An outbreak of equine influenza has claimed the lives of 119 Mustangs at a Bureau of Land Management (BLM) facility in Colorado.
The affected horses belong to a group originally gathered late last summer from the West Douglas Herd Area in the northwestern part of the state. According to a May 2 situation report filed by BLM officials, nine horses from that group—now held at the Cañon City Wild Horse and Burro Facility, in Fremont County—were found dead on the same day in late April. Several more horses were gravely ill with what was initially thought to be neurologic signs but later attributed to hypoxia (lack of oxygen) from severe pneumonia.
Over the following days, dozens more horses died or were euthanized for “severe debilitating respiratory distress.” Post mortem examinations consistently revealed pneumonia characterized by severe pulmonary edema and hemorrhage. Signs of illness, including fever, nasal discharge and coughing were seen in an additional 40 to 60 percent of the West Douglas horses.
Polymerase chain reaction (PCR) testing of blood, nasal swabs and other tissue confirmed the cause of illness in the herd was H3N8 strain of equine influenza. Subsequent testing has shown the virus is the Florida Clad 1 sublineage—an endemic strain of equine influenza in North America. Diagnostic tests ruled out both the respiratory and neurologic form of equine herpesvirus.
The May 2 report also notes possible contributing factors to the outbreak, including severe wind and dust storms and a low vaccination rate: While most of the horses at the facility are up-to-date on vaccines, the West Douglas horses in the affected pens were either unvaccinated, had only received one shot or had only recently received a booster.
The BLM facility remains under quarantine with biosecurity and dust-mitigation measures in place. Veterinary officials are providing supportive care, including anti-inflammatory and antibiotic medications, for horses who can be handled without causing stress that might exacerbate underlying issues or increase the risk injury.
