Yellow fever
Yellow fever is a mosquito-borne flavivirus hemorrhagic fever of sub-Saharan Africa and tropical South America in which an abrupt febrile illness can, after a brief remission, progress to jaundice, kidney injury, coagulopathy, hemorrhage, and shock, with 30% to 60% mortality in severe disease. Diagnosis is by RT-PCR early or IgM antibody later, treatment is supportive, and a single dose of live attenuated vaccine, contraindicated in immunocompromised and pregnant persons, prevents it.
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What this article covers
- Overview
A mosquito-borne viral hemorrhagic fever: yellow fever virus is a flavivirus in the viral hemorrhagic fever group, transmitted by Aedes mosquitoes in sub-Saharan Africa and tropical South America.
- Epidemiology
Severe disease mortality is 30% to 60%, placing yellow fever among the deadliest vaccine-preventable travel infections.
- Risk factors
Unvaccinated travel to or residence in an endemic area of Africa or South America, the dominant risk.
- Pathophysiology
Mosquito inoculation from a primate or human reservoir: Aedes mosquitoes carry the virus from infected monkeys (sylvatic cycle) or infected humans (urban cycle).
- Clinical features
Biphasic course (the hallmark): abrupt fever, headache, myalgia, nausea, and vomiting, then a brief remission, after which some patients enter a toxic phase with jaundice, kidney injury, coagulopathy, and shock.
- Differential diagnosis
Malaria: the most common cause of fever in returning travelers; paroxysmal fever every 48 or 72 hours (continuous with Plasmodium falciparum) and intraerythrocytic parasites on blood smear.
- Diagnosis
Yellow fever is confirmed by detecting the virus or a specific antibody: there are no formal clinical criteria; in a patient with exposure in sub-Saharan Africa or tropical South America and a…
- Management
First, admit any patient in the toxic phase (jaundice, kidney injury, coagulopathy, or shock) to intensive care, because there is no antiviral therapy and treatment is organ support.
- Complications
Hemorrhagic shock: the terminal event in fatal severe disease.
- Prognosis
Severe disease carries 30% to 60% mortality, concentrated in patients who enter the toxic phase.
- Prevention
Vaccinate every eligible traveler to an endemic area of Africa or South America with a single dose of live attenuated yellow fever vaccine, which needs no booster and protects nearly completely.
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Dengue is a flavivirus spread by daytime-feeding Aedes mosquitoes that causes an acute febrile illness with retro-orbital pain and severe myalgia, and can progress to hemorrhagic fever and shock, especially on heterotypic secondary infection; management is supportive with acetaminophen and fluids, avoiding NSAIDs and aspirin.
- Malaria
Malaria is a Plasmodium infection acquired from Anopheles mosquito bites, most often diagnosed in returning travelers from sub-Saharan Africa, and severe Plasmodium falciparum disease is a medical emergency treated with IV artesunate.
- Leptospirosis
Leptospirosis is a zoonotic spirochetal infection from water or soil contaminated with infected-animal urine, causing a biphasic illness with conjunctival suffusion and calf/lumbar myalgia, occasionally progressing to Weil disease with jaundice and renal failure, diagnosed clinically and confirmed by culture, serology, or PCR, and treated with doxycycline or, in severe disease, IV penicillin or ceftriaxone.
- Ebola virus disease
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- Hepatitis A virus infection
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- Hepatitis E virus infection
Hepatitis E virus is a fecal-oral or foodborne RNA virus with four genotypes that usually causes self-limited acute hepatitis resembling hepatitis A, but carries a high mortality risk in pregnant patients and can become chronic in immunocompromised hosts, especially solid-organ transplant recipients. Diagnosis rests on HEV IgM or RNA, treatment is supportive for acute disease and ribavirin for chronic infection, and prevention is safe water and thoroughly cooked pork or venison.
- Acute liver failure
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- Vaccines
Vaccines are live attenuated, inactivated, subunit, conjugate, or toxoid preparations that induce antigen-specific active immunity to prevent infection or its complications before exposure occurs. Selection follows the age- and risk-based Advisory Committee on Immunization Practices schedule, with routine adult boosting such as Tdap every 10 years, and inactivated regimens substituted whenever a live vaccine is contraindicated by pregnancy or immunosuppression.