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 who develop severe disease have a mortality rate of 20%-50%.

Although the use of yellow fever as an agent of bioterrorism is unlikely, in a bioterrorist attack it would most likely be dispersed as an aerosol; the release of infected mosquitoes is also feasible. Mosquitoes serve as the natural reservoir and vector: Aedes spp in Africa and Haemagogus and Sabethes spp in South America.

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 injection, 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 bleeding from mucous membranes. Fever recurs with relative bradycardia. Renal dysfunction often occurs resulting in anuria. Up to 50% of patients in the toxic phase will die within 2 weeks. Those who recover experience months of fatigue and have lasting immunity to reinfection.

Person-to-person transmission is not possible, although transmission through exposure to blood, bodily fluids, or tissues in the setting of laboratory sample handling has been documented.

A vaccine for yellow fever is available. Refer to Management Pearls.