Genotype E: The neglected genotype of hepatitis B virus

Abstract

Hepatitis B virus (HBV) (sub)genotypes A1, D3 and E circulate in sub-Saharan Africa, the region with one of the highest incidences of HBV-associated hepatocellular carcinoma globally. Although genotype E was identified more than 20 years ago, and is the most widespread genotype in Africa, it has not been extensively studied. The current knowledge status and gaps in its origin and evolution, natural history of infection, disease progression, response to antiviral therapy and vaccination are discussed. Genotype E is an African genotype, with unique molecular characteristics that is found mainly in Western and Central Africa and rarely outside Africa except in individuals of African descent. The low prevalence of this genotype in the African descendant populations in the New World, phylogeographic analyses, the low genetic diversity and evidence of remnants of genotype E in ancient HBV samples suggests the relatively recent re-introduction into the population. There is scarcity of information on the clinical and virological characteristics of genotype E-infected patients, disease progression and outcomes and efficacy of anti-HBV drugs. Individuals infected with genotype E have been characterised with high hepatitis B e antigen-positivity and high viral load with a lower end of treatment response to interferon-alpha. A minority of genotype E-infected participants have been included in studies in which treatment response was monitored. Of concern is that current guidelines do not consider patients infected with genotype E. Thus, there is an urgent need for further large-scale investigations into genotype E, the neglected genotype of HBV.

Keywords: Antiviral therapy; Clinical significance; Evolution; Genotype E; Hepatitis B virus; Vaccination.

Figure 1

Organizational structure of hepatitis B virus genotype E genome. The hepatitis B virus genome consists of a partially double stranded DNA with the complete minus strand and the incomplete strand. The four open reading frames are shown: precore/core (preC/C) that encodes the e antigen (HBeAg) and core protein (HBcAg); POL for polymerase (reverse transcriptase), preS1/preS2/S for surface proteins (three forms of HBsAg, small, middle and large) and X for a transcriptional trans-activator protein. The promoters, enhancers and the unique restriction enzymes are shown.