Figure 2.

Experimental design. Donor Texel-Swifter lambs were infected by intravenous injection of Rift Valley fever virus (RVFV) two days prior to feeding ~1000 laboratory reared Aedes aegypti. All blood fed mosquitoes were subsequently pooled, and kept in a climate and light controlled incubator in a BSL3 laboratory. To estimate RVFV infection rates, 30 mosquitoes were tested for RVFV infection and presence of virus in saliva by RT-qPCR. Twelve days post initial feeding mosquitoes were allowed to take a second blood meal; three (low-exposure group) or 28-31 mosquitoes (high exposure group) were placed in mesh screen containers and allowed to feed on the shaven inner thigh of 10-week-old naive lambs. After mosquito exposure, the lambs were monitored 2-3 times daily for abnormalities and rectal temperatures were measured. Blood samples were taken (red drop in figure). Animals were euthanized and during necropsy liver and spleen samples were collected for detection of RVFV.