Evaluation of immunoglobulin M (IgM) and IgG enzyme immunoassays in serologic diagnosis of West Nile virus infection

A unique urban encephalitis epidemic in Romania signaled the emergence of n eurological infection due to West Nile (WN) virus as a novel public health threat in Eastern Europe and provided an opportunity to evaluate patterns o f immunoglobulin G (IgG) and IgM reactivity in IgM capture and IgG enzyme-l inked immunosorbent assays (ELISAs). WN virus infection was diagnosed scrol ogically in 236 of 290 patients from whom acute serum or cerebrospinal flui d (CSF) samples were available. In 37% of serum samples and in 258 of CSF s amples collected in the first week of illness, anti-WN virus IgM antibody w as detected in the absence of virus-specific Igc, The switch to an IgG anti body response occurred after 4 to 5 days of illness and earlier in CSF than in serum. A specific humoral immune response was detected in the CSF befor e the serum in some patients for whom paired CSF and serum samples from the same day were available. IBM antibody in convalescent serum samples persis ted beyond 2 months after the onset of illness in more than 50% of patients . ELISA optical density values and antibody concentrations were well correl ated for both IgM and IgG immunoassays. Anti-WN virus IgM antibody in acute -phase samples did not cross-react significantly with flaviviruses in other antigenic groups.