Neurologic Equine Herpesvirus in Colorado

Three Colorado premises are under quarantines or hold orders due to confirmed equine herpesvirus or exposure to febrile horses that became neurologic.

Premises in El Paso County in Colorado had confirmed neurologic equine herpesvirus cases. iStock

The Colorado State Veterinarian reported confirmed cases of equine herpesvirus type 1 (EHV-1) in horses on two separate premises. Those horses had traveled to an event together in Scotsdale, Arizona. Both horses showed neurologic signs consistent with neurologic equine herpesvirus or equine herpesvirus myeloencephalopathy (EHM).

The following report from the Colorado State Veterinarian was provided by the Equine Disease Communication Center.

On April 9, 2021, the Colorado Department of Agriculture, State Veterinarian’s Office, was notified of a potential equine herpesvirus type 1 (EHV-1) case in El Paso County from a private practicing veterinarian. 

The case had originally presented with a fever of unknown origin on April 4. 

After several days with no resolution of clinical signs, the clinician submitted a respiratory panel, which came back positive for EHV-1. The index horse was stabled at a farm with 35 horses. 

After being made aware of the potential for EHV-1 in the index horse, the stable manager began to monitor temperatures on the other horses in the barn. Seven additional febrile horses on the premises were identified from April 7-9. 

A veterinarian submitted samples from a second horse on the premises, which also tested positive for EHV-1. 

Additionally, one of the febrile horses on the index premises began to show neurologic signs on April 11, indicative of equine herpes myeloencephalopathy (EHM). 

The State Veterinarian’s Office was made aware that a group of horses from the index premises and additional barns in the county had recently traveled together to attend an equine event in Scottsdale, Arizona, from March 14-29. 

An additional horse on a second premises that had traveled to and from the show was also found to be febrile. That horse developed neurological signs consistent with EHM on April 12. 

Both premises are under quarantine and are being monitored by the State Veterinarian’s Office and their private veterinarians. 

A third associated premises that also transported horses to the same event is under a hold order. That premises has had no febrile horses or horses with clinical signs consistent with EHV-1. 

The Colorado State Veterinarian’s Office has been communicating with the Arizona State—where the show was hosted—to provide notification to other event attendees. 

For more information on equine herpesvirus myeloencephalopathy download this Fact Sheet.

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