Abstract
While Davis, Frobisher and Lloyd 1 failed to find evidence of multiplication of yellow fever virus in infected Aëdes aegypti, the experiments of St. John, Simmons and Reynolds 2 and of Holt and Kintner, 3 though limited in number, suggest that the dengue fever virus does multiply in its transmitting insect host. We have reported 4 that Aëdes sollicitans fed on animals infected with the eastern strain of equine encephalomyelitis virus show, by titration of the suspension of a given number of insects, a greater concentration of virus at 5 days than immediately after feeding. Titration experiments are not absolutely convincing and we therefore adopted a modification of the method used by St. John, Simmons and Reynolds in order to determine whether the equine encephalomyelitis virus could be carried by serial passage through mosquitoes. If it can be carried from mosquito to mosquito directly the proof of the multiplication of the virus is convincing.
Thirty female Aëdes aegypti infected 5 days previously by feeding on brain virus of the western strain of equine encephalomyelitis were suspended in 4 cc. salt solution plus 1 cc. normal horse serum. An equal amount of defibrinated horse blood was added and a pledget of cotton in a Petri dish was moistened with the mixture. A small amount of sugar was sprinkled over the surface of the cotton and the Petri dish was placed in a cage containing female Aëdes aegypti that had had no sugar solution for 4 days and no water for one day. Since the virus deteriorates rapidly when in contact with the air at room temperature, the Petri dish was replaced in an hour's time by one containing the mixture that had been kept in the refrigerator.
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