Symptoms The majority of persons infected with yellow fever virus have no illness or only mild illness. In persons who develop symptoms, the incubation period (time from infection until illness) is typically 3–6 days. The initial symptoms include sudden onset of fever, chills, severe headache, back pain, general body aches, nausea, and vomiting, fatigue, and weakness. Most persons improve after the initial presentation. After a brief remission of hours to a day, roughly 15% of cases progress to develop a more severe form of the disease. The severe form is characterized by high fever, jaundice, bleeding, and eventually shock and failure of multiple organs.

An infectious disease, yellow fever infects humans, all species of monkeys, and certain other small mammals. The virus is transmitted from animals to humans and among humans by several species of mosquitoes. Yellow fever is one of the great epidemic diseases of the tropical world, and in earlier centuries it was one of the great plagues of the New World. At one time the tropical and subtropical regions of the Americas were subjected to devastating epidemics, and serious outbreaks occurred not only as far north as Philadelphia, New York, and Boston but also as far away as Spain, France, England, and Italy.

Yellow fever is diagnosed clinically, with laboratory confirmatory testing available.

Yellow fever is diagnosed clinically, with laboratory confirmatory testing available.