Summary
Yellow fever is an acute viral infection caused by the yellow fever virus. Primates are the main reservoir of the virus, which is usually transmitted through bites from infected mosquitoes. Yellow fever is endemic in large parts of South America and Africa. The incubation period is 3–6 days, and the majority of patients remain asymptomatic or experience only mild symptoms. Symptomatic patients initially present with nonspecific symptoms such as sudden-onset fever, malaise, headaches, chills, nausea, and myalgia. Approx. 15% of symptomatic patients progress to the most serious stage of the disease, which can present with life-threatening hemorrhagic fever and organ failure. There is no causal treatment available, making prevention of crucial importance. A single dose of live-attenuated vaccine provides lifelong protection for most individuals.
Epidemiology
- Yellow fever is endemic in tropical regions of South America and Sub-Saharan Africa.
- Asia, Europe, North America, and Australia are free of yellow fever (except for occasional imported cases).
Yellow fever is endemic in large parts of South America and Africa.
References:[1]
Epidemiological data refers to the US, unless otherwise specified.
Etiology
-
Pathogen: yellow fever virus
- Genus: flavivirus, type of arbovirus
- Genetics: single-stranded, positive-sense, linear RNA virus
- Appearance: enveloped, icosahedral
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Transmission
- Vectors: mosquitoes; (primarily Aedes aegypti )
- Main reservoir: primates (human and non-human)
- Different transmission cycles (depending on local circumstances and geography)
References:[2][3]
Clinical features
- Incubation time: 3–6 days
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Clinical features
- The majority of infected individuals remain asymptomatic.
-
In symptomatic patients: classic progression in three stages
- Period of infection (3–4 days)
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Period of remission (up to 2 days)
- Easing of symptoms and decline in fever
- Period of intoxication (only in ∼ 15% of symptomatic patients)
Most patients remain asymptomatic or experience only mild symptoms.
References:[4][5]
Diagnostics
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Laboratory tests
- ↑ ALT/AST
- Leukopenia
- In period of intoxication
- Thrombocytopenia, ↑ PTT
- Signs of organ failure (see acute liver failure, acute renal failure)
- Virus detection
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Liver biopsy
- Used for definitive diagnosis (e.g., postmortem)
- Must not be done while the patient has an active yellow fever infection
- May show Councilman bodies (eosinophilic apoptotic globules)
The best test to rule out yellow fever infection is PCR, particularly in the absence of overt symptoms such as fever, headaches, and chills.
References:[2]
Differential diagnoses
- Influenza
- Viral hepatitis (e.g., hepatitis A)
- Other viral hemorrhagic fevers (e.g., Dengue hemorrhagic fever)
- Malaria
The differential diagnoses listed here are not exhaustive.
Treatment
Complications
- Bacterial superinfections (e.g., pneumonia, sepsis)
- Cardiac disorders (e.g., myocarditis)
We list the most important complications. The selection is not exhaustive.
Prevention
Vaccination
- Indication: recommended for individuals (≥ 9 months) traveling to areas where yellow fever is endemic
- Administration: See “Vaccines before travel” for details.
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Absolute contraindications: (also see general contraindications for vaccination)
- Infants under 9 months of age
- Individuals with insufficient immune function (e.g., due to HIV infection or immunosuppressive medication)
References:[2][6]