More information about West Nile virus (WNV), its symptoms, and its clinical outcome is available as the result of a telephone survey that was conducted in Colorado and Nebraska. Interviewed were the owners of 493 horses that developed West Nile virus between Sept. 1 and Dec. 31, 2002. Colorado State University released the study's data and conclusions on March 25.
Based on the survey, the most common clinical signs associated with WNV included ataxia (a staggering, or drunk-like gait, 73%), weakness (69%), lethargy or depression (61%), and muscle twitching, especially on the face and in the forequarters (60%). Weakness was often more severe in the hind limbs.
The most commonly used treatments were flunixin meglumine (Banamine 73%), dimethylsulfoxide (DMSO, 52%), oral or intravenous fluids (39%), phenylbutazone (Bute, 22%), and vitamins (12%). Twelve horses (3%) were treated by using a supporting sling to assist in managing recumbancy.
The survival status was available for 482 of the horses, and of that group, 71.4% were still alive at the time of the survey. The remaining 28.6% died or were euthanized, which is similar to reports from other regions of the United States. Of the surviving animals, 82% were considered to be fully recovered by their owners.
Older horses that developed WNV were more likely to die as were horses that could not stand up.
Vaccinated horses were less likely to die or be euthanized. Only 13 of the horses in the study had been vaccinated according to recommendations. Twelve survived and the status of the other was not known.
The survey was a collaborative effort between the state veterinarians in Colorado and Nebraska, the Veterinary Diagnostic Center in Nebraska, and Colorado State University's College of Veterinary Medicine and Biomedical Sciences.