Laboratory Diagnosis of West Nile Virus

Laboratory Diagnosis of West Nile Virus: The University of Iowa Hygienic Laboratory (UHL) is performing serologic testing (IgG and IgM) for West Nile virus using an indirect fluorescent antibody assay (IFA) on serum. Because of potential cross reactivity with other flaviruses (such as St. Louis encephalitis virus) a plaque reduction neutralization assay is required for confirmation of a positive IFA or ELISA result. If a patient has a positive antibody test on serum and CSF is available, UHL has an ELISA that they will perform on serum and CSF. This UHL policy is based on the lower level of antibody that has been detected in CSF in comparison to serum in documented cases. The presence of IgM antibody in CSF offers support that the serum antibody is a true positive. Serum IgM may persist as long as 500 days post infection, so patient history is important and should include date of onset of symptoms, travel history, and vaccination history (individuals who have been vaccinated against Yellow Fever may have antibodies that cross react with West Nile virus serologic assays). The only PCR testing currently being performed at UHL is on animal specimens. UHL has initiated development of a PCR assay for human CSF specimens; however, it is not known when this test will be available. For more information, including a webcast for clinicians originally broadcast 8/8/2002, consult the Center for Disease Control and Prevention (CDC) website.

Specimen for IgG and IgM detection in serum by IFA: 3 ml red top (1.5 ml minimum); performed once weekly (Thursday).

Questions regarding the laboratory diagnosis of West Nile virus may be directed to Dr. Gary Doern (356-8616) or Dr. Sandra Richter (356-2990).