Yellow fever virus was isolated from Aëdes simpsoni caught in 1942 in a forestedge plantation in Western Uganda 11 months after the effective mass immunization of the human population.
The virus was again isolated in 1944 from a lot of 80 Aëdes mosquitoes, including 12 different species but not including A. aegypti or A. simpsoni. These mosquitoes were taken in the uninhabited Semliki Forest, indicating an extrahuman cycle of virus activity involving a forest vector.
The implications of the results are discussed with reference to the epidemiology of the disease in forest regions and the means by which the infection reaches man.
Staff members of the International Health Division, Rockefeller Foundation.
This Institute is supported jointly by the Medical Department of the Uganda Protectorate and the International Health Division of The Rockefeller Foundation.