Effect of extrinsic incubation temperature on the ability of Aedes taeniorhynchus and Culex pipiens to transmit Rift Valley fever virus.

Studies were conducted to examine the effects of extrinsic incubation (EI) temperature on the vector competence of Egyptian Culex pipiens and North American Aedes taeniorhynchus for Rift Valley fever (RVF) virus. Following per os exposure, infection rates in Ae. taeniorhynchus remained relatively constant at 55%, 56%, and 59% for mosquitoes held at EI temperatures of 13, 26, and 33 degrees C, respectively. In contrast, significantly fewer Cx. pipiens became infected when held at 13 degrees C (38%), than when held at 26 degrees C (75%) or 33 degrees C (91%). In both species, viral dissemination and transmission occurred earlier in mosquitoes held at high temperatures as compared to those held at low temperatures. Following EI at 26 or 33 degrees C, Cx. pipiens were able to transmit virus as early as 1 day after inoculation with RVF virus. However, 3 days were required before the first transmissions by inoculated Ae. taeniorhynchus. Temperature of EI affected these 2 species differently in their ability to transmit RVF virus. Because of the importance of EI temperature on infection and transmission rates, as well the length of the EI period, the role of EI temperature will need to be evaluated for each virus and vector pair.