Cache Valley virus: experimental infection in Culiseta inornata

Abstract

The dynamics of Cache Valley virus were examined in C. inornata, the probable chief vector of the virus. Of about 1500 laboratory reared C. inornata exposed to viremic suckling mice, 72 took a blood meal. A relatively high percentage (93%) of the latter mosquitoes became infected. The virus increased more than 100-fold in the experimentally infected mosquitoes. The increasing viral titers were noticed after 7 and 15 days. Peak titers averaged 105.0 SMIC(suckling mouse intracerebral)LD50/0.02 ml. Infected mosquitoes had peak titers until at least 35 days after the mosquitoes ingested blood from infected suckling mice. A single transmission of virus by bite occurred 30 days after the viremic blood meal. Transovarial transmission was demonstrated. In 2 experiments 3.3 and 2.9% of infected mosquitoes transovarially transmitted Cache Valley virus to male and female progeny. The minimum infection rate for the progeny was 2.05/1000 mosquitoes. This is the first reported experimental demonstration of transovarian transmission in a species of mosquito which overwinters as an adult. The role of transovarian transmission in the natural maintenance of Cache Valley virus remains undetermined.