EHM Causes Equine Death in Minnesota

Equine herpesvirus myeloencephalopathy (EHM) caused a young Quarter Horse to be euthanized in Clay County, Minnesota.
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Clay County Minnesota map

A young Quarter Horse was euthanized due to EHM in Clay County, Minnesota.

A six-week-old Quarter Horse was euthanized in Clay County, Minnesota, on July 15, and post-mortem tests confirmed it was infected with the highly contagious disease equine herpesvirus myeloencephalopathy (EHM). The Minnesota Board of Animal Health is responding to the case by activating its EHM control plan and placing the Clay County farm under quarantine to closely monitor the remaining horses for EHM.

On July 15, the examining veterinarian observed the foal had worsening neurologic signs, including a loosely hanging lower lip, biting at his front legs, stumbling, circling and an inability to rise on his own, leading to the decision to euthanize the animal. It was submitted to the North Dakota State University Veterinary Diagnostic Laboratory for a necropsy, which confirmed infection with equine herpesvirus type 1 (EHV-1). The clinical neurologic signs described and positive EHV-1 test results resulted in a diagnosis of EHM.

“This case is a good reminder that despite the fact we’ve had no reported EHM cases in Minnesota since 2015, it still poses a significant risk to horses,” said Equine Program Director Dr. Courtney Wheeler. “Horse owners should take this opportunity to review their biosecurity protocols, both on the farm and when traveling, to ensure they are doing their best to protect their horses and Minnesota’s equine community from communicable and contagious diseases like EHM.”

The most common way for EHM to spread from horse to horse is by nose-to-nose contact. EHM can also spread by contact with contaminated objects such as tack, feed and water buckets, grooming equipment, and a person’s hands or clothing. Horses might appear healthy, yet still can spread the virus. Horse owners are reminded of the importance of adhering to stringent biosecurity practices to prevent the further spread of EHM and other contagious diseases. A general biosecurity steps flyer is available on the Board’s website.

Multiple EHM cases continue to be identified throughout the United States. Due to the highly contagious nature of this disease, all cases of EHM must be reported to the Board of Animal Health, which, in collaboration with Minnesota’s equine industry, enforces an official control plan for EHM. Under the plan, the Board is required to quarantine, test and monitor all horses confirmed to have, or been exposed to, EHM. You can review the EHM control plan on the Board’s website.

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