Birds and mosquitoes. Human outbreaks after rains. Rift Valley Fever . East Africa, Egypt, Israel, South Africa. Definitive host not identified.
Human outbreak follows animal outbreak after rains.
SE Asia,, Carribean and Central America. 4 Serological strains without cross-protection. Previous exposure may predispose to haemorrhagic form. Almost all arboviruses may infect the CNS but some characteristically produce an encephalitis in man. Symptoms start with fever, progressively severe headache, nausea and vomifing, neck stiffness, paralysis, decreased consciousness, convulsions and death in severe cases.