Molecular evolution of Crimean-Congo hemorrhagic fever virus based on complete genomes.

Crimean-Congo hemorrhagic fever virus (CCHFV), which is widely distributed in parts of Asia, Africa and Europe, often causes fatal viral infections in humans. However, its evolutionary features are still unclear. In this study, a total of 22 global CCHFV strains with complete genome segments were analysed. Three medium (M) segment reassortants and two small (S) segment reassortants were newly identified. According to Bayesian analysis of the S, M and large (L) segment datasets with and without reassortants, inclusion of reassortants was approved to bias Bayesian analysis of the S and L segments, but not the M segment. The mucin domain of the M segment had no effect on evolutionary rate estimates, but had slight effects on the time to the most recent common ancestor. Selection pressure analysis suggested that CCHFV was under strong purifying selection regardless of the S, M and L segments, and that the L segment was also shaped by positive selection. Bayesian analysis in this study indicated the evolutionary features of CCHFV, which were helpful in investigating the molecular evolution, CCHF surveillance and the pathogenicity of CCHFV and other viruses in the family Bunyaviridae.