EHV-1 Kills Two Michigan Racehorses

At least two horses at Northville Downs Standardbred racetrack in Northville, Mich., contracted equine herpesvirus type 1 (EHV-1) and were euthanatized. The first case was discovered Dec. 14, when a 6-year-old Standardbred gelding began exhibiting classic signs of the neurological form of herpesvirus type-1 (EHV-1) myeloencephalopathy (EHM). After the horse was taken to the Diagnostic Center for Population and Animal Health at Michigan State University (MSU), the preliminary diagnosis was confirmed.

The EHV-1 organism can cause several forms of disease, including rhinopneumonitis (a respiratory disease found mostly in young horses), abortions in pregnant mares, and neurologic disease.

Elizabeth Carr, DVM, assistant professor of large animal clinical sciences at MSU, treated the affected Standardbred when it arrived on campus. "When the horse arrived, he was dribbling urine and his hind end was very weak and unsteady," she said. "These two clinical findings coupled with the history of rapid onset and progression of clinical signs made EHM one of our top differentials in this animal." The infected horse was euthanatized the next day.

Upon discovery of the disease, the track was quarantined and 25 horses have been monitored closely for clinical signs. According to Steve Halstead, DVM, MS, symptoms of EHM include fever, cough, runny nose, and neurological deficits, and they typically appear within 21 days of exposure. The Michigan Office of Racing Commissioner and the State Department of Agriculture are coordinating the investigation of the potential outbreak, and monitoring of the quarantined horses. Another horse at the racetrack tested positive for EHV-1 on Dec. 20 and, according to Halstead, was euthanatized and incinerated at the MSU Diagnostic Center for Population and Animal Health.

EHV-1 is not necessarily fatal, and Carr said treatment is possible. "Affected horses can deteriorate rapidly, becoming extremely weak and possibly recumbent within 24 hours of the onset of clinical signs," said Carr. "Treatment is largely supportive care, and trying to prevent or minimize secondary complications associated with recumbency. This would potentially include placing the affected animal in a sling, catheterizing the bladder, as well as fluid and nutritional support. Anti-inflammatory and antiviral medications are recommended to decrease the inflammation associated with the disease and to try to hasten recovery. Horses that remain standing have a better prognosis than horses that become recumbent and are unable to rise."

Halstead said Northville Downs remains open for live and simulcast horse racing. "The barn where the two (affected) horses were stabled is quarantined and will remain so, with all exposed horses prohibited from relocation until 21 days have passed since the time of removal of the two known cases; until the body temperature of any additional case horse returns to normal after its acute fever; or until the acute clinical signs have resolved if the horse is non-febrile," he explained.

Strict biosecurity measures have been taken at the racetrack and the veterinary hospital."The affected horse was admitted to a separate wing of the hospital and the area was closed off to all personnel other than those individuals directly involved in the care of the affected animal," explained Carr. "Foot baths and protective gear were used in addition to isolation. After euthanasia and removal of the affected animal, the area was disinfected and continues to be closed to new cases or foot traffic."

Horse owners with questions should contact the Michigan Office of Racing Commissioner at 734/462-2400, or the Michigan Department of Agriculture's State Veterinarian’s Office at 517/373-1077.

About the Author

John V. Wood

John V. Wood is an Emmy Award-winning journalist, and now teaches his craft to high school students in North Carolina. Wood has been published in numerous national magazines/newspapersover his career, and published his first book in June 2010. Wood currently lives in Willow Spring, NC.

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