Yellow fever is a disease caused by a virus. People get infected with the virus after being bitten by an infected mosquito usually in tropical areas of Africa and South America. Early symptoms may include fever, headache, vomiting, and backache. As the disease continues, symptoms may include slow/weak pulse, bleeding gums, blood in the urine, and jaundice (yellow skin and eyes). There is no specific treatment for yellow fever and most people get better on their own. Yellow fever can be prevented with a vaccine.