Yellow Fever Virus
Yellow fever virus is a mosquito-borne flavivirus (arborvirus) that causes yellow fever in South America and sub-Saharan Africa. Yellow fever is the most severe arbovirus to circulate in the Americas. Yellow fever infections are referred to as sylvatic or jungle cases because the typical transmission cycle occurs between forest mosquitoes and forest dwelling nonhuman primates. Humans serve as incidental hosts. So far, there has been no evidence of human-to-human transmission by Aedes aegypti mosquitoes.
An outbreak of yellow fever began in Brazil in December 2016 involving both humans and nonhuman primates. As of February 28, 2018, more than 1300 yellow fever infections, including more than 400 deaths, have been confirmed in Brazil. Ten travel-related cases have been reported in unvaccinated individuals since January 2018. Yellow fever outbreaks could conceivably occur in the U.S. territories, just as the Zika epidemic reached Puerto Rico.
Clinical illness manifests itself in three stages: infection, remission, and intoxication. During the infection stage, patients present after a 3 to6-day incubation period with a nonspecific flulike illness. Symptoms may include fever, headache, malaise, nausea, vomiting, diarrhea, rash, myalgia, and arthralgia. High fevers associated with bradycardia, leukopenia, thrombocytopenia and elevated hepatic transaminases may provide a clue to the diagnosis. Patients are viremic during this stage.
The infection stage is followed by a period of remission, when most patients fully recover. However, 15 to 20% of patients progress to the intoxication stage, in which symptoms recur after 24 to 48 hours.This stage is characterized by high fever, hemorrhage, liver failure with jaundice, renal failure, encephalopathy and shock. Among the 15% of patients who develop severe illness, the case fatality rate is 20%–60%. Yellow fever virus antibodies may be detected during this stage, but viremia has usually cleared.
Diagnostic tests include real time PCR and serologic tests for yellow fever virus. PCR is the best test for detecting Yellow fever during the infection stage. Yellow fever IgM and IgG serology is the preferred test for diagnostic confirmation during the intoxication stage.
References
Hamer DH, Angelo K, Caumes E, et al. Fatal Yellow Fever in Travelers to Brazil, 2018. MMWR Morb Mortal Wkly Rep. ePub: 16 March 2018. DOI: http://dx.doi.org/10.15585/mmwr.mm6711e1
Paules CI and Fauci AS. Yellow fever – Once again on the radar screen in the Americas. New Engl J Med. 2017;376:1397-98.
