Identification of Indian sub-continent as hotspot for HCV genotype 3a origin by Bayesian evolutionary reconstruction

Recent emphasis in Hepatitis C virus (HCV) evolutionary biology has focused on analysis using Core, E1/E2 and/or NS5b regions, with limited appreciation of full length genome. While HCV genotypes have been described as endemic in the Indian subcontinent, there has been no confirmation at the molecular evolutionary level of these genotypes. We have attempted here to determine the status of Indian HCV genotype 3a sequences in relation to similar genotypes from other parts of the world.

Cloning, sequencing and molecular characterization was performed on 9 Indian sequences and comparative analyses were performed with 46 sequences from other countries. Evolutionary-rate and molecular-clock hypothesis testing was addressed by Bayesian MCMC.

Genetic analysis of full length genome revealed two hypervariable regions (HVR) in E2 region - HVR496 and HVR576, with a variable 5-8 amino-acid insertion sequence and a putative N-glycosylation site. Phylogenetic analysis revealed a divergence resulting in 2 distinct clades: clade-1 represented by HCV 3a subtype and clade-2 represented by other 3 subtype genomes. Clade-2 shows earlier divergence than clade-1. Analysis revealed that genotype 3a genomes from India roots out first (∼99 years ago) in clade1. Bayesian skyline plot analysis revealed an increase in effective number of infections from 1940s to 1990s, followed by a gradual decrease after 2000.

Genotype 3a sequences appear to have originated in India and later dispersed to United Kingdom around mid 1940s, most likely around the time of Indian independence and World War II.