Specificity of immunoglobulin M and G antibody responses in humans infected with eastern and western equine encephalitis viruses: application to rapid serodiagnosis.

Paired sera from 20 humans with eastern equine encephalitis (EEE) virus infections and from 17 humans with western equine encephalitis (WEE) virus infections, all with previously demonstrated fourfold or greater rises or falls in hemagglutination-inhibiting, complement-fixing, or neutralizing antibody titers, were tested for immunoglobulin M (IgM) and IgG antibodies by an enzyme immunoassay. All individuals with EEE and 14 of 17 individuals with WEE had IgM antibody, some as early as 1 day after onset. Two of the three persons with WEE who did not develop IgM antibody died. IgM antibody declined but persisted for at least 3 months after the onset of illness in one individual each with EEE and WEE. IgG antibody was not detected until the middle of week 2 after onset. The sensitivity of the IgM antibody capture enzyme immunoassay described and the specificity, as shown by the absence of heterologous alphavirus reactivity, indicate that this is the test of choice for the rapid diagnosis of human infections caused by EEE and WEE viruses.