Studies on Aedes aegypti Infected in the Larval Stage with the Virus of Yellow Fever. ∗

Abstract

During the course of general transmission studies with Aedes aegypti, it became of interest to see whether these mosquitoes could be infected in the larval stage, and retain the infection into adult life. To this end, half-grown larvae were placed in a bowl containing a mixture of blood serum from a Rhesus monkey at the height of infection with the Asibi strain of yellow-fever virus, and an equal quantity of physiological salt solution. This was shown, by titration in mice, to contain 30,000,000 minimum lethal doses for mice per cc Pupation commenced after 48 hours. The pupae were washed and suspended individually in tubes of clean water, and the adults began to emerge 4 days after the first contact with the virus. The first 28 males to emerge were ground up and injected into a Rhesus monkey subcutaneously on the day of emergence. The monkey responded 4 days later with fever, and had virus in its blood stream. It was killed when moribund on the sixth day. Necropsy findings, both macroscopic and microscopic, were typical of yellow fever. Four days later, 15 females, varying in age from one to 4 days, were fed on a normal Rhesus, but failed to infect it. However, 10 days later 29 females from the same lot were able to produce yellow fever by bite in another Rhesus monkey.

To confirm this observation, half-grown larvae were again placed in 50% serum from an infected Rhesus, This mixture was shown to contain 7,600,000 M.L.D. for mice per cc. In order to prevent the mosquitoes from pupating in the viral suspension, the larvae were washed 3 times in water at the end of 24 hours, and placed in a bowl of clean water.