|Description:||From the “Illustrated Manual for the Recognition and Diagnosis of Certain Animal Diseases”, published in 1982, by the Mexico-United States Commission for the Prevention of Foot and Mouth Disease, this photograph depicted encrustations on the muzzle and around the nares of an ovine ill with Rift Valley fever (RVF).|
“RVF, or enzootic hepatitis, is an acute arthropod-borne viral disease of sheep, cattle and goats, causing high mortality in young lambs, calves, and kids, as well as abortion in pregnant female ruminants”. RFV can simultaneously cause disease in a large number of domestic animals, which is referred to as an "epizootic". The presence of an RVF epizootic can lead to an epidemic among humans who are exposed to diseased animals. The virus is a member of the family, Bunyaviridae, and the genus, Phlebovirus.
An epizootic of RVF is generally observed during years in which unusually heavy rainfall and localized flooding occur. The excessive rainfall allows mosquito eggs, usually of the genus Aedes, to hatch. The mosquito eggs are naturally infected with the RVF virus, and the resulting mosquitoes, transfer the virus to the livestock on which they feed. Once the livestock is infected, other species of mosquitoes can become infected from the animals and can spread the disease. In addition, it is possible that the virus can be transmitted by other biting insects.