Animal health authorities in North Dakota have confirmed a case of West Nile virus (WNV) in a Burleigh County mule. According to the Equine Disease Communication Center, the mule was euthanized due to neurologic clinical signs of the disease. The mule was not vaccinated against WNV.

West Nile virus is transmitted to horses via bites from infected mosquitoes. Infected horses show flulike clinical signs, where the horse seems mildly anorexic and depressed. Other clinical signs include coarse muscle and skin fasciculations (twitching); hyperesthesia (hypersensitivity to touch and sound); changes in mentation (mentality), when horses look like they are daydreaming or confused; occasional drowsiness; propulsive walking (driving or pushing forward, often without control); and “spinal” signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia. Equine mortality rate can be as high as 30-40%.

The clinical signs of WNV can be consistent with other neurologic diseases such as equine encephalitis, rabies, and equine herpesvirus; therefore it is important to work with your veterinarian to get an accurate diagnosis through laboratory testing.