Frequently Asked Questions (FAQ) about Equine Influenza

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The following Frequently Asked Questions about Equine Influenza were prepared by the Colorado State Veterinarian's Office. You can download a PDF of the questions and answers here

What virus is causing the disease outbreak at the BLM facility located on the Colorado Department of Corrections East Cañon Complex in Cañon City?
The strain of equine influenza identified as the likely cause of the respiratory disease outbreak and associated mortality at the BLM facility in Cañon City was categorized as subtype H3N8 by two leading veterinary diagnostic laboratories in the United States. The diagnostic tests identified the virus in nasal swabs and lung tissue from several horses.

Equine influenza FAQ

What is the H3N8 strain of equine influenza?
Equine influenza is a highly contagious respiratory disease with a high rate of transmission among horses and a short incubation time (1-3 days). It is spread through aerosols from coughing infected horses as well as through contact with contaminated materials, such as clothing or surfaces. This specific strain is common among both wild and domestic horses in the United States and across the world. 

What does this detection of equine flu mean for horse owners in Colorado?
Animal health experts believe this outbreak is confined to the Cañon City facility and does not pose a risk to the general equine population in Colorado. The affected horses are segregated and under voluntary quarantine at the facility. The Bureau of Land Management has instituted rigorous measures to prevent further spread of the disease and has been working with the State Veterinarian’s Office, the Colorado Department of Corrections, as well as the US Department of Agriculture on the investigation and response to the outbreak. 

What’s next for the horses at the Cañon City Facility?
The Bureau of Land Management 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 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.

Is this virus related to Highly Pathogenic Avian Influenza?
No, the H3N8 strain is not related to the current outbreak of highly pathogenic avian influenza, or HPAI, which is categorized as subtype H5N1. The HPAI strain is currently impacting wild birds and poultry across the United States, including Colorado. More information about avian influenza can be found at

What are the symptoms of equine influenza?
Symptoms in horses can include high fever (up to 106°F), nasal discharge, swollen lymph nodes, and a dry, harsh cough. Depression, weakness, and decreased feed consumption are frequently seen. Symptoms usually last less than three days in uncomplicated cases. Mildly affected horses typically recover uneventfully in 2-3 weeks. Equine influenza typically does not result in high mortality of horses, but many factors can play a role in the severity of disease in individual horses and within a herd. 

How is equine influenza transmitted?
Equine influenza can be spread through direct contact with infected horses or airborne through coughing from infected horses. The virus can also be transmitted by contaminated clothing, equipment, and tack. Some horses may not show outward signs of infection, but can shed the virus and infect susceptible horses. 

Is there treatment for equine influenza?
Treatment generally consists of rest and supportive care for horses affected by the virus. More severely affected horses can also be given treatment by their veterinarian to reduce inflammation and fever. 

How can equine influenza be prevented?
Proper vaccination and biocontrol measures are the best available defenses against equine influenza. An equine influenza vaccine is available. Horse owners should work with their veterinarians to determine the best vaccine schedule for their horses.

What should I do if my horse gets sick?
If you are a horse owner whose horse shows symptoms similar to equine influenza, contact your veterinarian. While equine influenza is not a reportable disease in the state of Colorado, the State Veterinarian’s Office continues to support veterinarians across the state as they work within their communities to identify any potential cases. 

What do the numbers H3N8 mean?
Strains of influenza A virus are named with Hs and Ns. H stands for hemagglutinin and N for neuraminidase. Both are proteins on the surface of the virus (antigens) that help it invade cells. There are 18 different H subtypes and 11 N subtypes, resulting in 198 possible combinations. Sometimes the strains trade genetic information, taking on new characteristics that our immune systems have never seen. This can lead to severe illness, and even death.


Questions added 5/2/22

Which horses at the CDOC East Cañon Complex were affected?
Reported mortalities were in horses from the West Douglas range in western Colorado, near the border with Utah. Approximately 450 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 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. Information on the West Douglas gather can be found online at 2021 West Douglas Herd Area Emergency Wild Horse Gather | Bureau of Land Management (

What was the vaccination status of the affected horses?
The administration of vaccines to the wild horses and burros removed from public lands has been a long-standing practice within the Wild Horse and Burro program. The West Douglas horses had been in the facility for about 9 months but are still unsettled, flighty as a group, and easily disturbed in the pens. Most of the facility population is current (within 6 months) for flu/rhino vaccination, however the West Douglas horses are either unvaccinated, have only received one shot, or only recently received their booster shots about 10 days before the outbreak. BLM is reviewing the vaccination schedule for these horses as well as working with a team of experts to determine what impact vaccinations may or may not have contributed. 

The remainder of the horses at the Cañon City facility are vaccinated. Approximately 10%-20% of vaccinated horses in other areas of the facility are experiencing mild symptoms and no mortalities.  

What about the herpes viruses discovered in the samples?
Two equine herpes viruses (EHV-2 and EHV-5) were also identified in the samples tested by the veterinary diagnostic laboratories. Both of these strains commonly occur in normal, healthy horses, and it is unclear to what extent they may be contributing to the severity of the clinical signs observed in affected horses. Onsite veterinarians are working with diagnostic laboratories to determine the best course of action for further investigation of these viruses.
EHV-2 and EHV-5 are classified as gamma-herpesviruses, which generally cause milder infection than alpha-herpesviruses, and often present as asymptomatic. Both strains are shown to be prevalent among the general horse population and can be identified in animals with and without disease, making it difficult to assess their impact on other infections. The more common viruses type EHV-1 and EHV-4 were not detected by the diagnostic laboratory. 
EHV-2 does not usually cause disease on its own but is believed to cause suppression of the horse's immunity to other viral infections and allows them to cause signs of disease, usually respiratory infection, i.e., elevated temperature, watery nasal discharge, enlarged glands under the jaw and coughing. In studies, EHV-5 has not been associated with signs of poor performance or respiratory disease.

What about other animals at the complex, such as dogs in training or the water buffalo at the Four Mile dairy? 
State animal health experts believe this outbreak is confined to the affected horses at the Cañon City facility and the infection does not pose a risk to other animals on or near the premises. The virus poses a low risk for spread to the other animals on the premises with the biosecurity measures that have been implemented. 

What about the safety of companion animals of the staff who work on the complex?
Staff working at the facility and dealing with the outbreak of the disease are asked to follow strict biosecurity measures, including changing out of their clothes when leaving the facility to limit the spread of the virus off the premises.  


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