Two Colorado horses infected with West Nile Virus

One horse in Weld County and another in Fremont County have been diagnosed with West Nile virus. As of July 18 these were the only diagnosed equine cases of West Nile in Colorado. Both horses are being treated for symptoms of the illness.

West Nile virus is a disease that threatens the health of humans, horses and other animals. “Late summer and early fall have traditionally been the time of year when we are most likely to see WNV cases reported in horse,” said Colorado State Veterinarian, Dr. Keith Roehr. “In the past few years there have been very few reported equine case of WNV in Colorado; it is difficult to project how many WNV cases we may see in the coming months.”

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The transmission of the disease varies from year to year and depends on a number of factors, including mosquito numbers. The West Nile virus can be carried by infected birds and then spread to mosquitoes that bite those birds.The mosquitoes can then pass the virus to humans and animals.

Infected horses may display symptoms including head tilt, muscle tremors, stumbling, lack of coordination, weakness of the limbs or partial paralysis.If horses exhibit clinical signs consistent with WNV, it is very important for horse owners to contact their veterinarian in order to confirm the diagnosis through laboratory testing. Horse owners should consult their veterinarian to determine an appropriate prevention strategy for their horses.

Vaccines have proven to be a very effective prevention tool. Horses that have been vaccinated in past years will need an annual booster shot. However, if an owner did not vaccinate their animal in previous years, the horse will need the two-shot vaccination series within a three to six week period. There is no West Nile virus vaccine approved for humans.

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.

For complete and updated information concerning new WNV equine case information including numbers and location of test positive horses visit .