Overview
Yellow fever is an infectious disease caused by the yellow fever virus. It is mainly found in tropical areas of Africa and South America where certain mosquitoes carry the virus. Many people recover after a mild illness, but some develop a dangerous second phase with jaundice, bleeding, shock, or organ failure.
Key Symptoms
Early symptoms often begin suddenly and may include fever, chills, severe headache, back pain, muscle aches, nausea, vomiting, loss of appetite, and weakness. Some people improve after a few days, but others become sick again with more serious problems. Warning signs include yellowing of the skin or eyes, stomach pain, vomiting blood, bleeding from the nose or gums, dark urine, confusion, or reduced urination.
Causes and Risk Factors
Yellow fever is caused by a virus transmitted through the bite of an infected mosquito. Risk is higher for people who live in, work in, or travel to areas where yellow fever is present, especially if they are not vaccinated. Mosquito exposure is more likely in forests, rural areas, and places without strong mosquito control or protective measures.
Who Is Affected
Anyone who is bitten by an infected mosquito can get yellow fever. People traveling to endemic regions may be at risk if they are not vaccinated or do not use mosquito protection. Severe illness can happen in adults and children, and the risk of serious outcomes may be higher in some older adults and in people with certain health conditions.
Prevention
Vaccination is a key preventive step for people living in or traveling to affected regions, based on local public health guidance and travel requirements. Avoiding mosquito bites also matters: use insect repellent, wear long sleeves and pants, stay in screened or air-conditioned spaces, and use bed nets when needed. Reducing mosquito breeding sites around homes, such as standing water, can also help.
Diagnosis and Tests
A healthcare professional may suspect yellow fever based on symptoms, travel history, vaccination history, and possible mosquito exposure. Blood tests are used to help confirm the infection and check for liver, kidney, and bleeding problems. Other illnesses with similar symptoms, such as malaria, dengue, viral hepatitis, or other infections, may also need to be considered.
Treatment Categories
There is no specific antiviral treatment for yellow fever. Medical care focuses on supporting the body, such as fluids, monitoring, oxygen if needed, and treatment of complications like dehydration, bleeding, or organ problems. People with severe illness may need hospital care, sometimes in an intensive care setting.
When to Seek Medical Care
Seek medical care promptly if you develop fever or flu-like symptoms after travel to an area where yellow fever occurs, or after many mosquito bites in a risk area. Tell the healthcare professional where you traveled and whether you had a yellow fever vaccine. Early evaluation is important because several serious tropical infections can start with similar symptoms.
When It May Be an Emergency
Get emergency medical help right away for trouble breathing, confusion, seizures, fainting, severe weakness, persistent vomiting, signs of dehydration, yellowing of the eyes or skin, vomiting blood, black stools, unusual bleeding, or very little urine. These symptoms can signal severe yellow fever or another medical emergency.