Snapshot A 43-year-old female presents to the ED with a six day history of fever, chills, headache, and severe backache. She returned from Gambia on a missions trip 10 days prior to onset of illness. She had been taking antimalarial prophylaxis but did not receive any immunizations prior to the trip. Temperature is 102.8°F (39°C). Physical exam reveals an ill-looking woman with pallor and scleral icterus.Her epigastrium is markedly tender to palpation. Complete blood count shows a hematocrit of 30%, platelets of 75,000/mm3, and leukocyte count of 3,200/mm3. Coagualtion panel revealed an INR of 5.3 and PT of 29 secs. Total bilirubin was 3.3 mg/dL, AST 950 U/L, and ALT 350 U/L. Blood, CSF, and urine cultures were negative. No Plasmodia were detected on peripheral blood smear. Patient was presumptively treated for malaria and serology for IgM ELISA is pending. Introduction Classification linear, enveloped (+) ssRNA flavivirus yellow fever virus Acute viral hemorrhagic fever spread by infected mosquitos flavi = yellow, jaundice Epidemiology incidence 200,000 illnesses per year 30,000 deaths per year risk factors residing in Africa 90% of infections take place in Africa the unvaccinated population location common in Africa and South America Transmission 3 types sylvatic (or jungle) occurs in tropical rainforests infected monkeys pass virus to other mosquitos that feed on them these mosquitos bite and infect humans in the forest (think loggers) intermediate occurs in humid savannahs of Africa small-scale epidemics in rural villages semi-domestic mosquitos infect both monkey and human hosts increased contact between man and infected mosquito urban large explosive epidemics travellers from rural areas introduce virus into highly populated areas mosquito can carry virus from person to person via Aedes aegypti mosquito virus has monkey or human reservoir Pathogenesis virus replicates in lymph nodes infects dendritic cells in particular find their way to the liver where they infect hepatocytes eosinophilic degradation and cytokine release necrotic masses (Councilman bodies) are found in the cytoplasm of hepatocytes Presentation Symptoms incubation period of virus is approximately 3-6 days mild (lasts approximately 3-4 days) fever headache nausea vomiting myalgias anorexia possible subsequent toxic phase recurring fever liver damage leading to jaundice and/or death bleeding daithesis bloody vomitus affects 15% of those with a primary infection fatal in 20% of cases Evaluation Biopsy liver can verify inflammation, necrosis, and viral antigens only consider bx post-mortem b/c of bleeding tendency of yellow fever patients Diagnosis clinical diagnosis relies on history, symptomatology, and incubation time viral genome amplification via RT-PCR (reverse transcription polymerase chain reaction) cannot be confirmed until 6-10 days after illness began viral growth in cell culture takes 1-4 weeks ELISA IgM against yellow fever virus can cross-react with other flaviviruses Differential Other viral hemorrhagic fevers (Ebola, Marburg, and Lassa) not usually associated with jaundice Viral hepatitis A and B Leptospirosis Treatment Supportive care no specific treatments have been developed yet hospitalization as needed Prognosis, Prevention, and Complications Prognosis mortality 20-60% in developing countries (mainly unvaccinated population) Prevention vaccines YF-VAX live, attenuated induces humoral and cell-mediated immunity q10 years PRN needed for travel to affected areas vector control insect repellant