Yellow fever is caused by a virus that is found mainly in rural areas of Africa and South America.
Often, yellow fever occurs without symptoms, but when symptoms do occur they may include fever attacks, shivering, extreme fatigue, headaches, back aches, and vomiting. The onset is sudden and is sometimes followed, 2 to 5 days later, by a remission lasting 12 to 24 hours. Later, renal impairment and hemorrhage may occur and the patient may gradually develop jaundice. The disease has a 20 to 30 percent mortality rate.
Yellow fever is transmitted by the bite of an Aedes mosquito, which may bite at any time during the day, mostly in shady areas or inside dwellings. It is also found in forest areas where monkeys act as reservoirs for the virus. The disease is not transmitted with every mosquito bite. The incubation period varies from 3 to 6 days. The infection confers permanent immunity.
The usual precautions against mosquitoes should be followed: apply an insect repellent, use bed netting, and wear light-coloured long-sleeve shirts and long pants. Fortunately, the risk of getting yellow fever during a trip is relatively low since international sanitary measures efficiently block its propagation.
Anyone who plans to travel to an endemic area should be vaccinated against yellow fever. The vaccine is very effective and confers sustained protection. Travellers 9 months and older can be vaccinated. It is administered in a single shot. In general, this vaccine is not associated with adverse effects, however about 10 percent of people experience weakness, stomach upset, and headaches 5 to 10 days after the shot. Many countries require travellers to be vaccinated against this disease before entering in an effort to prevent its introduction in their territory. The vaccine that is used must be approved by WHO and the traveller must go to an approved travel clinic to receive it.
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