Countries in which autochthonous cases of CHIKV have been reported are specified with colored symbols representing the distinct viral genotypes detected during outbreaks in that country. West African strains are indicated by purple triangles; Asian strains are indicated by green circles; East/South/Central African (ESCA) strains are indicated with blue squares; strains of the Indian Ocean lineage, a subtype of the ESCA clade, are indicated with blue squares with a cross; and strains whose genotype has not been determined are indicated with gray diamonds. Symbols are shaded to differentiate transmission prior to (darker hue) or after (lighter hue) the reemergence of the virus in the Indian Ocean (ECSA strain in 2005) and Pacific Islands (Asian strain in 2010). Symbols indicate the countries in which natural transmission has occurred and are not meant to indicate precise locations of outbreaks. Overlayed with CHIKV distribution is the geographic range of the two primary vectors responsible for urban mosquito-human-mosquito transmission of the virus. Range of Ae. aegypti is indicated in red; range of Ae. albopictus is indicated in yellow; and areas where both mosquito species are present are indicated in orange. Endemic CHIKV data were obtained from numerous PubMed publications (1, 3, 23, 24, 28, 30–32, 37, 38, 46–62). Range of mosquito data was obtained from (63).