West Nile is transmitted to horses via bites from infected mosquitoes. | Photo: iStock

A 2-year-old Quarter Horse filly from Owyhee County has tested positive for West Nile virus, the Equine Disease Communication Center (EDCC) reported July 27.

“The horse showed an onset of clinical signs on July 19 … including ataxia and incoordination,” the EDCC said. “Testing was confirmed positive for WNV at the (Idaho State Department of Agriculture) Animal Health Laboratory. The horse had been vaccinated as a filly but had not received a booster vaccination. The horse is improving with supportive care.”

West Nile is transmitted to horses via bites from infected mosquitoes. Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculation; hyperesthesia (hypersensitivity to touch and sound); changes in mentation (mentality), when horses look like they are daydreaming or “just not with it”; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and “spinal” signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia. There are no specific treatments for WNV, however supportive care can help horses recover in some cases. Equine mortality rate can be as high as 30-40%