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Colorado State Veterinarian confirms Western Slope Equine West Nile Virus case

Christian Fernsby |
The total number of horses in Colorado with confirmed West Nile Virus (WNV) cases has risen to 21, with a first case of equine WNV confirmed in Mesa County.

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Additional horses in Weld, Larimer, Morgan, and Douglas counties have also tested positive for WNV. Of the confirmed positive cases, five horses have died or have been euthanized.

“The West Nile Virus vaccine has proven to be safe and effective in preventing disease. Horse owners should work with their veterinarians to determine the most appropriate vaccination schedule for their horses. It is important to note WNV is a core vaccine recommended by the American Association of Equine Practitioners,” said Colorado State Veterinarian Dr. Maggie Baldwin.

Mosquito pools from Weld, Larimer, Boulder, Adams, Arapahoe, Delta, Denver, Mesa, and Pueblo counties have tested positive for WNV this summer. There have been fifty eight human cases of WNV in Colorado in 2021 resulting in two human deaths.

Vaccination for WNV is an effective way to protect horses from the virus. 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.

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.

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.

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