An acute infectious disease caused by a virus transmitted by the bite of an infected mosquito, yellow
fever may occur in a mild form similar to influenza but in its classical form is a severe illness. In severe cases, after an incubation period of three to six days, the
onset is sudden,
usually with fever, headache, backache, nausea, and vomiting. The temperature typically returns to normal around the third day, but it rises again. Mucosal bleeding causes "black vomit" and dark stools. Fatty degeneration of the liver, kidney, and heart is common.
Victims often become jaundiced, a symptom that accounts for the disease's name. There is no specific treatment. Most victims recover spontaneously and gain lifelong immunity. The mortality rate is approximately 5 to 10 percent; death usually occurs four to eight days after the onset of symptoms. Vaccination confers protection for at least ten years.
Diseased monkeys in Africa and tropical America are probably the main source of infection. Infected forest-canopy mosquitoes occasionally transmit the virus to a human who, in moving to a populated area, infects the "domestic"
mosquito and primary
vector Aedes aegypti. This vector was first demonstrated by Walter Reed, Jesse William Lazear, and coworkers in 1901, in a successful effort to
control the disease so that the Panama Canal could be built. This led to the mosquito-control measures that remain the only effective means for preventing yellow fever epidemics.
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