Rift Valley fever is a viral disease of sheep, cattle, monkeys and rodents and is transmitted to humans by vector mosquito bites. It is not contagious and occurs chiefly in Africa. The symptoms are like those of dengue fever with headache, weakness, fever and sometimes nausea and vomiting. The illness is usually brief and complete recovery is the rule. The disease causes abortions, disease and death in infected herds or flocks (mainly of cattle and sheep).