Causes of yellow fever

The virus circulates between mosquitoes and susceptible people in areas where transmission occurs. A mosquito becomes infected after feeding on an infected host and can pass the virus during a later bite. Early illness may include fever, headache, muscle aches, nausea, vomiting, or marked tiredness. Some people develop a more serious illness affecting the liver and other organs, which can cause jaundice, bleeding, confusion, or reduced urine. Travel history matters because exposure risk depends on the destination, season, mosquito activity, and local transmission.

Before travel to an area where yellow fever may occur, ask a travel-health clinician whether vaccination is suitable and whether an official certificate is needed for your journey. Reduce mosquito bites with long clothing, insect repellent, screens, and air-conditioned or screened accommodation where possible. If fever develops during travel or after returning, mention every recent destination and seek medical advice promptly.

Seek urgent medical care for fever after travel to a risk area, especially with yellow eyes or skin, repeated vomiting, bleeding, confusion, severe weakness, or worsening drowsiness. Do not wait for symptoms to become severe before explaining the travel exposure.

Ask whether your destination carries risk, whether yellow fever vaccination is appropriate for you, how to protect yourself from mosquito bites, and what symptoms after travel need urgent review.