Evolution and Epidemiology of Chikungunya Virus.

Chikungunya is a mosquito-borne Alphavirus that is spreading worldwide in the tropical areas and that has a 11.8 kb RNA genome. The most relevant vectors belong to the genus Aedes and contribute to the diffusion of the three different genotypes of the virus from the original site of first identification in East Africa. Recently, an additional site of origin has been identified in Asia. The epidemiology of Chikungunya has been extensively evaluated from 2004 when the virus initiated its travel eastbound from the coast of Africa to the Indian Ocean. It is noteworthy that this diffusion has been mainly sustained by Ae. albopictus, a new vector to which the virus become adapted due to the mutation E1-Ala226Val. This mutation was also identified during the first, even small, outbreaks of Chikungunya-related disease outside the tropics that occurred in Northern Italy in 2007 and in Southern France in 2010. Three years later the virus appeared for the first time in the Western hemisphere and since then, in less than 24 months spread to North and South America.