Yellow fever is a mosquito-borne viral disease that occurs in tropical areas. It is transmitted by the Aedes aegypti mosquito and has two main types: urban yellow fever spreads among humans in cities, while sylvatic yellow fever circulates between monkeys and humans in jungles. Symptoms appear within three to six days and include fever, headache, and bleeding from the eyes, nose or mouth. There is no cure for yellow fever, but vaccination provides lifelong immunity for those traveling to affected areas.