Horse owners should have equine survivors of West Nile virus (WNV) re-examined by their veterinarians before putting the animals back into work. In a study of Minnesota horses which survived clinical WNV infection, 40% showed WNV residual effects at six months after diagnosis; these neurologic effects can make the horse more dangerous to ride or drive. Julia Wilson, DVM, Dipl. ACVIM, is an associate professor in clinical and population sciences at the University of Minnesota’s (UM) College of Veterinary Medicine. She presented results from this study examining residual effects of WNV to better characterize prognosis at the 2003 Ameri-can Association of Equine Practitioners Convention.

Her research group collaborated with Minnesota’s Department of Health and Board of Animal Health to obtain data on surviving horses with confirmed WNV. Two hundred owners of horses treated for WNV were sent questionnaires in early 2003 and were asked to describe the horse’s use pre- and post-infection, its current neurologic status, length of recovery, observations of relapse or recurrence of clinical signs, to check off any of 11 listed abnormalities that were currently observable, and to comment on any additional concerns.

Of the 200 mailed, 131 questionnaires were returned. Six were discarded because the horses had died or had been euthanized during acute illness. The animals included in the survey were predominantly pleasure horses, followed by breeding animals.

In the group of 125 horses, 102 (81.6%) were considered by the owner to have fully recovered; 13 had been re-evaluated by a veterinarian. Even though the owners believed the horse had fully recovered, only 74 horses (59%) had no observable neurologic or behavioral abnormalities (and thus were considered fully recovered), while the others were considered fully recovered with deficits