Rift Valley fever (RVF) is an acute disease of domestic ruminants in mainland Africa and Madagascar, caused by a mosquito borne virus and characterized by necrotic hepatitis and a haemorrhagic state. Large outbreaks of the disease in sheep, cattle and goats occur at irregular intervals of several years when exceptionally heavy rains favour the breeding of the mosquito vectors, and are distinguished by heavy mortality among newborn animals and abortion in pregnant animals. Humans become infected from contact with tissues of infected animals or from mosquito bite, and usually develop mild to moderately severe febrile illness, but severe complications, which occur in a small proportion of patients, include ocular sequelae, encephalitis and fatal haemorrhagic disease. Despite the occurrence of low case fatality rates, substantial numbers of humans may succumb to the disease during large outbreaks. Modified live and inactivated vaccines are available for use in livestock, and an inactivated vaccine was used on a limited scale in humans with occupational exposure to infection. The literature on the disease has been the subject of several extensive reviews from which the information presented here is drawn, except where indicated otherwise (Henning 1956; Weiss 1957; Easterday 1965; Peters and Meegan 1981; Shimshony and Barzilai 1983; Meegan and Bailey 1989; Swanepoel and Coetzer 2004; Flick and Bouloy 2005). In September 2000, the disease appeared in south-west Saudi Arabia and adjacent Yemen, and the outbreak lasted until early 2001 (Al Hazmi et al. 2003; Madani et al. 2003; Abdo-Salem et al. 2006). The virus was probably introduced with infected livestock from the Horn of Africa, and it remains to be determined whether it has become endemic on the Arabian Peninsula.
Rift Valley fever in the Horn of Africa: challenges and opportunities