Microbiology · RNA arboviruses
Yellow fever virus !
- Virus
- Enveloped
- Exam priority: high
A flavivirus kept alive by monkeys and forest mosquitoes. It can cause jaundice, bleeding and organ failure; one vaccine dose protects for life.
Updated 2026-11-01
Also called: YFV
At a glance
- Shape
- Spherical, icosahedral capsid
- Genome
- Single-stranded, positive-sense RNA
- Envelope
- Enveloped
- Family
- Flaviviridae, genus Orthoflavivirus
- Size
- About 40 to 50 nm
Morphology
- Enveloped virus with protein E; a single serotype
- The prototype flavivirus that names the family (flavus, yellow)
Transmission
- Sylvatic cycle: Haemagogus and Sabethes mosquitoes among monkeys; humans are infected on entering the forest
- Intermediate cycle: semi-domestic mosquitoes in rural areas near forest
- Urban cycle: Aedes aegypti from person to person, the highest epidemic risk
Reservoir: Non-human primates (howler monkeys, among others); Mosquitoes, which stay infected for life
Vector: Haemagogus and Sabethes (sylvatic); Aedes aegypti (urban)
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Liver tropism: midzonal lobular necrosis with Councilman (apoptotic) bodies
- Liver damage causes jaundice and coagulopathy
- Kidney and heart injury and shock in the toxic phase
Diseases it causes
- Yellow fever: mild form and toxic phase with jaundice, bleeding and kidney failure Yellow fever →
Clinical picture
- Many infections are mild: fever, headache, myalgia, nausea
- Faget sign: high fever with a relatively slow pulse
- Brief remission and then, in a share of cases, a toxic phase with jaundice, bleeding (black vomit), kidney failure and shock
- About half of patients in the toxic phase die within 7 to 10 days
Diagnosis
- RT-PCR on blood early in illness
- IgM by ELISA and neutralization tests later
- Very high transaminases and bilirubin, albuminuria
- Vaccination and forest travel history; cross-reaction with other flaviviruses
Treatment
There is no specific antiviral: care is supportive in a unit able to manage liver and kidney failure and bleeding. Aspirin and NSAIDs are avoided.
Drug class only; doses and regimens are set by the clinician from the current guideline.
Prevention
- Live attenuated vaccine (17D strain): one dose gives lifelong protection
- Bite protection and Aedes aegypti control in cities
- Epizootic surveillance: monkey deaths warn of virus circulation
Vaccine: Live attenuated 17D vaccine, single dose with lifelong immunity; it is in Colombia's childhood PAI schedule and offered to people living in or travelling to risk areas. It is not advised under 9 months, in pregnancy (except in outbreaks), with severe egg allergy or severe immunosuppression. Some countries require the international certificate of vaccination from travellers.
Test yourself
Think of the answer, then tap the question to see it.
What is the main transmission cycle of yellow fever in the Americas?
The sylvatic cycle: Haemagogus and Sabethes mosquitoes pass the virus among monkeys, and people are infected when they enter the forest or its edges.
Which liver histology finding is classic for yellow fever?
Midzonal lobular necrosis with Councilman bodies (apoptotic hepatocytes).
How many vaccine doses give lifelong protection?
A single dose of the live attenuated 17D vaccine; WHO says no booster is needed.
What is the Faget sign?
High fever with a relatively slow pulse, described in yellow fever.
Related
Related conditions
← Back to the group: RNA arboviruses
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Yellow fever (World Health Organization (WHO), 2025); Yellow Fever (Pan American Health Organization (PAHO), 2025); Appendix A: Type and Duration of Precautions Recommended for Selected Infections and Conditions (CDC, 2024).
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Representative model, for educational purposes only.