Yellow Fever

Yellow fever is an infectious disease caused by a virus that is transmitted to humans by mosquitoes.

What Is Yellow Fever?

Yellow fever is a disease caused by yellow fever virus, a member of the flavivirus (FLAY-vih-vy-rus) group of viruses. The disease gets its name because it often causes jaundice*, which tints the skin yellow, and a high fever. Yellow fever also can cause kidney failure and uncontrolled bleeding, or hemorrhaging (HEM-rij-ing). Many cases produce only mild illness, but severe cases of yellow fever can be fatal. Once someone has survived the disease, the person has lifetime immunity against it.

Yellow fever afflicts both humans and monkeys and has been known since at least the 1600s. The disease is not spread by person-to-person contact. It is transmitted by several different species of mosquitoes; a person can contract yellow fever only from the bite of a mosquito that has bitten an infected person or monkey.

The disease once caused epidemics in the Americas, Europe, and the Caribbean, but at the beginning of the 21st century the disease occurred almost exclusively in South America and Africa. Each year, outbreaks lead to an estimated 200,000 cases and 30,000 deaths worldwide. Vaccines against the virus were developed in 1928 and 1937, and mosquito-eradication programs made great progress in controlling the disease. The last recorded outbreak of yellow fever in the United States was in New Orleans in 1905. However, lapses in prevention programs in Africa and South America allowed yellow fever to once again become a serious public health issue on those continents.

Are There Different Kinds of Yellow Fever?

Yellow fever occurs as three subtypes: epidemic (urban), intermediate, and jungle-acquired. Epidemic yellow fever spreads in densely populated areas of Africa and South America via the bite of Aedes aegypti (a-E-deez eh-JIP-tie) mosquitoes. Intermediate yellow fever occurs in Africa as the result of mosquitoes breeding in humid flat grasslands (savannahs) during rainy seasons, then infecting both monkeys and humans. In dry seasons, the virus can remain alive in unhatched mosquito eggs that are resistant to the heat.

Jungle-acquired yellow fever occurs mainly in South America when mosquitoes pick up the virus from infected forest monkeys and then transmit the disease to humans in jungles and rainforests. People who are regional settlers, soldiers, or agricultural or forestry workers are at greater risk for this less common form of the disease.