Two Maryland horses test positive for neurologic form of equine herpesvirus.

The cases are not connected to each other, nor recent cases in Florida; Precautionary "hold" order placed on four barns at Laurel Park Racetrack

Two horses in Maryland have tested positive for the neurological form of equine herpesvirus type-1 (EHV-1), according to the Equine Disease Communication Center (EDCC). 

The two cases are not connected to each other, nor are they connected to recent cases in Florida. The Florida cases have raised concerns about the spread of a particularly aggressive form of EHV-1 from the Europe.

EHV-1 most often causes mild-to-moderate respiratory illness (rhinopneumonitis), but the infection occasionally leads to the life-threatening neurologic disease equine herpesvirus myeloencephalopathy (EHM). The mechanisms through which EHV-1 produces neurologic disease are not yet understood.

Learn more: Read “When EHV-1 Turns Deadly.” 

The first Maryland horse diagnosed with EHM this month was a 3-year-old Thoroughbred gelding stabled at Laurel Park Racetrack in Anne Arundel County. The gelding developed clinical signs—including ataxia and trouble urinating and defecating—on March 6. He was transported to the Marion Scott Dupont Equine Clinic in Leesburg, Virginia, and placed in isolation. Testing confirmed the diagnosis on March 8. The gelding remains isolated at the medical center and is responding well to treatment, according to information provided to the EDCC

While no other horses are showing clinical signs at this time, the Maryland Department of Agriculture (MDA) has placed four barns at the racetrack on a precautionary hold order, prohibiting movement on or off the premises until any exposed horses have been cleared for release. 

The second horse, stabled at a private facility in Cecil County, began displaying clinical signs of EHM on March 5, according to the EDCC. The horse did not respond to treatment and was euthanatized. Tissue samples subsequently tested positive for EHV-1 on March 8. The barn has been placed on a hold order, with veterinary professionals monitoring all horses for clinical signs. The hold order will remain in place until all exposed horses have been cleared for release.

There is no vaccine that specifically protects against EHM, so biosecurity is a crucial part of prevention. EHV-1 spreads from horse to horse through nasal discharge or aerosol droplets. Humans can pass along the virus via contaminated hands, clothing and equipment.

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