Oklahoma Racehorse Euthanized Due to EHV-1
The Oklahoma Department of Agriculture, Food and Forestry (ODAFF) confirmed on Nov. 14 that a 3-year-old Thoroughbred filly was euthanized due to the severity of her clinical signs of the neurologic form of equine herpesvirus-1 (EHV-1). She first experienced signs, including acute onset, ataxia (loss of control of body movements), fever, and recumbency (inability to rise), on Nov. 12.

“ODAFF was informed last night of a positive EHV-1 test sample from a horse stabled at Remington Park,” said Michael Herrin, DVM, ODAFF assistant state veterinarian. “The horse was euthanized Tuesday evening and the barn it was housed in is currently under quarantine.”

The barn housed 66 other horses, which are now sidelined from racing for at least 14 days, during which they will be monitored for clinical signs and temperature exceeding 101.5°F.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM.

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months), but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with the neurologic form (equine herpesvirus myeloencephalitis, or EHM) usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.