From the Colorado State Veterinarian’s Office:

Five equine cases of West Nile virus (WNV) have been diagnosed in Colorado as of Aug. 14. The WNV positive horses are from Fremont, Weld, Montrose (2), and Larimer counties.

The incidence of the disease varies from year to year and depends on a number of factors, including mosquito numbers. WNV 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.

Infected horses can display clinical signs 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