PO 8275 HEPATITIS B VIRUS IMMUNE ESCAPE MUTANTS AMONG APPARENTLY HEALTHY INHABITANTS IN IBADAN, SOUTHWESTERN NIGERIA

BackgroundThe documentation of circulation of immune escape mutants (IEMs) poses a risk on the continual success of HBV prevention and control. Therefore, this study aimed to determine the possible circulation of IEM among asymptomatic dwellers in southwestern Nigeria.MethodsBlood samples collected from consenting 133 males and 305 female participants in Ibadan were tested for HBsAg, HBeAg, HBcIgM, HBcTotal and HBsAb by ELISA technique. Samples positive for HBsAg were further analysed for HBV DNA by amplifying and sequencing the S gene. Isolates were genotyped and subtyped based on amino acid residues at position 122, 127, 134, 160 of the S gene.ResultsOf the 438 subjects tested 31 (7.1%) were positive for HBsAg, 2 (6.5%) of which were HBeAg positive. Ninety-nine (22.8%) had detectable HBsAb, 3 (0.7%) were positive for HBcIgM and 195 (44.5%) were HBcTotal positive. HBV DNA was amplified and sequenced in 27 out of 31 and 4 could not be amplified due to low titres. After sequencing, 9 (33.3%) were not exploitable due to the presence of multiple peaks. Of the 18 exploitable isolates, only 15 showed significant similarity to HBV S-gene. Eleven of the 15 isolates were subtyped as ayw4 while others could not due to substitution at s122p. Phylogram showed that the 11 isolates were genotype E. Two of the 4 isolates with R122Q/P substitutions also belonged to genotype E while the other 2 which were >11% divergent from the reference genotype E sequence clustered with an isolate previously described as an Immune Escape Mutant.ConclusionThis study identified high endemicity of HBV infection, presence of markers of infection even in non-detectable HBsAg levels and circulation of genotype E ayw4 and vaccine mutants in south-western Nigeria. It therefore emphasises the risk of development of an indigenous infected population that may not be protected by the current vaccine.

Occult Hepatitis B Virus Infection among HIV Positive Patients in Nigeria

HIV has been known to interfere with the natural history of hepatitis B virus (HBV) infection. In this study we investigate the prevalence of occult hepatitis B virus infection (OBI) among HIV-infected individuals in Nigeria. Overall, 1200 archived HIV positive samples were screened for detectable HBsAg using rapid technique, in Ikole Ekiti Specialist Hospital. The HBsAg negative samples were tested for HBsAg, anti-HBc, and anti-HCV by ELISA. Polymerase chain reaction was used for HBV DNA amplification and CD4 counts were analyzed by cytometry. Nine hundred and eighty of the HIV samples were HBsAg negative. HBV DNA was detected in 21/188 (11.2%) of patients without detectable HBsAg. CD4 count for the patients ranged from 2 to 2,140 cells/μL of blood (mean = 490 cells/μL of blood). HCV coinfection was detected only in 3/188 (1.6%) of the HIV-infected patients (P>0.05). Twenty-eight (29.2%) of the 96 HIV samples screened were positive for anti-HBc. Averagely the HBV viral load was <50 copies/mL in the OBI samples examined by quantitative PCR. The prevalence of OBI was significantly high among HIV-infected patients. These findings highlight the significance of nucleic acid testing in HBV diagnosis in HIV patients.

High genetic variability of the group-specific a-determinant of hepatitis B virus surface antigen (HBsAg) and the corresponding fragment of the viral polymerase in chronic virus carriers lacking detectable HBsAg in serum

Chronic carriers of hepatitis B virus (HBV) usually show hepatitis B surface antigen (HBsAg) in their sera, which is considered the best marker for acute and chronic HBV infection. In some individuals, however, this antigen cannot be detected by routine serological assays despite the presence of virus in liver and peripheral blood. One reason for this lack of HBsAg might be mutations in the part of the molecule recognized by specific antibodies. To test this hypothesis, the HBV S gene sequences were determined of isolates from 33 virus carriers who were negative for HBsAg but showed antibodies against the virus core (anti-HBc) as the only serological marker of hepatitis B. Isolates from 36 HBsAg-positive patients served as controls. In both groups, a considerable number of novel mutations were found. In isolates from individuals with anti-HBc reactivity only, the variability of the major hydrophilic loop of HBsAg, the main target for neutralizing and diagnostic antibodies, was raised significantly when compared with the residual protein (22·6 vs 9·4 mutations per 1000 amino acids; P<0·001) and with the corresponding region in the controls (22·6 vs 7·5 exchanges per 1000 residues; P<0·001). A similar hypervariable spot was identified in the reverse transcriptase domain of the viral polymerase, encoded by the same nucleotide sequence in an overlapping reading frame. These findings suggest that at least some of the chronic low-level carriers of HBV, where surface antigen is not detected, could be infected by diagnostic escape mutants and/or by variants with impaired replication.