By the 2003 West Nile virus (WNV) season, a majority of state laboratories had obtained (or were establishing) the capacity to run the IgM Capture ELISA, the most common quick test for the disease. The test measures a class of antibody produced early after infection, can be performed on serum samples drawn from suspect cases, and takes two to three days to process. Other tests take four days to two weeks, and some are available only on post-mortem samples of brain or spinal cord.

The IgM ELISA was available at the USDA’s National Veterinary Services Laboratories (NVSL) in Ames, Iowa, in 2000. Eileen Ostlund, DVM, PhD, head of the Equine and Ovine Viruses Section of the Diagnostic Virology Laboratory at NVSL, said, “The major expansion coincided with commercial availability of some of the reagents required for the test. This (test) is good evidence that the horse was recently exposed; it’s a very useful test in the live horse.” NVSL receives samples from individual veterinarians and state agriculture or public health officials for testing, if they don’t already have their own in-state quick testing.

“The rapid serum test detects immunoglobulin-M that binds to West Nile virus protein, evidence of an infection,” said Stephen A. Kania, PhD, an assistant professor of Comparative Medicine at the University of Tennessee’s College of Veterinary Medicine, where the test also is performed. “Clinicians and pathologists need to know if they are dealing with a zoonotic infection and need to know what precautions to take.”

“In horses exhibiting neurological signs, there has been a good correlation between positive test results with the rapid serum test and active West Nile virus infection,” said Ronald B. Wilson, DVM, Dipl. ACVP, Tennessee’s state veterinarian and diagnostic laboratory director of the C.E. Kord Animal Disease Laboratory of the Tennessee Department of Agriculture in Nashville