Eastern equine encephalitis

Eastern equine encephalitis (EEE), also called triple E and sleeping sickness, is a viral disease caused mainly by the Eastern equine encephalitis virus (EEEV). Most infections in humans are asymptomatic, but about 5% of the time the infection progresses to severe neuroinvasive disease. Symptoms typically appear 3–10 days after being bitten by an infected mosquito and initially include fever, headache, nausea, vomiting, fatigue, muscle pain, and joint pain. Neurological symptoms usually appear a few days later and include altered mental state, encephalitis, photophobia, seizures, paralysis, and loss of consciousness and coma. The case fatality rate is 30–75% depending on age, with disease severity greatest in young children and the elderly. About 50 to 90% of survivors experience long-term neurological complications that range from minor to severe. EEE is most common in horses, in which the disease carries a 70–90% case fatality rate and permanent brain damage for survivors. Most human cases are caused by EEEV. Traditionally, four lineages of EEEV were recognized: I, II, III, and IV. Lineage I corresponds to EEEV and the other lineages are classified as a different virus: Madariaga virus (MADV). EEEV is found in North America, the Caribbean, and Central America, and MADV is found in Central America and South America. While both EEEV and MADV cause disease in horses, it is very rare for MADV to cause disease in humans. EEEV and MADV are single-stranded, positive-sense RNA viruses of the genus Alphavirus in the family Togaviridae. Alphaviruses are sorted into Old World alphaviruses and New World alphaviruses, and considered arthritogenic (affecting the joints) or encephalitic (affecting the brain). EEEV and MADV are New World encephalitic alphaviruses. Among encephalitic alphaviruses, EEEV causes the most severe disease in humans. EEEV is maintained in nature in an enzootic cycle between natural reservoirs of the virus and mosquitos...