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Yellow fever
is a mosquito-borne flavivirus infection endemic in tropical South
America and sub-Saharan Africa. Symptoms may include sudden onset
of fever, relative bradycardia, headache, and, if severe, jaundice,
hemorrhage, and multiple organ failure. Diagnosis is with viral
culture and serologic tests. Prevention involves vaccination and
mosquito control. Treatment is supportive.
In urban yellow fever, virus is transmitted by the bite of an Aedes
aegypti mosquito infected about 2 wk previously by feeding on a viremic person. In jungle (sylvatic) yellow fever, the virus is transmitted by Haemagogus and other forest canopy mosquitoes that acquire the virus from wild primates. Incidence is highest during months of peak rainfall, humidity, and temperature in South America and during the late rainy and early dry seasons in Africa.
Symptoms and Signs
Infection ranges from asymptomatic (in 5 to 50% of cases) to a hemorrhagic fever with 50% mortality. Incubation lasts 3 to 6 days. Onset is sudden, with fever of 39 to 40° C, chills, headache, dizziness, and myalgias. The pulse, usually rapid initially, by the 2nd day becomes slow for the degree of fever (Faget's sign). The face is flushed and the eyes are injected. Nausea, vomiting, constipation, severe prostration, restlessness, and irritability are common. Mild disease may resolve after 1 to 3 days. In moderate or severe cases, however, the fever falls suddenly 2 to 5 days after onset, and a remission of several hours or days ensues. The fever recurs, but the pulse remains slow. Jaundice, extreme albuminuria, and epigastric tenderness with hematemesis often occur together after 5 days of illness. There may be oliguria, petechiae, mucosal hemorrhages, confusion, and apathy.
Disease may last > 1 wk with rapid recovery and no sequelae. In the most severe (malignant) cases, delirium, intractable hiccups, seizures, coma, and multiple organ failure may occur terminally. During recovery, bacterial superinfections, particularly pneumonia, can occur.
Diagnosis
Yellow fever is suspected in patients in endemic areas who develop sudden fever with relative bradycardia and jaundice; mild disease often escapes diagnosis. CBC, urinalysis, liver function tests, coagulation tests, viral blood culture, and serologic tests should be obtained. Leukopenia with a relative neutropenia is common, as are thrombocytopenia, prolonged clotting, and increased PT. Bilirubin and aminotransferase levels may be elevated acutely and for several months. Albuminuria, which occurs in 90% of patients, may reach 20 g/L; it helps differentiate yellow fever from hepatitis. In the most severe form, called malignant yellow fever, hypoglycemia and hyperkalemia may occur terminally.
Diagnosis is confirmed by culture, serologic tests, PCR, or by finding characteristic midzonal hepatocyte necrosis at autopsy. Suspected or confirmed cases must be quarantined. Needle biopsy of the liver during illness is contraindicated by the risk of hemorrhage.
Prognosis
and Treatment
Up to 10% of patients with disease severe enough to be diagnosed die.
Treatment is mainly supportive. Bleeding may be treated with Ca gluconate 1 g IV once or twice/day or with phytonadione . Prophylaxis against GI bleeding with a proton pump inhibitor or an H2 blocker should be used in all patients ill enough to require hospitalization.
Prevention
The most effective way to prevent outbreaks is to reduce the number of mosquitoes and limit mosquito bites by using diethyltoluamide (DEET), mosquito netting, and protective attire. During jungle outbreaks, people should evacuate the area until they are immunized and mosquitoes are controlled. For people traveling to endemic areas, active immunization with the 17D strain of live, attenuated yellow fever vaccine (0.5 mL sc q 10 yr) is indicated and is effective in 95%. In the US, the vaccine is given only at US Public Health Service–authorized Yellow Fever Vaccination Centers. The vaccine is contraindicated in pregnant women and in those with compromised immunity.
To prevent further mosquito transmission, infected patients should be isolated in rooms that are well screened and sprayed with insecticides.
Last full review/revision November 2005
Content last modified November 2005
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