Yellow fever is caused by infection with yellow fever virus, which is transmitted by the bite of infected mosquitoes. It occurs in tropical regions of Africa and in parts of South America.

Yellow fever can be prevented by vaccination. Travelers should get vaccinated for yellow fever before visiting areas where yellow fever occurs. In the United States, the vaccine is given only at designated yellow fever vaccination centers. International regulations require proof of yellow fever vaccination for travel to and from certain countries. People who get vaccinated should be given an International Certificate of Vaccination.

Mosquitoes that spread yellow fever usually bite during the day, especially at dusk and dawn. Travelers should take precautions against mosquito bites when in areas with yellow fever transmission.

There are two kinds of yellow fever, spread by two different cycles of infection:

Jungle yellow fever is mainly a disease of monkeys. It is spread from infected mosquitoes to monkeys in the tropical rain forest. People get jungle yellow fever when they are bitten by mosquitoes that have been infected after feeding on infected monkeys. Jungle yellow fever is rare and occurs mainly in persons who live or work in tropical rain forests.

Urban yellow fever is a disease of humans. It is spread by mosquitoes that have been infected by other people. Aedes aegypti is the type of mosquito that usually carries yellow fever from human to human. These mosquitoes have adapted to living among humans in cities, towns, and villages. Their larvae grow in discarded tires, flower pots, oil drums, and water storage containers close to human dwellings. Urban yellow fever is the cause of most yellow fever outbreaks and epidemics.

Illness ranges in severity from a self-limited febrile illness to severe hepatitis and hemorrhagic fever. Many yellow fever infections are mild, but the disease can cause severe, life-threatening illness. Symptoms of severe infection are high fever, chills, headache, muscle aches, vomiting, and backache. After a brief recovery period, the infection can lead to shock, bleeding, and kidney and liver failure. Liver failure causes jaundice (yellowing of the skin and the whites of the eyes), which gives yellow fever its name. Severe yellow fever infections can be fatal. Case-fatality rates from severe disease range from 15% to more than 50%.

There is no specific treatment for yellow fever. Treatment is symptomatic-rest, fluids, and ibuprofen, naproxen, acetaminophen, or paracetamol may relieve symptoms of fever and aching. Infected persons should be protected from further mosquito exposure (staying indoors and/or under a mosquito net during the first few days of illness) so that they can’t contribute to the transmission cycle.

The geographic range of the virus is South America and Africa. For information on current outbreaks, consult CDC’s Travelers’ Health website. Given the current yellow fever epidemics and the world wide distribution of Aedes aegypti, there is a risk of importation of yellow fever into new areas by infected travelers.

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