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Horse owners urged to take precautions regarding West Nile Virus

Eight equine cases of West Nile Virus (WNV) have been diagnosed in Colorado as of Aug. 22.

The WNV positive horses are from Fremont, Weld (three cases), Delta, Montrose, Mesa and Larimer counties.

The incidence 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 locally by mosquitoes that bite those birds. The mosquitoes can then pass the virus to humans and animals. Horses are a dead-end host and therefore infected horses pose no threat to public health, but they can be severely affected and are an indicator of the presence of the virus in mosquito populations.

Horse owners are encouraged to:

1. Contact their veterinarian if horses exhibit clinical signs consistent with WNV so that a proper diagnosis can be obtained.

2. Work with their veterinarian to determine an appropriate prevention strategy.

3. Mitigate the mosquito populations and possible mosquito breeding areas on your property.

4. Take precautions to develop methods to repel mosquitos from biting your horse.

5. Vaccinate your horses for WNV, as it is a very effective prevention tool.

Our veterinary staff at the State Veterinarian’s Office has done a very limited and informal survey of WNV vaccine sales in Colorado; it indicates a significant drop in vaccine sales over the past years. If this small survey is indicative of the overall sales, it is a disturbing trend. Of the eight horses that have been WNV-positive, we have not been able to confirm that any of the horses have been vaccinated for WNV.

For more information concerning WNV and Colorado counties that have confirmed test-positive horses, visit the following sites:<>,,

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