Snapshot A 32-year-old woman presents to a local clinic in Nigeria. She had been working in the rainforest as part of a conservation movement and had been bitten multiple times over the past few days by mosquitos and other flying insects. Three days ago, she developed a flu-like viral illness and recently began having minor nosebleeds. She also noted that her skin looked more yellow than normal. On exam, she is jaundiced with scleral icterus. She is also noted to have hepatomegaly and gingival bleeding. Laboratory testing reveals a transaminitis and hyperbilirubinemia. She is told that she needs to be admitted for close monitoring. Introduction Classification yellow fever virus a positive-stranded, linear RNA virus a flavivirus and arbovirus with icosahedral capsid transmitted by Aedes mosquito reservoir is human or monkey Pathogenesis the virus spreads via blood it infects the liver liver cells die via apoptosis coagulopathy occurs due to loss of hepatic synthesis of clotting factors Epidemiology Incidence endemic in South America and Africa Risk factors exposure to endemic areas mosquito bites Presentation Symptoms most patients are asymptomatic if symptomatic flu-like prodrome headache myalgias nausea black vomitus Physical exam high fever jaundice scleral icterus hepatomegaly minor hemorrhage epistaxis mucosal bleeding melena Studies Labs diagnostic reverse transcriptase-polymerase chain reaction serology with enzyme-linked immunosorbent assay transaminitis (AST > ALT) elevated prothrombin and partial thromboplastin times hyperbilirubinemia Guaiac stool testing occult blood Liver biopsy Councilman bodies eosinophilic apoptotic globules typically found on autopsy Making the diagnosis most cases are clinically diagnosed, especially in those who have recently traveled to an endemic area Differential Dengue fever distinguishing factor may also be hemorrhagic but does not affect the liver will not present with jaundice, scleral icterus, and hepatomegaly Chikungunya distinguishing factor typically does not present with hemorrhage Treatment Conservative supportive care indication all patients modalities rehydration close monitoring pain control Associated conditions hemorrhagic fever Prevention Live-attenuated virus vaccine given at age 9-12 months in endemic areas given 10 days prior to travel to endemic areas Complications Shock Death Prolonged weakness and fatigue Prognosis Most patients recover without complications However, in severe cases, mortality rate is up to 60%