Since the outbreak began on April 23, veterinarians have confirmed pneumonia caused by H3 equine influenza virus, complicated by bacterial coinfection, based on culture and microscopic examination of samples obtained at necropsy. On May 5 lab testing identified Streptococcus equi subspecies zooepidemicus (aka strep zoo) and Actinobacillus bacteria in deceased horses’ lung tissues. These findings indicate the disease and deaths at the facility likely resulted from “a multifactorial respiratory disease complex that includes the equine influenza virus, bacterial pathogens that are common in the environment and among all types of horses, as well as environmental and host specific cofactors and comorbidities,” the BLM said in its situation report.

On May 6 the BLM announced the formation of an ongoing collaboration to investigate the factors contributing to the outbreak. The cooperative effort includes veterinarians and scientists from the U.S. and Colorado Departments of Agriculture, Colorado State University’s Veterinary Diagnostic Laboratory, the University of California, Davis’, Equine Infectious Disease Research Laboratory, and the University of Kentucky’s Gluck Equine Research Center.

The Equine Disease Communication Center released this information on May 6, 2022.

About Equine Influenza

Equine influenza is a highly contagious respiratory disease that infects horses, ponies, and other equids, such as donkeys, mules, and zebras. The virus that causes it is spread via saliva and respiratory secretions from infected horses. Horses are commonly exposed via horse-to-horse contact; aerosol transmission from coughing and sneezing; and contact with humans’ contaminated hands, shoes, or clothes or contaminated tack, buckets, or other equipment.

Clinical signs of equine influenza infection can include a high fever (up to 106°F); a dry, hacking cough; depression; weakness; anorexia; serous (watery) nasal discharge; and slightly enlarged lymph nodes. Consider monitoring your horse’s health at shows by taking his temperature daily, which can help you pick up on signs of infection early and take appropriate measures to reduce disease spread.

​Vaccination is an important and inexpensive way to protect your horse. US Equestrian requires proof that horses have had an equine influenza vaccination within the six months prior to attending organization-sanctioned competitions or events. Your veterinarian can help you determine what other vaccines your horse might benefit from.

In addition to vaccinating, following strict biosecurity protocols can help reduce your horse’s chance of infection and disease. Such measures include quarantining new equine arrivals at barns, disinfecting buckets and equipment, and preventing nose-to-nose contact between horses.