Yellow fever is a viral disease that occurs in the tropical and subtropical areas of Africa and the Americas. An infection with the yellow fever virus may lead to only mild symptoms, but can also cause a severe, life-threatening illness. The disease is normally transmitted by the mosquito Aedes aegypti. Other related mosquitoes, especially Aedes albopictus may also play a role in the transmission in certain areas.

The disease has two phases. Three to six days after the infection, a first phase occurs which is often characterized by high fever, headache, muscle pain and backache, shivers, vomiting, and other symptoms. During this phase, yellow fever is especially difficult to recognize and can easily be confused with other infectious diseases and even poisonings. After three to four days, most patients improve and their symptoms disappear.

However, 15% of them enter a second phase. Within 24 hours, the patient again develops fever, with jaundice, strong abdominal pains, vomiting, bleeding from the mouth, nose, eyes and/or stomach, and blood in the vomit and faeces. For about half of the patients, this second phase is fatal.

There is no specific treatment for yellow fever once an infection has occured. People traveling to places with yellow fever should be immunized.