Rift Valley fever (RVF) is a viral disease that can cause mild to severe symptoms. The mild symptoms may include: fever, muscle pains, and headaches which often last for up to a week. The severe symptoms may include: loss of sight beginning three weeks after the infection, infections of the brain causing severe headaches and confusion, and bleeding together with liver problems which may occur within the first few days. Those who have bleeding have a chance of death as high as 50%. The disease is caused by the RVF virus, which is of the Phlebovirus type. It is spread by either touching infected animal blood, breathing in the air around an infected animal being butchered, drinking raw milk from an infected animal, or the bite of infected mosquitoes. Animals such as cows, sheep, goats, and camels may be affected. In these animals it is spread mostly by mosquitoes. It does not appear that one person can infect another person. The disease is diagnosed by finding antibodies against the virus or the virus itself in the blood.

Prevention of the disease in humans is by vaccinating animals against the disease. This must be done before an outbreak occurs because if it is done during an outbreak it may worsen the situation. Stopping the movement of animals during an outbreak may also be useful. As may decreasing mosquito numbers and avoiding their bites. There is a human vaccine; however, as of 2010 it is not widely available. There is no specific treatment and medical efforts are supportive. Outbreaks of the disease have only occurred in Africa and Arabia. Outbreaks usually occur during periods of increased rain which increase the number of mosquitoes. The disease was first reported among livestock in Rift Valley of Kenya in the early 1900s, and the virus was first isolated in 1931. In humans, the virus can cause several syndromes. Usually, sufferers have either no symptoms or only a mild illness with fever, headache, muscle pains, and liver abnormalities. In a small percentage of cases (< 2%), the illness can progress to hemorrhagic fever syndrome, meningoencephalitis (inflammation of the brain and tissues lining the brain), or affect the eye. Patients who become ill usually experience fever, generalised weakness, back pain, dizziness, and weight loss at the onset of the illness. Typically, people recover within two to seven days after onset. About 1% of people with the disease die of it. In livestock, the fatality level is significantly higher. Pregnant livestock infected with RVF abort virtually 100% of foetuses. An epizootic (animal disease epidemic) of RVF is usually first indicated by a wave of unexplained abortions. Other signs in livestock include vomiting and diarrhoea, respiratory disease, fever, lethargy, anorexia and sudden death in young animals. The virus belongs to the Bunyaviridae family. This is a family of enveloped negative single stranded RNA viruses. All Bunyaviruses have an outer lipid envelope with two glycoproteins—G(N) and G(C)—required for cell entry. They deliver their genome into the host-cell cytoplasm by fusing their envelope with an endosomal membrane.. The virus' G(C) protein has a class II membrane fusion protein architecture similar to that found in flaviviruses and alphaviruses. This structural similarity suggests that there may be a common origin for these viral families. RVF outbreaks occur across sub-Saharan Africa, with outbreaks occurring elsewhere infrequently. In Egypt in 1977–78, an estimated 200,000 people were infected and there were at least 594 deaths.In Kenya in 1998, the virus killed over 400 Kenyans. In September 2000, an outbreak was confirmed in Saudi Arabia and Yemen. On 19 October 2011, a case of Rift Valley fever contracted in Zimbabwe was reported in a Caucasian female traveler who returned to France after a 26-day stay in Marondera, Mashonaland East Province during July and August, 2011 but later classified as not confirmed. 2006/07 outbreak in Kenya and Somalia In November 2006, a Rift Valley fever outbreak occurred in Kenya. The victims are from the North Eastern Province and Coast Province of Kenya, which had received heavy rain in recent months, causing floods and creating breeding grounds for mosquitoes, which spread the virus of the fever from infected livestock to humans.

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