Colorado State Veterinarian Confirms Equine West Nile Virus Case in Weld County

August 11, 2022

A three year old gelding residing in Weld County has been diagnosed with West Nile Virus (WNV) and is now recovering. The horse developed neurological symptoms in late July, including weakness, stumbling and poor muscle control. The gelding’s vaccine status is unknown. This is Colorado’s first confirmed equine WNV case in 2022.

The first human case of WNV this year was confirmed in Delta County on July 29, 2022 with four additional human cases confirmed, one in Montrose County, Arapahoe County, an additional case in Delta County and one in Boulder County. Mosquito pools in Adams, Boulder, Larimer, Mesa, and Weld counties have tested positive for WNV this summer.

“West Nile Virus is actively circulating in Colorado and continues to pose a risk to people and unvaccinated equines,” said Colorado State Veterinarian Dr. Maggie Baldwin. “Vaccines are an effective prevention tool for West Nile Virus in horses and owners should work with their veterinarians to determine the appropriate vaccination schedule for their horses.”

WNV is a viral disease that cycles between wild birds and mosquitoes, and can sometimes affect other species like people and equines (as dead end hosts, meaning they cannot pass the virus on further). Clinical cases in horses can include weight loss, depression, muscle weakness or paralysis of one or more limbs, teeth grinding, aimless wandering, convulsions and/or circling. For information on human WNV symptoms and prevention see West Nile virus and your health from the Department of Public Health & Environment.

West Nile Virus is one of the AAEP core vaccinations for horses. Horses vaccinated for WNV in past years will need an annual booster. If a horse has not been vaccinated in previous years, it will need the two-shot vaccination series. Visit the AAEP website for a comprehensive list of vaccination recommendations.  

In addition to vaccinations, horse owners should also work diligently to reduce mosquito populations and their possible breeding areas where horses are located. Recommendations include removing stagnant water sources, using mosquito repellents, and keeping animals inside during the bugs’ feeding times, typically early in the morning and evening.  

Any time a horse displays clinical signs consistent with neurologic disease, a complete veterinary examination is warranted. All infectious or contagious equine neurologic diseases are reportable to the Colorado State Veterinarian's Office at (303) 869-9130. A chart of reportable animal diseases in Colorado can be found on the CDA website.

Source: Colorado Department of Agriculture