Since the index case of the equine West Nile Virus (WNV) was identified in Colorado on July 30, 2021, horses from multiple Colorado counties have tested positive for WNV. Four additional horses in Weld County, three horses in Adams County, two horses in Boulder County and one horse each in Elbert, Otero, Morgan, and Fremont counties have tested positive for WNV. This brings the total test positive cases in 2021 to fourteen.
“With more than a dozen horses testing positive for West Nile Virus this year, it’s important to remember that vaccinations are critical to protect the health of Colorado horses,” said State Veterinarian Dr. Maggie Baldwin. “In addition to vaccines, horse owners should work to reduce mosquito populations on their premises. West Nile Virus is spread by mosquitoes and mitigating that vector helps to reduce the risk of disease to both horses and people.”
Mosquito pools from Weld, Larimer, Boulder, Adams, Arapahoe, Delta, Denver, and Pueblo counties have tested positive for WNV this summer and the Colorado Department of Public Health and Environment has recorded twenty nine human cases of WNV this year. CDPHE publishes data on human West Nile cases and positive mosquito pools on the CDPHE WNV website.
Vaccination for WNV is one of the core vaccines recommended for livestock by the American Association of Equine Practitioners (AAEP). If a horse has not been vaccinated in previous years, it will need the two-shot vaccination series. Horses need an annual booster to protect against WNV. Visit the AAEP website for a comprehensive list of vaccination recommendations. Horse owners should work with their veterinarians to determine the best vaccine schedule for their horses.
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.
WNV is a viral disease that cycles between wild birds and mosquitoes, and can sometimes affect other species, like people and horses, as dead-end hosts. Clinical cases in horses are typically characterized by anorexia, depression, and neurological signs, which may include ataxia, 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 | Department of Public Health & Environment.