The Transmission Route and Selection Pressure in HCV Subtype 3a and 3b Chinese Infections: Evolutionary Kinetics and Selective Force Analysis.

Hepatitis C virus (HCV) genotype 3 (GT-3) represents 22-30% of all infections and is the second most common genotype among all HCV genotypes. It has two main subtypes, GT-3a and GT-3b, that present epidemiological differences in transmission groups. This report generated 56 GT-3a and 64 GT-3b whole-genome sequences to conduct an evolutionary kinetics and selective force analysis with reference sequences from various countries. Evolutionary analysis showed that HCV GT-3a worldwide might have been transmitted from the Indian subcontinent to South Asia, Europe, North America and then become endemic in China. In China, GT-3a may have been transmitted by intravenous drug users (IDUs) and become endemic in the general population, while GT-3b may have originated from IDUs and then underwent mutual transmission between blood donors (BDs) and IDUs, ultimately becoming independently endemic in IDUs. Furthermore, the spread of GT-3a and GT-3b sequences from BD and IDU populations exhibit different selective pressures: the proportion of positively selected sites (PPSs) in E1 and E2 from IDUs was higher than in BDs. The number of positive selection sites was higher in GT-3b and IDUs. These results indicate that different selective constraints act along with the GT-3a and GT-3b genomes from IDUs and BDs. In addition, GT-3a and GT-3b have different transmission routes in China, which allows us to formulate specific HCV prevention and control strategies in China.