Lab tests confirmed that a previously “unknown, highly contagious” disease, which has killed more than 100 wild horses in a state-run facility in Cañon City, is equine influenza virus, the Bureau of Land Management announced Friday.

The disease, not uncommon to wild and domestic horses, caused a respiratory disease outbreak mostly among the Wild Horse and Burro Facility’s West Douglas horses, which were rounded up near the Colorado’s northwestern border after wildfires impacted their habitat in 2021, the agency said.

Some 10%-20% of the facility’s horse population are showing signs of milder influenza, but they are not horses from West Douglas, the agency said.

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Testing also revealed some of the horses contracted equine herpes viruses that commonly appear in healthy horses. The agency was unsure to what extent the herpes viruses could also be playing a role in the severity of the horses’ sickness, the agency said.

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“The Bureau of Land Management will review operations at the Cañon City facility to prevent future outbreaks like this from occurring,” said BLM Colorado Acting Associate State Director Ben Gruber.

Officials with the Colorado Department of Agriculture said that in addition to an investigation into the incident by the BLM and the U.S. Department of Agriculture, a field veterinarian visited the facility Tuesday and reviewed the biosecurity measures in place. 

BLM is also issuing a voluntary quarantine of the site and has segregated affected horses from the rest of the herd, officials said. BLM is working with officials at the state and federal levels to determine what caused the outbreak. Samples from the facility have been sent to equine diagnostic laboratories for testing. 

Reports suggest that the horses vaccine status may be a common factor in the deaths. 

According to the BLM April 29 situation report, the West Douglas horses in pens 40-43 were either unvaccinated, partially vaccinated or received their booster just 10 days before the outbreak. A mortality table on the situation report shows that all of the 102 horses that have died since the 23rd were in pens 40-43. 

Suzanne Roy, executive director with the American Wild Horse Campaign, said that BLM did not properly execute its duties. 

“Outbreaks of contagious diseases and infections are the direct result of the BLM’s inhumane mass roundups, as once formerly wild horses are confined with thousands of others in holding pens,” Roy said in a release. “Taking horses out of the wild and into a domestic environment requires vaccinations; it appears that the BLM fell short in its care of and responsibility for these federally protected animals.”

BLM spokesman Steven Hall said that the organization is reviewing to see how this incident happened. He added that standard procedure is that wild horses be vaccinated when they are removed from the wild but that the timeline can vary.

He noted that the West Douglas area is unsuitable for wild horses, as water is scarce and the best places for foraging are on private property. He said the horses were collected in a emergency gathering after the wildfires. 

The facility is home to 2,550 horses and will continue to be under voluntary quarantine with no horses allowed to leave the premises for the foreseeable future, the agency said.

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