Rapid and specific serodiagnosis of western equine encephalitis virus infection in horses

Abstract

SUMMARY Paired sera from 28 nonvaccinated horses with serologically confirmed western equine encephalitis ( wee ) virus infections were evaluated for immunoglobulin (Ig)M and IgG directed against wee virus, by use of enzyme immunoassay. Twenty-one of the horses developed ≥ 4-fold increases or decreases in serum IgM titers in paired serum samples, confirming the diagnosis of wee in these horses. Of the remaining 7 horses, 1 had stable IgM titers, 1 had a 2-fold increase in IgM titer between paired sera, 2 had 2-fold decreases in IgM titer, and for 3 horses adequate volumes were not available for both sera of the pair. Twenty-nine of 56 blood samples collected from these 28 horses had been collected within the first 3 days after clinical disease was recognized; all 28 horses and 48 of 53 available serum samples had IgM antibody to wee virus. Immunoglobulin M also was detected in sera of 27 of 45 other nonvaccinated horses that had illnesses clinically compatible with wee . Sera with IgM did not have cross-reacting IgM against eastern equine encephalitis virus. Therefore, the sensitivity, specificity, and lack of persistence of IgM was useful in the rapid diagnosis of wee virus infections in horses.