Equine Influenza virus likely to blame in mortality in feral horses at BLM facility
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 mortality that is occurring at the Bureau of Land Management’s Wild Horse and Burro Corrals located on the Colorado Department of Corrections (CDOC) East Canon Complex in Canon City, Colo. 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.
This strain of equine influenza (subtype H3N8) 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.
The PCR testing has also identified two equine herpes viruses (EHV-2 and EHV-5) but these commonly occur in normal, healthy horses, and it is unclear to what extent these may also be contributing to the severity of the clinical signs observed in the more severely affected group of horses at the facility.
More typical mild clinical signs of influenza are also being observed in approximately 10-20 percent of the other 2,184 horses at the facility that are not from West Douglas. No mortality has occurred in the larger groups of horses. The West Douglas horses were gathered in an emergency operation in 2021 following a wildfire that impacted their habitat. As of today, April 28, 95 horses have died at the facility since April 23.
“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.”
MITIGATING THE SPREAD
“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 U.S. 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 at this time and for the foreseeable future until it has been determined that the animals are again healthy and pose no risk to the domestic equine population in the community.
According to a report prepared by USDA APHIS veterinarian Albert Kane, initial clinical signs included horses found dead in pens of West Douglas horses — thought to include respiratory and neurologic signs, after the first couple days clinical signs thought to be neurologic were attributed to hypoxia due to severe respiratory compromise, attending veterinarian concluded no neurologic signs were present — nasal discharge and coughing observed in the severely affected “West Douglas” pens and after a few days in other pens throughout the facility.
According to the report, horses found dead in pens presented with a pneumonia characterized by “severe acute pulmonary edema and mild hemorrhage” or a respiratory condition characterized by mild/moderate fever, coughing or nasal discharge, depression, and labored breathing.
To date, according to the veterinary report, approximately 15 necropsies have been conducted with associated tissues from these and several still living horses submitted for viral PCR testing, histopathology, bacterial culture and virus isolation as well as testing for specific EHV subtypes and a broad panel of respiratory viruses including, influenza, rhinitis virus, and strep species. No additional carcasses will be sent for necropsy, but there may be on site necropsies if indicated.
The West Douglas horses, according to the report, are either partially vaccinated or unvaccinated — this problem appeared to start shortly (5 five to 10 days) after an initial group of about 50 of these horses received their first vaccinations and appeared initially to start in and be most severe in this same group of horses. The West Douglas horses were gathered and removed from the range after a large wildfire drove them into surrounding areas to escape. Kane noted particularly high winds in the days prior to the outbreak, producing severely dusty conditions with blowing dirt heavy enough in areas to block visibility for short intervals of time. He noted that the most affected horses and other horses throughout the facility are almost universally in good body condition.
Colorado State Veterinarian Dr. Maggie Baldwin issued the following statement on the Cañon City Wild Horse and Burro Facility disease outbreak.
“The Colorado State Veterinarian’s Office was notified on April 23 about the disease outbreak that has resulted in the death of 85 horses at the Cañon City Wild Horse and Burro Facility. The Bureau of Land Management and the U.S. Department of Agriculture are actively investigating the incident and monitoring the wellbeing of animals at the facility. CDA is working with the two agencies to support their response to this incident.
On Tuesday, April 26, a field veterinarian with CDA conducted a site visit to the Cañon City facility and reviewed biosecurity measures being implemented at the facility. BLM has put a voluntary quarantine in place and has instituted rigorous measures to prevent further spread of the disease. Affected horses have been segregated and quarantined from the rest of the herd.
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