Yellow fever is a disease caused by a virus passed on through the bite of a daytime-biting mosquito. Yellow fever happens only in certain areas of Africa, Central America, and South America. The disease causes flu-like symptoms, slow and weak pulse, bleeding of the gums, bloody urine, and yellow skin (jaundice). Treatment is aimed at controlling the symptoms. It includes rest and plenty of fluids. You may also need to take medicine to help relieve fever and aching. A vaccine is available to prevent yellow fever. You may need it before traveling to some tropical countries in Africa, Central America, or South America.