Evaluation of factors associated with positive IgM capture ELISA results in equids with clinical signs compatible with West Nile virus infection: 1,017 cases (2003).
OBJECTIVE
To describe the prevalence of West Nile virus (WNV) infection and evaluate factors associated with positive IgM capture ELISA results in equids with clinical signs compatible with WNV infection.


METHODS
Retrospective case series.


METHODS
Laboratory submission forms from 1,104 equids tested for WNV in Colorado in 2003.


METHODS
Submission forms accompanying samples submitted for detection of WNV via IgM capture ELISA were obtained from the Colorado state veterinarian and diagnostic laboratories performing the tests. Data on signalment, clinical signs, history of vaccination against WNV, and assay results were collected from laboratory submission forms. Equids with clinical signs compatible with WNV infection in which IgM capture ELISA results were positive were considered as case equids.


RESULTS
1,104 equids were tested for WNV; 1,017 (92.1%) had clinical signs compatible with WNV infection. Among equids with clinical signs compatible with WNV infection, the odds of testing positive for WNV via IgM capture ELISA were lower in males and in vaccinated equids and higher in equids with moderate and severe illness, compared with females, unvaccinated equids, and equids with mild illness.


CONCLUSIONS
Among equids with clinical signs compatible with WNV infection, vaccination against WNV, severity of clinical signs, duration of illness, and region in Colorado were associated with increased risk of having a positive IgM capture ELISA result.
Tanner
Jennifer M
JM
Animal Population Health Institute, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA.
Traub-Dargatz
Josie L
JL
Hill
Ashley E
AE
Van Campen
Hana
H
Knight
Anthony P
AP
Cunningham
Wayne E
WE
Salman
M D
MD
D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D003120:Colorado / Q000453:epidemiology; D016001:Confidence Intervals; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D005260:Female; D006734:Horse Diseases / Q000453:epidemiology*; D006736:Horses; D007075:Immunoglobulin M / Q000097:blood; D008297:Male; D016017:Odds Ratio; D012189:Retrospective Studies; D012307:Risk Factors; D016036:Seroepidemiologic Studies; D012720:Severity of Illness Index; D012737:Sex Factors; D014611:Vaccination / Q000662:veterinary; D014901:West Nile Fever / Q000453:epidemiology / Q000662:veterinary*; D014902:West Nile virus / Q000276:immunology*
D000914:Antibodies, Viral; D007075:Immunoglobulin M