Snapshot A 79-year-old man is brought to the emergency room after a trip to Texas in the summer. He was visiting extended family there where he sustained multiple mosquito bites. He reports having an intense headache and stiff neck. However, he does not exhibit signs of photophobia. He is not oriented to time or place and found to have a high-grade fever. There is no rash seen on examination. Laboratory evaluation reveals hyponatremia. (St. Louis encephalitis) Introduction Introduction flaviviruses enveloped, linear, single-stranded, positive-sense virus RNA with icosahedral capsid viruses hepatitis C virus (HCV) yellow fever virus dengue virus West Nile virus Zika virus St. Louis encephalitis virus transmission most are arboviruses and transmitted via mosquitos with the exception of HCV HCV is transmitted via blood Flaviviruses Hepatitis C Virus Yellow Fever Virus Dengue Virus West Nile Virus Zika Virus St. Louis Encephalitis Virus Clinical syndrome Hepatitis Hemorrhagic fever with hepatitis Dengue hemorrhagic fever Dengue shock syndrome West Nile fever Meningoencephalitis Zika virus infection Congenital microcephaly St. Louis encephalitis Differentiating factors Jaundice Right upper quadrant pain Jaundice Hemorrhage (epistaxis and mucosal bleeding) Blanching erythematous maculopapular rash Hemorrhage (tourniquet sign) Non-pruritic papular rash Acute flaccid paralysis with myoclonus Pruritic rash Microcephaly with intracranial calcifications Flu-like illness without a rash No photophobia St. Louis Encephalitis St Louis encephalitis virus demographics male > female most cases in the eastern and central United States risk factors exposure to endemic areas older age transmission via mosquitos from birds to humans finches and sparrows are hosts Presentation flu-like illness malaise, fever, cough, and sore throat meningoencephalitis does not present with photophobia headaches, fever, nuchal rigidity, and confusion seizures SIADH Studies detection of antibodies to the arbovirus detection of nucleic acid amplification from body fluids (CSF or blood) CSF fluid pleocytosis with a predominance of mononuclear cells normal glucose hyponatremia Treatment supportive care