An acute infectious disease characterized by jaundice, epigastric tenderness, vomiting, hemorrhages, and a febrile course consisting of two paroxysms. There are two forms of yellow fever: urban, in which the transmission cycle is mosquito; and sylvan, in which the reservoir is wild primates. Also, in sylvan yellow fever, the mosquito will remain infected for life. Except for a few cases in Trinidad in 1954, urban yellow fever has not been reported in North or South America since 1942. Outbreaks do occur in Africa adjacent to rain forests. Yellow fever has not been reported in Asia or eastern coast of Africa. Sylvan yellow fever is enzootic in South America and parts of Africa.