Chikungunya is a mosquito-borne alpha virus that was first isolated after a 1952 outbreak in modern-day Tanzania. The virus has circulated in forested regions of sub-Saharan African in cycles involving nonhuman primate hosts and arboreal mosquito vectors. Phylogenetic studies indicate that the urban transmission cycle—the transmission of a pathogen between humans and mosquitoes that exist in urban environments—was established on multiple occasions from strains occurring on the eastern half of Africa in non-human primate hosts. This emergence and spread beyond Africa may have started as early as the 18th century. Currently, available data does not indicate whether the introduction of chikungunya into Asia occurred in the 19th century or more recently, but this epidemic Asian strain causes o