Figure 1. Intranasal inoculation results in fatal encephalitic disease.

C57BL/6 mice were inoculated with various doses of Rift Valley fever virus (RVFV) lacking the NSs gene (ΔNSs) intranasally (IN) or subcutaneously in the footpad (FP). (A) FP-inoculated mice survived with no indication of clinical signs. IN-inoculated mice developed dose-dependent disease. Survival curves were significantly different (p<0.0001). (B) All mice that succumbed to ΔNSs virus IN infection at high doses (1×10⁴ or 1×10⁵ TCID₅₀/per nare) had significantly higher viral RNA loads in the brain than in the liver, as measured by RVFV-specific qRT-PCR (p<0.0001).