adw and corresponds to genotype A. In Greece it accounted for approximately 5% of the overall cases of HBV infection and this low prevalence has remained unchanged over the years [
      • Dimou E.
      • Rapti I.
      • Kostamena A.
      • Laras A.
      • Hadziyannis S.J.
      Development of precore and basic core promoter HBV mutations in chronic hepatitis B genotypes D and A. Aprospective study in a Caucasian population.
      ]. Genotype A prevails in some countries of North Europe and in South Africa.
      In the Mediterranean and surrounding countries of high genotype D predominance, there is a similarly impressive predominance of HBeAg-negative precore mutant CHB. A similar association exists between HBeAg-negative CHB and genotype E in Central and West African countries. The molecular characteristics of HBV genotypes D and E that determine HBeAg loss are the same but different from those of genotype A and of its subgenotypes [
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Tanaka Y.
      • Hasegawa I.
      • Kato T.
      • Orito E.
      • Hirashima N.
      • Acharya S.K.
      • et al.
      A case-control study for differences among hepatitis B virus infections of genotypes A (subtypes Aa and Ae) and D.
      ,
      • Kurbanov F.
      • Tanaka Y.
      • Mizokami M.
      Geographical and genetic diversity of the human hepatitis B virus.
      ].
      The nucleotide harbored at position 1858 in genotypes D and E is T, and the G1896A mutation, which develops during the course of chronic HBV infection where it prevents the formation of HBeAg, creates a strong T-A bond that stabilizes the stem of the epsilon (ε) encapsidation signal of the virus [
      • Hadziyannis S.J.
      • Vassilopoulos D.
      Hepatitis B e antigen-negative chronic hepatitis B.
      ]. This is actually true for all HBV genotypes with T at position 1858, while in the case of HBV genotype A the nucleotide harbored at 1858 is C, and this precludes the development of a stable precore translational stop codon unless a C1858T mutation also develops. Therefore, it is not surprising that HBeAg-negative CHB rarely, if ever, develops in infections with HBV genotype A at least when a European strain of genotype A is involved [
      • Dimou E.
      • Rapti I.
      • Kostamena A.
      • Laras A.
      • Hadziyannis S.J.
      Development of precore and basic core promoter HBV mutations in chronic hepatitis B genotypes D and A. Aprospective study in a Caucasian population.
      ].
      In contrast to the Mediterranean area and West and Central Africa where genotypes D and E prevail, (Fig. 4) genotype A is the predominant genotype in sub-Saharan countries and South Africa [
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ]. In these areas HBeAg loss occurs early in the natural course of HBV infection and HCC develops in younger age groups even in the absence of cirrhosis [
      • Kew M.C.
      Hepatitis viruses and hepatocellular carcinoma.
      ]. These geographical variations seem to be explained by differences in the molecular characteristics of HBV genotype A of African and European strains compared to genotype D [
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Tanaka Y.
      • Hasegawa I.
      • Kato T.
      • Orito E.
      • Hirashima N.
      • Acharya S.K.
      • et al.
      A case-control study for differences among hepatitis B virus infections of genotypes A (subtypes Aa and Ae) and D.
      ,
      • Kurbanov F.
      • Tanaka Y.
      • Mizokami M.
      Geographical and genetic diversity of the human hepatitis B virus.
      ].

      HBV subgenotypes

      HBV genotypes differ by >8% in the overall sequence of the HBV genome and by >4% in the sequences of the surface gene [
      • McMahon B.J.
      The natural history of chronic hepatitis B virus infection.
      ,
      • Kao J.H.
      Role of viral factors in the natural course and therapy of chronic hepatitis B.
      ,
      • Lin C.L.
      • Kao J.H.
      Hepatitis B viral factors and clinical outcomes of chronic hepatitis B.
      ]. Geographical similarities in the prevailing HBV genotypes may extend or not to their subgenotypes. In the case of genotype D, the same subgenotypes appear to prevail in the Mediterranean area and the surrounding countries. On the other hand, in the case of genotype A there are significant differences between subgenotype A2 (or Ae) that prevails in Europe and subgenotype A1 (or Aa) that predominates in Africa. In fact the African subgenotype A1 has molecular characteristics that appear to determine early HBeAg clearance by prevention of its formation both at the transcriptional and translational level; while in infection with the European subgenotype A2, HBeAg loss is linked to development of mutations acting only at the transcriptional level. Such mutations are neither stable nor associated with the development of anti-HBe positive CHB [
      • Buster E.H.
      • Flink H.J.
      • Cakaloglu Y.
      • Simon K.
      • Trojan J.
      • Tabak F.
      • et al.
      Sustained HBeAg and HBsAg loss after long-term follow-up of HBeAg-positive patients treated with peginterferon alpha-2b.
      ]. Thus, data on HBV genotypes and subgenotypes in the geographical area of the Mediterranean basin extending to those in the surrounding countries and in Central and South Africa, may account for and explain a number of associated similarities and differences in the natural course and clinical outcomes of chronic HBV infection.
      The African subgenotype A1 is found in S. Africa, Malawi, Uganda, Tanzania, Somalia, and Yemen [
      • Liaw Y.F.
      • Brunetto M.R.
      • Hadziyannis S.J.
      The natural history of chronic HBV infection and geographical differences.
      ,
      • Kramvis A.
      • Kew M.C.
      Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes.
      ,
      • Kurbanov F.
      • Tanaka Y.
      • Mizokami M.
      Geographical and genetic diversity of the human hepatitis B virus.
      ]. Compared to the European Ae, Aa is much less frequently HBeAg+ (33% vs 67%) and is associated with lower HBV DNA levels (3.5 vs 6.1 log copies/ml); moreover, its characteristics at the molecular level are compatible with the observed early and durable HBeAg loss and seroconversion to anti-HBe [
      • Kramvis A.
      • Kew M.
      • Francois G.
      Hepatitis B virus genotypes.
      ,
      • Tanaka Y.
      • Hasegawa I.
      • Kato T.
      • Orito E.
      • Hirashima N.
      • Acharya S.K.
      • et al.
      A case-control study for differences among hepatitis B virus infections of genotypes A (subtypes Aa and Ae) and D.
      ]. It harbors a double substitution at T1809 and T1812 (100% and 96%) upstream of the precore initiation codon which interferes with the translation of HBeAg. This substitution has not been detected in any of 57 Ae isolates. Furthermore, the hepatocarcinogenetic potential of the African subgenotype A1 appears to be greater than that of other genotypes in the same geographical area. Thus, in Sub-Saharan Bantu speaking Africans, HBV-related HCC has been found to be almost entirely attributable to subgenotype A1 [
      • Kew M.C.
      • Kramvis A.
      • Yu M.C.
      • Arakawa K.
      • Hodkinson J.
      Increased hepatocarcinogenic potential of hepatitis B virus genotype A in Bantu-speaking sub-saharan Africans.
      ,
      • McMahon B.J.
      The influence of hepatitis B virus genotype and subgenotype on the natural history of chronic hepatitis B.
      ,
      • Neuveut C.
      • Wei Y.
      • Buendia M.A.
      Mechanisms of HBV-related hepatocarcinogenesis.
      ]. In recent studies several mutations affecting the X gene of HBV identified in subgenotype A1 have been implicated in the early development of HCC in Africa. Moreover, since the African HBV subgenotype A1 has also been exported to other geographical areas and has already been detected in European countries (Italy, Spain, France) it is intriguing to evaluate whether the outcome of chronic HBV infection with HBV genotype A1 vs genotype A2 differs under the same nutritional and environmental factors.
      On the basis of the above data many more studies on the molecular and biological aspects of HBV and its genotypes, subgenotypes, and the development of mutations in the course of HBV infection, are recommendable in appropriate populations and cohorts of patients [
      • McMahon B.J.
      Natural history of chronic hepatitis B.
      ].

      Conclusions and perspectives

      The natural history of chronic HBV infection in Euro-Mediterranean and African countries is characterized by many similarities in the evolution, duration, and outcome of its phases. The Mediterranean characteristics of its natural course differ significantly from the respective ones in other geographical areas of the world. It is now becoming obvious that similarities and differences in the natural history of HBV infection are largely linked to the molecular characteristics of the prevailing HBV genotypes and subgenotypes. Host and environmental factors may also contribute to a shorter or longer natural history and to the rate of development and severity of HBV-induced chronic liver disease particularly HCC. Appropriate long term studies are needed to clarify the specific role played by numerous viral, host, environmental, and other factors and their interplay in the natural course of chronic hepatitis B and in the rate and time of development of severe liver disease and HCC. Relevant information is expected to determine the best monitoring strategies to be applied in clinical practice aiming at early recognition and treatment.
      Figure thumbnail fx1

      Conflict of interest

      The author declared that he does not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.

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