Diagnostic performance of the equine IgM capture ELISA for serodiagnosis of West Nile virus infection.
Authors: Long Maureen T, Jeter William, Hernandez Jorge, Sellon Debra C, Gosche David, Gillis Karen, Bille Emily, Gibbs E Paul
Journal: Journal of veterinary internal medicine
Summary
# West Nile Virus Serology in Horses: Validating the IgM Capture ELISA West Nile virus presents a significant disease threat to equine populations, but accurate serological diagnosis depends on reliable testing methods; this 2006 study evaluated the diagnostic performance of the IgM capture ELISA (MAC) in 36 confirmed infected horses and 383 uninfected controls across multiple populations. Using receiver operating curve analysis, the researchers assessed sensitivity and specificity at various cutoff points, ultimately demonstrating that at a standard cutoff of 2.0, the MAC achieved 91.7% sensitivity and 99.2% specificity, with an area under the curve of 0.95. When applied to 602 field samples from suspect cases collected between 2002 and 2004, the test identified approximately 32% as positive using conventional criteria, though alternative indices suggested even higher detection rates. The practical implication for practitioners is that a negative MAC result provides strong evidence against recent West Nile exposure, whereas positive results reliably indicate infection—though the authors note that test refinements using alternative mathematical indices may further improve detection of marginal cases. For equine professionals managing populations in endemic areas or during outbreak investigations, the IgM capture ELISA represents a dependable point in a diagnostic algorithm, particularly valuable for its high specificity in confirming recent exposure in symptomatic or at-risk horses.
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Practical Takeaways
- •The IgM capture ELISA is a reliable diagnostic test for identifying horses with recent West Nile virus exposure; at standard cutoff a negative result makes active WNV disease unlikely
- •The high specificity (99.2%) means positive results are highly trustworthy and can guide treatment and biosecurity decisions with confidence
- •A negative test does not completely rule out WNV infection in individual cases, so clinical judgment should be used alongside serology, particularly in symptomatic horses
Key Findings
- •MAC ELISA at cutoff point 2.0 achieved 91.7% sensitivity and 99.2% specificity for detecting WN virus IgM antibodies in horses
- •Area under ROC curve of 0.95 (95% CI 0.89–1.0) indicates the MAC is a useful diagnostic tool for recent WN virus exposure
- •Of 602 additional diagnostic samples tested between 2002–2004, 194 horses (32%) were positive using standard cutoff criteria
- •Alternative seropositivity indices developed in the study approached AUC of 1.0 with smaller confidence intervals, potentially improving test performance