Yellow fever occurs only in Africa and South America. The clinical spectrum of yellow fever ranges from subclinical infection to overwhelming pansystemic disease. Yellow fever has an abrupt onset after an incubation period of 3–6 days, and usually includes fever, prostration, headache, photophobia, lumbosacral pain, extremity pain (including the knee joints), epigastric pain, anorexia, and vomiting. The illness might progress to liver and renal failure, and hemorrhagic symptoms and signs caused by thrombocytopenia and abnormal clotting and coagulation can occur. The fatality rate of severe yellow fever is approximately 20%.
Treatment for yellow fever consists of providing general supportive care and varies, depending on which organ systems are involved. No effective specific antiviral therapy for yellow fever has been identified.
Two forms of yellow fever, urban and jungle, are epidemiologically distinguishable. Clinically and etiologically they are identical. Urban yellow fever is an epidemic viral disease of humans transmitted from infected to susceptible persons by Aedes aegypti mosquitoes, which breed in domestic and peridomestic containers (e.g., water jars, barrels, drums, tires, or tin cans) and thus in close association with humans. In areas where Ae. aegypti has been eliminated or suppressed, urban yellow fever has disappeared.
Urban yellow fever can be prevented by vaccinating human populations at risk for infection or by suppressing populations of Ae. aegypti mosquitoes so that they no longer perpetuate infection. Jungle yellow fever can most effectively be prevented by vaccination of human populations at risk for exposure.