Yellow fever is spread by mosquitoes infected with the yellow fever virus. Jaundice, or yellowing of the skin and eyes, is the hallmark of the infection and gives it its name. Most cases of yellow fever are mild and require only three or four days to recover, but severe cases can cause bleeding, heart problems, liver or kidney failure, brain dysfunction or death.
People with the disease can ease their symptoms, but there is no specific treatment, so prevention via the yellow fever vaccine is key. The vaccine provides immunity from the disease for 10 years or more and is generally safe for everyone older than nine months.
Yellow fever occurs only in Africa, South America and some areas of the Caribbean, so only travelers who are destined for these regions need to be concerned about it. WHO estimates that there are 200,000 cases of yellow fever every year, and 30,000 of them are fatal. The elderly are at highest risk of developing the most severe symptoms. Although vaccination and mosquito-eradication efforts have made a great difference, WHO says yellow fever cases are on the rise again.