Background. The analysis of molecular phylogenies estimated from the gene sequences of sampled viruses can provide important insights into epidemiological processes. Methods. The demographic and migration histories of the prevalent hepatitis C virus (HCV) subtypes 1a and 1b were inferred from viral gene sequences sampled in 5 countries. Estimated viral phylogenies were analyzed by use of methods based on parsimony and coalescent theory. Results. The parsimony migration analysis suggested that the global subtype 1a and 1b epidemics are geographically structured, with asymmetrical movement of HCV strains among the sampled countries. The coalescent analysis indicated that subtype 1a infections in the United States, Brazil, and Indonesia began to increase exponentially during the 1940s and 1950s, whereas in Vietnam the increase began after the 1970s. In contrast, subtype 1b infections in these 4 countries and in Japan began to increase exponentially between 1880 and 1920, with a possible recent decrease in infection rates in Indonesia and Japan. In the United States, Brazil, and Vietnam, the epidemic growth rates for subtype 1a strains were higher than those for subtype 1b strains, whereas the growth rates were similar in Indonesia. Conclusions. The estimated histories of migration and population growth indicated that patterns of HCV transmission differ among countries and viral subtypes.
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