The Equine Disease Communication Center (EDCC) provided an update on the equine influenza outbreak at a Bureau of Land Management (BLM) wild horse holding facility near Canon City, Colorado.
As of May 3, a total of 123 horses have died due to an outbreak of equine influenza. On May 2, the BLM reported that testing of the samples have determined the virus to be the Florida Clade 1 sublineage, an endemic strain in North America.
Timeline of the Outbreak
According to a BLM timeline of this outbreak and from EDCC notes, here is how events played out.
On April 18, a foal that died was submitted for necropsy with concerns for equine herpesvirus (EHV-1). Initial laboratory reports were unremarkable and viral testing was pending
On April 23, 9 horses were found dead in pens 40-43, mostly among the studs that had recently been vaccinated with a 6-way vaccine. Those pens contained horses gathered from the West Douglas Herd Area in July/August of 2021. Several horses were gravely ill showing signs initially thought to be neurologic but later attributed to hypoxia from severe pneumonia. Several horses were taken to the diagnostic laboratory for necropsy. A voluntary quarantine was established with no movement of animals allowed off the premises. Biosecurity measures were increased throughout the facility.
During April 24-25, 46 horses died or were euthanized among the West Douglas horses for severe debilitating respiratory distress. Post mortem examinations consistently found pneumonia characterized by severe pulmonary edema and hemorrhage. Morbidity characterized by respiratory signs including fever, nasal discharge and coughing were also noted in 40-60% of the West Douglas horses.
On April 25, the BLM noted the first increases of respiratory morbidity in other pens, amounting to about 20% noted in other pens throughout the facility.
On April 25, the first samples tested were negative for EHV-1. PCR testing of blood, swabs and tissues for EHV-1 and -4 were consistently negative over the next several days.
On April 27, additional PCR testing from two laboratories confirmed the EIV as equine H3N8 type of flue virus.
On April 28, additional necropsy and laboratory test results confirmed pneumonia caused by H3 equine influenza virus complicated by bacterial co-infection as the cause of death in more animals. EHV-1 and EHV-4 were not detected.
On May 2, further testing of the samples positive for the equine influenza virus determined the virus to be the Florida Clade 1 sublineage.
The EDCC noted that contributing factors to this outbreak included a history of gather and removal of West Douglas horses after a severe wildfire in their herd area, plus severe winds and dust storms in the area in the days before the outbreak. The West Douglas horses had been in the facility for about 9 months but were 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 in pens 40-43 were either unvaccinated, had only received one shot, or only recently received their booster shots about 10 days before the outbreak.
For more information go to the BLM website.
To read or download the May 3 BLM Situation Report click here.