Lab tests confirmed that a previously “unknown, highly contagious” disease, which killed nearly 100 wild horses in a state run facility in Canon 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 states 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 Canon City facility to prevent future outbreaks like this from occurring,” said BLM Colorado Acting Associate State Director Ben Gruber.

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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