Molecular characterization of subgenotype A1 (subgroup Aa) of hepatitis B virus

Exceptional genetic variability of hepatitis B virus indicates that Rwanda is east of an emerging African genotype E/A1 divide

In Western Africa, hepatitis B virus (HBV) genotype E predominates throughout a vast crescent spanning from Senegal to Namibia and at least to the Central African Republic to the East. Although from most of the eastern parts of sub-Saharan Africa only limited sets of strains have been characterized, these belong predominantly to genotype A. To study how far the genotype E crescent extends to the East, a larger number of HBV strains from Rwanda were analyzed. Phylogenetic analysis of 45 S fragment sequences revealed strains of genotypes A (n = 30), D (n = 10), C (n = 4), and B (n = 1). Twelve genotype A sequences formed a new cluster clearly separated from the reference strains of the known sub-genotypes. Thus, with four genotypes and at least six sub-genotypes and a new cluster of genotype A strains, HBV shows an exceptional genetic variability in this small country, unprecedented in sub-Saharan Africa. Despite this exceptional genetic variability, not a single genotype E virus was found indicating that this country does not belong to the genotype E crescent, but is east of an emerging African genotype E/A1 divide.

Genotype D amongst injection drug users with acute hepatitis B virus infection in British Columbia

The eight genotypes of hepatitis B virus (HBV) exhibit distinct geographical distributions. This study identified HBV genotypes and transmission modes associated with acute infection in British Columbia (BC), Canada, from 2001 to 2005. Seventy cases of acute HBV in BC were identified from laboratory reports using a standardized case definition. Interviews for risk factors and hepatitis history were conducted for each case. HBV genotypes were determined by BLAST comparison analysis of the surface (S) or preS gene sequence. To illustrate the distribution of genotypes identified amongst acute cases in BC, an annotated map was produced showing the global occurrence of HBV genotypes. The majority of acute HBV cases occurred in Caucasian, Canadian-born males, with 30% of cases reporting injection drug use (IDU) and 21% reporting incarceration. The most common genotype observed was genotype D (62.9%), followed by genotypes A (18.6%), C (11.4%), B (4.3%), and E (1.4%). A significant association was observed between Genotype D and IDU (P = 0.0025) and previous incarceration (P = 0.0067). Phylogenetic analysis of the S gene sequence demonstrated identical or high genetic relatedness amongst genotype D viral strains (86% sub-genotype D3), thus verifying transmission clustering amongst BC injection drug users. The association between acute HBV genotype and reported transmission modes has not been previously described in North America. Tracking of genotypes can help identify disease transmission patterns and target at-risk populations for preventive immunization.

A valine to phenylalanine mutation in the precore region of hepatitis B virus causes intracellular retention and impaired secretion of HBe-antigen

AIM

Hepatitis B virus (HBV) e antigen (HBeAg) is translated from precore mRNA as a precore/core protein, which is post-translationally modified to give rise to the protein that is secreted into the serum. The G1862T mutation in HBV occurs in the bulge of the encapsidation signal within the pregenomic RNA. When the precore mRNA is translated, this mutation results in a valine to phenylalanine substitution at the -3 position to the signal peptide cleavage site at the amino end of the precursor protein. The aim of this study was to determine whether this mutation could affect HBV replication and/or HBeAg expression.

METHODS

Following transfection of Huh 7 cells, HBV replication was followed using real time polymerase reaction (PCR) and expression of HBeAg expression was monitored using confocal microscopy.

RESULTS

HBV replication was reduced when this mutation was introduced into genotype D but not into genotype A replication-competent constructs. Using mutant HBeAg-expressing plasmids, we demonstrated a 54% reduction in HBeAg secretion relative to the wild type. Confocal microscopy demonstrated that the mutant HBeAg accumulated in the endoplasmic reticulum, endoplasmic reticulum intermediate compartment and Golgi. These aggregates of mutant protein increased in size following treatment of the cells with a proteasome inhibitor, MG132, and had the hallmark features of aggresomes. They attracted ubiquitin, heat shock proteins and proteasomes and were isolated from the cytosol by the intermediate filaments, vimentin and cytokeratin.

CONCLUSION

The formation of aggresomes, as a result of the G1862T mutation, may play a contributory role in HBV-induced liver disease.

Epidemiology of hepatitis B virus in Africa, its genotypes and clinical associations of genotypes

Of approximately 360 million people in the world chronically infected with hepatitis B virus (HBV), 65 million reside in Africa. Thus, Africa, with 12% of the world's population, carries approximately 18% of the global burden of HBV infection, with hepatocellular carcinoma and cirrhosis accounting for 2% of the continent's annual deaths. Despite HBV being endemic or hyperendemic in Africa, there is a paucity of data on the genotypes and their distribution. Genotype A is found mainly in southern, eastern and central Africa. Most African genotype A strains belong to subgenotype A1, with subgenotype A3 found in western Africa. Genotype D prevails in northern countries and genotype E in western and central Africa. Ithas become increasingly evident that heterogeneity in the global distribution of HBV genotypes may be responsible for differences in the clinical outcomes of HBV infections and the response to antiviral treatment and vaccination. A limited number of studies have been published relating genotypes to clinical outcomes in African countries. Because observations from other regions of the world can not be extrapolated from one locale to another, the HBV strains circulating in Africa should be studied and related to clinical outcomes.