Equine Influenza Outbreak Cause of Colorado Wild Horse Deaths

Equine influenza has been identified as the cause of 95 wild horse deaths at the Canon City, Colorado, BLM holding facility.

Editor’s Note: The following report was taken from multiple BLM press releases and alerts.

An equine influenza virus that is not uncommon among both wild and domestic horses has been identified as the likely cause of the respiratory disease outbreak and associated death of 95 horses at the BLM’s Wild Horse and Burro Corrals located on the Colorado Department of Corrections (CDOC) East Canon Complex in Canon City. Positive polymerase chain reaction (PCR) laboratory test results from two leading veterinary diagnostic laboratories in the United States identified the virus in nasal swabs and lung tissue from several horses.

The outbreak began on April 23. An independent veterinarian and a federal veterinarian are on-site to help diagnose and treat animals. Horses showing signs of contagious illness are quarantined from the population. 

The BLM release noted that the strain of equine influenza (subtype H3N8) at the Canon City Complex is not related to the current outbreak of highly pathogenic avian influenza (subtype H5N1) that is currently impacting wild birds and poultry across the United States.

PCR testing also identified two types of equine herpesvirus (EHV-2 and EHV-5), but these commonly occur in normal, healthy horses. The BLM noted that it is unclear to what extent these infections might be contributing to the severity of the influenza clinical signs observed in the more severely affected group of horses at the facility.

Horses gathered from the West Douglas area in fall 2021 are the most impacted. The West Douglas horses were gathered in an emergency operation in 2021 following a wildfire that impacted their habitat.

More typical mild clinical signs of influenza are being observed in approximately 10-20 percent of the other 2,184 horses at the facility that are not from West Douglas.

“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. “This tragic outcome was influenced by a population of horses that may have been particularly vulnerable given their time in the West Douglas area and their exposure to last year’s wildfire that prompted their emergency gather.”

“This unfortunate event is being taken very seriously by the Department of Corrections and the BLM,” said CDOC Executive Director Dean Williams. “We are working in coordination to mitigate the spread of the virus and identify and prevent any potential risk which could lead to future similar events.”

BLM continues to work with the attending veterinarians on scene as well as the diagnostic laboratories, veterinarians and epidemiologists from the US Department of Agriculture and the Colorado State Veterinarian’s Office to investigate and mitigate the factors that may be contributing to the most severe cases and prevent further spread of the disease. The facility remains under a voluntary quarantine with no horses allowed to leave the premises until it has been determined that the animals are again healthy and pose no risk to the domestic equine population in the community.

The preliminary veterinarian outbreak report can be found here and additional information can be found online at https://www.blm.gov/programs/wild-horse-and-burro/herd-management/herd-management-areas/colorado.

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