Global spread and evolutionary history of HCV subtype 3a

Studies have shown that HCV subtype 3a had likely been circulating in South Asia before its global spread. However, the time and route of this dissemination remain unclear. For the first time, we generated host and virus genome-wide data for more than 500 patients infected with HCV subtype 3a from the UK, North America, Australia and New Zealand. We used the host genomic data to infer the ancestry of the patients and used this information to investigate the epidemic history of HCV subtype 3a. We observed that viruses from hosts of South Asian ancestry clustered together near the root of the tree, irrespective of the sampling country and that they were more diverse than viruses from other host ancestries. We also inferred that three independent transmission events resulted in the spread of the virus from South Asia to the UK, North America and the Australian continent. This initial spread happened during or soon after the end of the second world war. This was followed by an exponential growth in the effective population size of HCV subtype 3a worldwide and many independent transmissions between the UK, North America and Australian continent. Using both host and virus genomic information can be highly informative in studying the virus epidemic history especially in the context of chronic infections.