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Eastern equine encephalitis (EEE) and Venezuelan equine encephalitis (VEE) are associated with severe morbidity and mortality in equines and humans. In the U.S., EEE is both the least frequent and the most lethal of the principal arbovirus encephalitides.
To examine features of an outbreak of encephalitis in humans and horses in Darién, an eastern province of Panama, researchers identified 19 patients with encephalitis admitted to the hospital during the outbreak. Among the 11 confirmed cases (almost all in children), 7 had EEE, 3 had VEE, and 1 had both. Three patients died, 1 of whom had confirmed VEE. Clinical findings included brain lesions, seizures, and neurological sequelae. An additional 99 cases of suspected alphavirus infection were detected during surveillance. Thirteen cases were confirmed as EEE, 11 cases as VEE and 1 case as dual infection. Fifty cases in horses were confirmed as EEE and 8 as VEE.
Carrera J-P et al. Eastern equine encephalitis in Latin America. N Engl J Med 2013 Aug 22; 369:732. (http://dx.doi.org/10.1056/NEJMoa1212628)
Comment
Symptoms of eastern equine encephalitis include fever, myalgia, arthralgia, retroocular pain, headache, and decreased consciousness, followed by neurological disease, with the possibility of paralysis, seizures, and coma (N Engl J Med 1997; 336:1867). An estimated 30% of patients die, and mild-to-severe long-term neurological deficits occur in about one quarter of survivors. By comparison, Venezuelan equine encephalitis viruses typically cause a mild-to-severe flu-like illness, and neurological disease develops in only 4% to 14% of symptomatic cases, with few fatalities (J Virol 2008; 82:10634).
This study, although very interesting, is not necessarily representative of all Latin America, where EEE is common in equids, but only three cases were recognized previously in humans. VEE and EEE are difficult to distinguish from dengue and other arboviral diseases, and confirmatory testing is often too costly to perform in Latin America (Future Virol 2011; 6:721). We need surveillance systems that conduct follow-up of patients seen during the acute illness, to identify and track subsequent neurological signs and symptoms.