A total of 2229 children selected from five distinct areas of Thailand were screened for HBs antigen (HBsAg) by ELISA. Out of 51, forty-nine HBsAg-positive children were further examined for HBV-DNA by the polymerase chain reaction, utilizing the region of the hepatitis B Virus (HBV) genome encoding the major antigenic epitopes of hepatitis B surface antigen. Direct automated sequencing of the "a" determinant region revealed 11 of 49 children to display variable mutations. The vaccinated and nonvaccinated children had amino acid variants clustered between residues 120 and 160. Mutations between residues 120 and 160 were found at higher frequency in the vaccinated group (4/13; 30.8%) than in the nonvaccinated group (7/36; 19.4%), but this was not statistically significant. Infections with new HBV variants are contracted either vertically or horizontally within the group having received the vaccine, a finding confirmed by the presence of amino acid substitutions critical for immune escape. Hence, neither vaccine nor IgG has any apparent effect on those variants and the children turn into HBV carriers. However, the current vaccination program still efficiently protects perinatal transmission of HBV and unless long term studies lead us to conclude otherwise, inclusion of the variant strain(s) into a new vaccine formulation is not deemed necessary.
As hepatitis A virus (HAV) is usually transmitted through the faecal-oral route, hepatitis A is a communicable disease. In countries of intermediate to low endemicity, sudden outbreaks of human infection with the virus may occur. Between September 2001 and April 2002, there were two outbreaks of HAV infection in the Ruso and Yeengor districts of Narathiwas province, in southern Thailand. Isolates of HAV were recovered during these outbreaks, from 14 in-patients with acute hepatitis in Ruso (12 positive for anti-HAV IgM and all positive for HAV RNA), 16 children with asymptomatic infection in Yeengor (14 positive for anti-HAV IgM and nine for HAV RNA), and four isolated cases in Bangkok (all positive for anti-HAV IgM). Molecular characterization of the VP1-P2A region of each isolate was followed by phylogenetic analysis. All of the isolates from Narathiwas province were found to be of genotype 1a, to have the same VP1 nucleotide sequence, and to show a high level of sequence homology (>/= 99.5%) with the isolates from Bangkok and with previous Thai isolates. These results should facilitate further research into HAV transmission and genotype identification in community outbreaks.
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