Rift Valley fever
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Rift Valley fever,acute viral disease that affects domestic livestock and can be transmitted to humans. The disease is most common in E and S Africa, but also occurs widely in sub-Saharan Africa and in parts of the Arabian Peninsula. In animals the disease is typically transmitted by the Aedes and sometimes other mosquitoes and by blood-feeding flies; humans typically acquire it by direct or indirect exposure to the blood or organs of infected animals, but insect transmission also occurs.
Rift Valley fever can cause severe disease in sheep, goats, cattle, buffalo, and camels. The most devastating outbreaks typically occur among sheep and goats, killing up to 90% of young animals and causing pregnant females to miscarry; it is less deadly to adult animals. Outbreaks can have severe economic consequences as a result of herd losses, but the disease can be prevented through vaccination.
In humans, the disease is usually mild. After an incubation period of 2 to 6 days, most persons experience no or just flulike symptoms (fever, muscle and joint pain, headache). In some cases, meningitislike symptoms including a stiff neck, sensitivity to light, poor appetite, and vomiting may occur. Symptoms may last for up to a week. In rare instances (less than 4% of human infections), however, more severe forms of the disease occur. In some cases, lesions that affect the vision can develop in the retina up to three weeks after symptoms begin, and in about half of these cases lesions in the macula result in permanent vision loss, including blindness in one or both eyes. In other cases, encephalitis may develop, usually within four weeks of the first symptoms, producing extreme headache, hallucinations, confusion, convulsions, and sometimes coma; death sometimes results. Recovery can be slow, and there can be long-term neurological complications. In the most severe human cases, hemorrhagic fever develops within the first week of symptoms. Jaundice and other signs of severe liver impairment are followed by symptoms of hemorrhaging including bleeding from the nose and gums and from injection sites, with death occurring in about half these cases.
Medical treatment in all cases is supportive care; there is no drug therapy, and vaccination has only been available experimentally for persons at high risk for acquiring the disease. Prevention of human cases primarily focuses on preventing the disease in livestock through vaccination, controlling insects that transmit the disease, and exercising appropriate care and caution when dealing with potentially infected livestock or their carcasses or tissues.
Rift Valley fever
An arthropod-borne (primarily mosquito), acute, febrile, viral disease of humans and numerous species of animals. Rift Valley fever is caused by a ribonucleic acid (RNA) virus in the genus Phlebovirus of the family Bunyaviridae. In sheep and cattle, it is also known as infectious enzootic hepatitis. First described in the Rift Valley of Africa, the disease presently occurs in west, east, and south Africa and has extended as far north as Egypt. Historically, outbreaks of Rift Valley fever have occurred at 10–15-year intervals in normally dry areas of Africa subsequent to a period of heavy rainfall.
In humans, clinical signs of Rift Valley fever are influenzalike, and include fever, headache, muscular pain, weakness, nausea, epigastric pain, and photophobia. Most people recover within 4–7 days, but some individuals may have impaired vision or blindness in one or both eyes; a small percentage of infected individuals develop a hemorrhagic syndrome and die.
Rift Valley fever should be suspected when high abortion rates, high mortality, or extensive liver lesions occur in newborn animals. The diagnosis is confirmed by isolating the virus from tissues of the infected animal or human. Control of the disease is best accomplished by widespread vaccination of susceptible animals to prevent amplification of the virus and, thus, infection of vectors. Any individual that works with infected animals or live virus in a laboratory should be vaccinated. See Animal virus, Vaccination