Disease

The Colorado Department of Agriculture’s State Veterinarian’s Office is announcing a confirmation of a horse in Adams County positive for both Equine Infectious Anemia (EIA) and Equine Piroplasmosis. The initial positive was identified on December 8 during routine testing for movement, underscoring the necessity of Coggins testing for transport requirements. Confirmatory testing was completed at the USDA’s National Veterinary Services Laboratory (NVSL) on December 23, 2025. 

The Colorado State Veterinarian’s Office is actively monitoring an outbreak of Equine Herpes Virus (EHV-1) in Texas and Oklahoma. EHV-1 is a highly contagious and sometimes fatal virus that can cause a serious neurological disease in horses called Equine Herpes Myeloencephalopathy (EHM). 

This outbreak has been connected to horses that participated in or were around barrel racing and rodeo events in Texas and Oklahoma over the past several weeks. Confirmed cases of EHM have been reported in both states, and the investigation into other sick horses is ongoing.

In an effort to curb further spread of the HPAI virus and implement additional control measures to protect the dairy and poultry industries and public health in Colorado, the Colorado Department of Agriculture is implementing mandatory statewide surveillance for all Colorado Department of Public Health and Environment (CDPHE) licensed commercial cow dairies. This action will help identify any additional infected dairies with the virus with the goal of preventing further spread of the disease.

The Colorado State Veterinarian’s office has confirmed the first case of equine West Nile Virus (WNV) of 2023 in a gelding residing in Weld County. The horse presented with sudden neurological symptoms including weakness, stumbling and recumbency and was euthanized as a result of his condition. The age and vaccine status for this gelding are unknown.  

The U.S. Food and Drug Administration (FDA) and the Colorado Department of Agriculture (CDA) are cautioning horse owners not to feed Top of the Rockies alfalfa cubes with the date codes 111222, 111322, 111422, 111522, and 111622. Consumers who have products marked with those date codes or who are unsure of the date code should throw them away in a secure container and follow the handling and cleaning instructions below.

A horse residing in Weld County has been diagnosed with West Nile Virus (WNV), marking Colorado’s first confirmed equine WNV case in 2021. The horse, which had not been vaccinated against WNV, developed acute neurological signs on July 24, 2021 and is currently recovering.  

The Colorado Departments of Agriculture and Public Health and Environment have confirmed that a mule residing in Eagle County recently tested positive for bat variant rabies.  This is the first case of rabies in domestic livestock in Colorado this year and the first case of rabies in an equine in Colorado since 2013.  

The spillover of bat variant rabies into domestic animals and wildlife is less common than skunk variant rabies in Colorado but is still possible.