Laboratory transmission of Wisconsin isolates of a Cache Valley-like virus by mosquitoes.

Abstract

Two Wisconsin isolates, W-523 and W-993, of a Cache Valley-like virus were infective to mosquitoes when mixed with normal defibrinated guinea pig blood and ingested through a membrane. Only W-993, however, was transmitted to suckling mice. Both infection and transmission rates varied with mosquito species and the number of mouse brain passages of the ingested virus. Infectivity of W-523-P4 (passage number 4) was high (100%) for Anopheles qiiadrimaculatus when a dosage of 104.8 ICLD50/0.03 ml of blood and moderate for Aedes vexans (43%) and Aedes sticticus (40%) at dosages of 105.5 and 104.8 ICLD50/0.03 ml, respectively. Infectivity of the 10th passage of this virus was much lower. W-993, at low passages, was transmitted by A. quadrimaculatus, Anopheles punctipennis A. vexans. A. quadrimaculatus showed the greatest transmission efficiency, averaging 47% and 37%, respectively, when the mosquitoes ingested a W-993-P4 dosage of 105.5 or 105.6 ICLD60/0.03 ml. Transmission efficiency was much lower with the 7th and subsequent passages. W-993, 4th passage, exhibited a normal replication pattern in A. quadrimaculatus while high passages failed to multiply in the mosquitoes. Aedes vexans was a less efficient transmitter than either Anopheles species. The latter appeared capable of being biological vectors of Cache Valley virus in nature.