Yellow fever

An infectious disease of short duration and variable severity that is caused by a virus transmitted by mosquitoes. In severe cases, the skin yellows due to jaundice, from which the name yellow fever derives. The infection may be spread from monkeys to humans in forest areas through various species of mosquito; and in urban areas it can be transmitted between humans by mosquitoes. Today, yellow fever is contracted only in Central America, parts of South America, and a large area of Africa. Eradication of the causative mosquito from populated areas has greatly reduced its incidence. Yellow fever is characterised by a sudden onset of fever and headache, often with nausea and nosebleeds and, despite the high fever, a very low heart-rate. In more serious cases, the fever is higher and there is severe headache and pain in the neck, back, and legs. Damage may occur rapidly to the liver and kidneys, causing jaundice and kidney failure. This may be followed by severe agitation and delirium, leading to coma and death. Vaccination confers long-lasting immunity and should always be obtained before travel to affected areas. A single injection of the vaccine gives protection for at least 10 years. Reactions to the vaccine are rare and are usually trivial, although children under the age of 1 should not be vaccinated. During yellow fever epidemics, diagnosis is simple. A diagnosis can be confirmed by carrying out blood tests to isolate the causative virus or to find antibodies to the virus. No drug is effective against the yellow fever virus; treatment is directed at maintaining the blood volume. Transfusion of fluids is often necessary. Many patients recover in about 3 days and, in mild to moderate cases, complications are few. Relapses do not occur and one attack confers lifelong immunity. Overall, however, about 10 per cent of victims die.