First Confirmed Case in 2017 of Equine West Nile Virus (WNV) in Colorado

A horse residing in Larimer County has been diagnosed with West Nile Virus; this is the first confirmed case of WNV in a horse in 2017.  This index case was diagnosed by Colorado State University Veterinary Diagnostic Laboratory in Fort Collins on August 02, 2017.

Vaccines in horses have proven to be a very effective prevention tool.  Horses that have been vaccinated in past years need an annual booster shot.  If an owner did not vaccinate their 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 need 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. 

Neurologic Horses and Reportable Diseases

Any time a horse displays signs consistent with neurologic disease, a complete neurologic examination is warranted.  It is also important to know what samples should be collected and submitted for diagnostic testing when ruling out reportable infectious diseases. 

Unless clinical presentation, epidemiologic links, or exposure is definitive for a non-reportable disease, always consider it to be a reportable disease and notify the State Veterinarian’s Office. 


REPORTABLE diseases in Colorado

to the Colorado Department of Agriculture


Rabies *


Equine Herpes Myeloencephalopathy


EEE/WEE/VEE encephalomyelitidies *

Equine Protozoal Myeloencephalitis

WNV encephalitis *

Equine Degenerative Myeloencephalopathy

Other: any disease of unusual morbidity or mortality that does not fit a normally expected clinical picture.

Cervical Vertebral Stenotic Myelopathy  (Wobblers)

Equine Lower Motor Neuron Disease

Other: abscess, tumor, toxicity, trauma

* indicates diseases also reportable to the Colorado Department of Public Health

Veterinarians need to call the State Veterinarian’s Office at (303)869-9130 to report suggestive signs of the reportable diseases listed above, even if the disease has not been confirmed.  If it is after-hours, our office phone message will indicate which staff veterinarian is on call. 

Sample Collection and Submission:

All samples submitted to a diagnostic laboratory, shall be accompanied by test submission forms with complete information, including:

  • 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 (diagnostic testing for neurologic symptoms for reportable disease, abortion storms (EHV), or vaccination titers)

A staff veterinarian from the Colorado Department of Agriculture will follow-up with the submitting veterinarian and owner, if necessary, on all positive results received for a reportable disease received.  Having the above information allows for swift follow-up and actions required to control the disease.

Keep an eye out for the new reportable disease forms coming soon from the Colorado Department of Agriculture!

While Awaiting 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.  When indicated, State public health or local/regional public health should be notified.  See the following resources:

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

                AAEP Suspected Case of Infectious Neurologic Disease