Circulation of genotype-I hepatitis B virus in the primitive tribes of Arunachal Pradesh in early sixties and molecular evolution of genotype-I

•High HBV endemicity in the Indian primitive tribe for 5 decades.•Circulation of HBV-genotype-I in this tribe since at least 1963.•HBV-I in 1963 and 2005 showed identical recombinant breakpoints revealing stability.•Molecular clock analysis predicted existence of genotype-I in this tribe during 1920s.•Analyses demonstrated that recombination events were not recent.

Retrospective serologic screening of 1077 serum samples collected from the primitive tribe from north-eastern India in 1963 revealed high prevalence of HBV (15% HBsAg carrier rate) and HCV (7% anti-HCV positivity) and co-circulation of multiple HBV genotypes-A, C, D and G. Full genome sequencing classified all the G-genotype samples as genotype-I. Comparison of genotype-I-HBV full-genome sequences representing 1963 (n = 5, this study) and 2005 (reported earlier) showed identical recombination break-points of genotypes-A/G/C. Genotype-C and genotype-C-fragment of I-genotype circulating in 1963 were distinctly different. The data demonstrates that the recombination events were not recent. Molecular clock analysis predicted existence of genotype-I in this tribe during 1920s.