Nairobi sheep disease.

Nairobi sheep disease is probably the most pathogenic virus known for sheep and goats. It is transmitted by an Ixodid tick, both trans-stadially and transovarially and causes an acute gastroenteritis. In totally susceptible populations, mortality rates of over 90% regularly occur. The infection also causes abortion. The disease is known to occur in East Africa, Somalia and Rwanda. It may exist in the south east of Ethiopia. No evidence for its existence has been found in those parts of Africa where the principle vector tick, Rhipicephalus appendiculatus has a seasonal breeding cycle. Thus countries like Zambia, Zimbabwe and Botswana appear to be free from the disease.