As of Nov. 3, cases of equine illness caused this year by West Nile virus (WNV) confirmed at the USDA’s National Veterinary Services Laboratories had risen to 12,843; 12,105 cases more than the final case count for 2001. Vaccinating for WNV and considering horses with signs of neurological disease as potential WNV cases has become an everyday practice for most U.S. veterinarians, although the onset of cold weather and the end of mosquito season has slowed down or curbed the caseload in many areas.

The spread of WNV was inevitable, yet it still caught many by surprise. William Saville, DVM, PhD, Dipl. ACVIM, said, “I don’t think anyone would have dreamed that this would move this far this fast.”

Of the 39 states that have reported the virus in horses, Nebraska had the highest number–1,096 cases. The other states and their cumulative case numbers are listed and updated periodically by the USDA at www.aphis.usda.gov/oa/wnv/wnvstats.html. Nebraska veterinarians are curious as to why their case numbers are so high. The Nebraska Department of Agriculture (NDA) is assisting with a cooperative study between the University of Nebraska’s Veterinary Diagnostic Center and Colorado State University (CSU). Veterinary students from CSU currently are conducting phone interviews with horse owners who had confirmed equine cases this year.

Jim Weiss, DVM, animal epidemiologist for the NDA, said, “When we started getting positive reports, we tried keeping track of (outcomes) ourselves by contacting the veterinarians. When we got up past 100, the positives started coming in fast and furious, so then we just kept track of the amount of positives