Yellow fever is caused by a virus that is transmitted by mosquitoes, and occurs in Africa and South America. The disease vectors in Africa are Aedes aegypti, Aedes simpsaloni and Aedes africanus. In South America, the vectors are of the Haemagogus genus. The virus is a member of the Flaviviridae family, which also includes the West Nile virus, as well as the viruses that cause dengue, hepatitis C and several other insect-borne viruses.