Despite the availability of an effective vaccine and drugs that can suppress viral replication, hepatitis B virus (HBV) continues to impose an enormous global health burden. Over 240 million individuals are chronically HBV infected worldwide, causing chronic hepatitis and hepatocellular carcinoma. HBV is classified into genotypes based on genetic diversity. The predominant genotype in West Africa, genotype E (GT/E), is generally not found elsewhere in the world however isolated cases resulting from spread directly from Africa are now being identified. HBV GT/E has low genetic diversity, a short evolutionary history, yet in less than 200 years has become the predominant HBV genotype in West Africa. With the rapid emergence of HBV GT/E in Africa and the inevitability of its spread to other continents, there is a public health urgency to understand the biology of HBV GT/E. The current HBV vaccines consist of HBsAg derived from genotype A2. Likewise, many commercial HBV screening assays utilize antibodies directed against HBsAg. Mutations in the S gene can lead to failure of commercial assays to detect HBsAg and vaccine resistance. Potentially relevant to the rapid spread of HBV GT/E high rates of ?occult disease? (HBsAg- /HBV viremia +) have been described in West Africa as well as simultaneous detection of both HBsAg and anti-HBs. Notably, HBV GT/E has a consensus mutation in the pre- S1 region introducing a new start codon; it is not known if this results in a novel S polypeptide and/or impairs translation of the other S proteins, but in total these findings raise concern that variations in S gene expression of HBV GT/E may alter host recognition, reduce efficacy of diagnostic assays and/or avoid vaccine protection. Because several lines of evidence suggest that HBV GT/E is of public health concern, yet we know nothing about the biology of this new genotype or its relationship with the host vaccine response, detection by standard assays, and other HBV genotypes, we proposes to create the necessary HBV GT/E experimental systems and investigate the biology of HBV GT/E in order to assess the risk this new HBV genotype poses to public health. Broadly, we hypothesize that HBV GT/E may have a selective advantage over other HBV genotypes. Specifically, we hypothesize that either consensus sequence differences in the S gene region of HBV GT/E may lead to altered to expression of the HBV S genes, changes in the S proteins that evade vaccine induced antibody recognition or perhaps that it can out compete other HBV genotypes due to more efficient replication and/or spread. To test these hypotheses, we propose 3 specific aims: 1) Elucidate the impact of HBV GT/E S region consensus sequence differences on S protein expression and immunogenicity; 2) Determine whether HBV GT/E replication / infection is more robust that other HBV genotypes;3) Identify the frequency of HBV GT/ E viremia in vaccinated individuals from the West African country Ghana.
Over 240 million individuals are chronically HBV infected worldwide, causing chronic hepatitis and hepatocellular carcinoma. Several lines of evidence suggest that HBV genotype E, which has rapidly emerged in West Africa and is now spreading to other continents, is of public health concern yet we know nothing about the biology of HBV GT/E or its relationship with the host vaccine response, detection by standard assays, and other HBV genotypes. Hence, we propose to create the necessary HBV GT/E experimental systems and investigate the biology of HBV GT/E in order to assess the risk this new HBV genotype poses to public health.
