A horse residing in Larimer County, Colorado, has been diagnosed with West Nile virus (WNV), the state Department of Agriculture reported Aug. 9. This is the state’s first confirmed case of WNV in a horse in 2017.

This index case was confirmed by the Colorado State University Veterinary Diagnostic Laboratory in Fort Collins on Aug. 2.

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. Equine mortality rate can be as high as 30-40%.

“Strict insect control is an important factor to inhibit the transmission of West Nile virus,” said State Veterinarian Keith Roehr, DVM. “I encourage livestock owners to keep an eye out for standing water for mosquito populations