Posted by Vector and Vector-borne Disease Committee
June 21, 2022
- Erin Staples,1* Katherine B. Gibney,1,2, Amanda J. Panella,1 Harry E. Prince,3 Alison J. Basile,1 Janeen Laven,1 James J. Sejvar,4 and Marc Fischer1
1Arboviral Diseases Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado; 2Epidemic Intelligence Service Program, CDC, Atlanta, Georgia; 3Quest Diagnostics Infectious Disease, Inc., San Juan Capistrano, California; 4Division ofHigh-Consequence Pathogens and Pathology, CDC, Atlanta, Georgia
Am. J. Trop. Med. Hyg.; doi:10.4269/ajtmh.21-1234
Abstract. West Nile virus (WNV) IgM antibodies typically indicate a recent infection. However, WNV IgM antibodies can remain detectable for months to years following illness onset. We found that 23% (11/47) of samples tested with a WNV ELISA and 43% (20/47) of samples tested with WNV microsphere immunoassay (MIA) at 16–19 months following WNV illness onset were positive for IgM antibodies. The proportion of samples testing positive for WNV IgM by ELISA decreased over time, but 5% (2/44) of individuals remained positive at 60–63 months after their acute illness and 4% (2/50) were WNV IgM equivocal at 72–81 months. Clinicians and public health officials should consider these findings along with clinical and epidemiologic data when interpreting WNV IgM antibody test results.
Note: WNV surveillance programs frequently make decisions concerning adulticide applications based on reported human cases. This study indicates that laboratory confirmation of suspect cases based on IgM ELISA could be the result of previous exposure and not due to recent infection. Careful evaluation of case data combined with mosquito and mosquito infection data should be included in application decisions.