Colorado confirms first 2020 case of equine West Nile Virus

Colorado confirms first 2020 case of equine West Nile Virus

The following was distributed to Colorado veterinarians by the Colorado State Veterinarian’s Office on September 30, 2020. Click here to sign up to receive immediate updates from the Colorado State Veterinarian’s Office.

A horse residing in Jefferson County has been diagnosed with West Nile Virus; this is Colorado’s first confirmed equine WNV case in 2020.

Vaccines in horses have proven to be a very effective prevention tool for West Nile Virus. Horses that have been vaccinated in past years need an annual booster. If an owner did not vaccinate the animal in previous years, the horse will need the two-shot vaccination series within a three to four week period.

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

Information for veterinarians

All cases of acute equine neurologic disease must be reported to our office immediately, unless the cause is known toxicity or trauma. Call the State Veterinarian’s Office office at 303-869-9130 to report suggestive signs of reportable diseases, even if the disease has not been confirmed. If it is after-hours, the office phone message will indicate which staff veterinarian is on call.

Visit the state’s Reportable Disease Page for more information on reportable diseases and how to use our online reporting tool. Here’s a direct link to the Equine Neurologic Disease webpage for more information on the reportable equine neurologic diseases, clinical signs, testing, and additional resources.

It is important that the State Veterinarian’s Office receive the following information:

  • Veterinarian contact information
  • Owner contact and premises information
  • Animal information, including identification (microchip number, tattoo, or brand)
  • Physical location of the animal (if different than the owner’s address)
  • Purpose of testing (i.e., diagnostic testing vs. vaccination titers)
  • Clinical history and vaccination history

While awaiting test results, neurologic horses should be isolated and biosecurity measures shall be put in place, due to the potential for disease transmission. Some neurologic diseases in horses are zoonotic, so precautions should be taken for veterinarians, owners, and anyone else interacting with the horse while waiting for results. See the following resources:

NASPHV Compendium of Veterinary Standard Precautions for Zoonotic Disease Prevention (2015) 

AAEP Guidelines: Suspected Case of Infectious Neurologic Disease


Public health

The Colorado Department of Public Health and Environment has reported 20 human WNV cases in 2020 so far. CDPHE publishes data on human West Nile cases, as well as positive mosquito pools, on the CDPHE WNV website.

CDA Equine Neurologic Disease
CDPHE West Nile Virus