The Bureau of Land Management suspects Equine Influenza Virus H3N8, a virus common among wild and domestic horses, has caused the deaths of 94 horses since April 23 at a Cañon City holding facility.

There are more than 2,500 wild horses at the facility, including most of the horses gathered from the famous Sand Wash Basin herd in Moffat County last fall, but the illness is mostly spreading among horses captured from the West Douglas Herd Area, five miles south of Rangely, according to a news release on Thursday, April 28.

The release said polymerase chain reaction (PCR) laboratory test results from two laboratories found the virus in several horses.

A report completed by USDA Animal and Plant Health Inspection Service veterinarian Dr. Albert Kane on Thursday noted that while the pneumonia-like illness has been deadly for the West Douglas horses, symptoms have been mild among other horses at the facility.

Kane’s report also stated that the West Douglas horses were partially vaccinated or unvaccinated, which could be a factor in the spread of the illness. He said the initial illness arose five to 10 days after a group of 50 horses received their first vaccinations and appeared first and most severely in that same group of horses.

The West Douglas horses were captured in early August 2021 and should have been vaccinated shortly thereafter, according to BLM Colorado Spokesperson Steven Hall.

“Part of our review of what happened in this situation, is to determine why these horses hadn’t been vaccinated,” Hall said. “Was there an issue with resources? Was there with a number of horses at the facility? Was there an issue with COVID? We’re trying to determine what the factors were that led to these horses not being vaccinated.”

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The BLM website states that “vaccines for adult horses and burros are administered and boostered as soon as possible after the animals arrive at a corral facility. It is a race against time to build immunity by vaccination while the animals are increasingly exposed to these viruses and bacteria in their new environment. Unfortunately, the respiratory diseases (flu, rhino and strangles) are highly contagious and difficult to control through vaccination alone. The vaccines may help limit how quickly and severely the illness spreads in a group setting.”

Kane’s report also suggested the West Douglas horses could have been compromised by smoke from the Oil Springs Fire, which burned 12,613 acres in the summer of 2021, including much of the herd’s range.

Thursday’s news release said 95 horses have died from the illness, but the death of a foal on April 18 has been deemed unrelated. As of Friday, April 29, Hall said there have been no additional deaths since Thursday.

The American Wild Horse Campaign, which has sharply criticized the deaths, is calling on Colorado Gov. Jared Polis and state and federal policymakers to halt all wild horse roundups until the Cañon City investigation is complete.

“The suspension of roundups is imperative,” the advocacy group said in a news release on Friday, adding that a roundup is scheduled this summer for the Piceance-East Douglas herd outside of Meeker.

The outbreak has also canceled adoption events and prevented Sand Wash Basin horses from being a part of the Meeker Mustang Makeover.