Yellow fever is a mosquito-borne viral infection of the Flaviviridae family. The disease is endemic to equatorial regions of Africa, South America, and Central America. The mortality rate of yellow fever in general is 8%; however, patients that develop severe disease have a mortality rate of 20%-50%.

The incubation period of yellow fever is 3-6 days, and many cases are mild or asymptomatic. Symptomatic patients experience a sudden onset of fever, chills, myalgia, headache, facial flushing, prominent low back pain, conjunctival redness, loss of appetite, and nausea / vomiting, which lasts for 3-4 days. This is followed by a period of remission with resolution of symptoms for 48 hours, and approximately 85% of patients will clear the infection at this stage.

The remaining 15% of patients will develop a hemorrhagic disease (malignant yellow fever) consisting of hepatitis, jaundice, abdominal pain, hematemesis, melena, petechiae, and hemorrhaging from the mouth, nose, and eyes. Fever recurs with relative bradycardia. Renal dysfunction often occurs, resulting in anuria. Disseminated intravascular coagulopathy, myocarditis, seizures, and coma may occur. Mortality varies according to level of supportive care received: up to 50% of patients in this phase will die within 2 weeks.

Person-to-person transmission is not possible. Aedes, Haemagogus, and Sabethes mosquitoes are the vectors, and forest monkeys are reservoirs of the disease.