Colorado reports two equine West Nile virus cases

The Colorado State Veterinarian’s Office has reported two cases of West Nile virus (WNV) in horses across Pueblo and Montrose counties.

In Pueblo County, a 2-year-old Quarter Horse mare was confirmed positive on September 9 after exhibiting symptoms including anorexia, abnormal mentation, and ataxia. In Montrose County, an unvaccinated 4-year-old Quarter Horse gelding tested positive after showing signs of muscle twitching, teeth grinding, weakness, and ataxia. Both horses are currently alive.

West Nile virus is transmitted to horses through mosquito bites. While there is no cure, some animals may recover with supportive care. Mortality rates for equine WNV can reach between 30% and 40%. Health officials note that vaccination is an effective prevention tool, though horses may require annual boosters depending on the length of the local mosquito season.