Phylogenetic relatedness and genetic diversity of hepatitis B virus isolates in Eastern India.

Hepatitis B virus (HBV) has been classified into eight genotypes, and several subgenotypes, distinctly distributed geographically. The genotypes A and D were previously reported to be predominant in India. Recent studies indicated evidence of circulation of genotype C in Eastern part of India. With the aim to confirm the phylogenetic relation and molecular genetic characteristics of the HBV circulating in Kolkata, the most populous city in Eastern India, 11 strains were isolated and the complete genome sequences were analyzed. Phylogenetic analysis determined; three genotype C (adr-serotype) isolates closely related with C1 (Cs) subgenotype references from South East Asia, and three genotype A (adw2-serotype) isolates, related to Asia-variant references of subgenotype A1 (Aa). Whereas, five genotype D (ayw2, ayw3 serotype) isolates were highly divergent; one was related to subgenotype D1, two to subgenotype D3, and the remaining two clustered with a single genotype D isolate from Japan belonging to an unclassified subgenotype. Together, these two isolates differed from HBV D1-D4 subgenotypes by nucleotide differences ranging from 5.0 to 5.49%, probably indicating a new subgenotype, which we designate as D5. All serotype ayw3 of genotype D isolates had specific amino acid substitution Threonine at codon 118 and Methionine at codon 125 in antigenic determinant of surface gene that has not been reported previously in isolates from other parts of India. In conclusion; using the complete genome analyses this study has confirmed circulation of the genotype C in Eastern part of India and demonstrated considerable genotypic heterogeneity of the Indian genotype D.