The Koutango virus Dak An D 5443 isolated from rodents of the genus Tatera belongs to the genus Flavivirus of the faily Togaviridae. This virus is very similar to the yellowfever, virus. It is experimentally transmitted from young Mouse to young Mouse by Aedes aegypti. The following observations show on one hand that this virus is found in the eggs of infected A. aegypti and on the other that the females from these eggs transmit the virus to the young Mouse by biting them.