Yellow fever is a mosquito-borne viral disease that occurs mainly in the tropics.

Yellow fever is caused by a flavivirus. Mosquitoes are responsible for spreading yellow fever. Yellow fever is one of the most recognized and historically important viral infections. In the past, major epidemics of yellow fever caused tens of thousands of deaths. Once common in tropical and temperate zones around the world, the disease now occurs only in the tropical areas of Central Africa and Central and South America.

Some infected people do not have symptoms. The first symptoms are headache, muscle aches, chills, and mild fever, which begin suddenly. Nausea, vomiting, constipation, extreme fatigue, and restlessness are common. All of these symptoms subside after a few days. Some people then recover, but others develop a high fever, nausea, vomiting, and severe generalized pain a few hours or days after the initial symptoms subside. The skin turns yellow (jaundice) because the liver is infected. Often, there is bleeding from the nose, mouth, and gastrointestinal tract. People may become confused and apathetic. Some people develop very low blood pressure (shock). Severe infection can cause seizures, malfunction of several organs, and coma. Up to 10% of people with severe symptoms die.

Doctors suspect yellow fever when people living in an area where the infection is common have typical symptoms. It is diagnosed by growing (culturing) the virus or by detecting antibodies to the virus in the blood.

Avoiding mosquito bites is key to prevention. A vaccine that is 95% effective at preventing yellow fever is available. Many countries require vaccination for travelers coming into their country from areas where yellow fever occurs.

Treatment involves supportive care, including drugs to treat or prevent bleeding. There is no specific treatment for the infection.

Last full review/revision November 2009 by Marguerite A. Urban, MD