Yellow fever

Yellow fever is a viral disease caused by the yellow fever virus (YFV), an enveloped RNA virus classified within the genus Orthoflavivirus of the Flaviviridae family. The virus is the namesake of the disease and was the first illness demonstrated to be transmissible by filtered human serum and by mosquitoes. The disease derives its common name from the characteristic jaundice that develops in severe cases, manifesting as yellowing of the skin and eyes due to hepatic involvement.

Following an incubation period of 3–6 days, yellow fever typically presents with an initial phase of fever, headache, generalized body aches particularly affecting the back, loss of appetite, nausea, vomiting, and weakness. These symptoms resolve within 3–4 days in the majority of cases. Approximately 15% of infected individuals progress to a severe toxic phase within 24 hours of initial symptom resolution, characterized by recurrence of high fever, jaundice indicating liver damage, abdominal pain, and hemorrhagic manifestations including bleeding from the mouth, nose, eyes, and gastrointestinal tract. This severe phase carries a case fatality rate of approximately 50%, with death typically occurring within 7–10 days. Kidney failure may also occur during the toxic phase. There is no specific antiviral treatment; clinical management remains supportive, focusing on rest, hydration, and management of organ failure and secondary bacterial infections.

Yellow fever is endemic to 47 countries in sub-Saharan Africa and Central/South America, with approximately 90% of reported annual cases occurring in sub-Saharan Africa. The disease exists in three distinct transmission cycles: a sylvatic (forest) cycle involving transmission between non-human primates and mosquitoes in forest canopies; a semi-domestic cycle involving transmission from forest mosquitoes to humans in jungle fringe areas; and an urban cycle involving human-to-human transmission via domestic Aedes aegypti mosquitoes. Infected travelers can export cases to countries free of yellow fever, though establishment of transmission in new areas requires the presence of competent mosquito vectors, suitable climatic conditions, and maintenance of the virus in animal reservoirs. The disease is considered high-impact and poses a potential threat to global health security due to its epidemic potential and capacity for international spread.

Yellow fever is transmitted to humans through the bite of infected mosquitoes, primarily species within the Aedes, Haemagogus, and Sabethes genera. Aedes aegypti serves as the principal vector in urban transmission cycles, while Haemagogus species are primarily associated with sylvatic transmission in jungle environments. These day-biting mosquitoes breed in domestic environments around human habitations, in forest and jungle habitats, and in semi-domestic settings. Mosquitoes become infected when they bite an infected human or non-human primate. The virus cannot be transmitted through direct person-to-person contact. The disease is maintained in nature through transmission cycles involving mosquito vectors and susceptible primate hosts.

Source-backed detail is not yet available.

Vaccination represents the most effective preventive measure against yellow fever. A single dose of the live attenuated vaccine provides lifelong immunity, with seroconversion occurring in 80–100% of recipients within 10 days and in over 99% within 30 days. Under International Health Regulations, countries may require proof of yellow fever vaccination for travelers arriving from endemic areas. Vector control measures complement vaccination efforts and include surveillance of mosquito populations, particularly Aedes aegypti, to assess urban outbreak risk. Insecticide-treated bed nets provide limited protection given the daytime biting behavior of the primary vectors. Vaccination is generally not recommended for individuals over 60 years of age without careful risk-benefit assessment, and medical exemptions require appropriate certification.

Source-backed detail is not yet available.

1. 1 WHO Health Topics. Yellow fever.
2. 2 WHO Fact Sheet. Yellow fever.
3. 3 WHO Q&A. Yellow fever.
4. 4 Wikidata. yellow fever.
5. 5 Wikipedia. Yellow fever - Wikipedia.

ICD-10

A95

ICD-11

1D48

Total cases

0

Peak month

2012-09

Coverage

2 reporting countries · 2012-09-14 → 2026-05-09