Rapid diagnosis of LaCrosse encephalitis: detection of specific immunoglobulin M in cerebrospinal fluid.

An immunoglobulin M (IgM) antibody capture enzyme immunoassay (MAC-EIA) was developed for the rapid and early diagnosis of LaCrosse (LAC) virus infections. The MAC-EIA was a sensitive and specific technique for the detection of IgM antibodies to LAC virus in cerebrospinal fluid specimens and in acute-phase serum specimens. In a retrospective study, cerebrospinal fluid and acute-phase serum paired samples from 108 patients were tested by the MAC-EIA and by an IgM immunofluorescence assay. The results were compared with the original diagnosis, which was made by using a variety of classical serological tests including serum neutralization, hemagglutination inhibition, and complement fixation. Thirty patients were confirmed as having LAC virus infections; of these, 30 (100%) were diagnosed as positive by serum MAC-EIA, and 27 (90%) were positive by cerebrospinal fluid MAC-EIA. The MAC-EIA was more sensitive than the IgM immunofluorescence assay. Two patients who were not previously confirmed as positive cases were diagnosed as having LAC virus infections by the MAC-EIA. One patient who was subsequently diagnosed as having a Jamestown Canyon virus infection and two patients who were previously infected with Jamestown Canyon virus were not falsely identified as having LAC virus infections by the MAC-EIA.