Kentucky EHM Case Count Increases to Six
Following last week’s confirmation by Kentucky’s State Veterinarian of a 3-year-old Thoroughbred filly with equine herpesvirus myeloencephalopathy (EHM, which results from equine herpesvirus, or EHV), officials have reported positive EHV (neuropathic strain) tests for five additional horses. The five were moved into isolation.

The number of horses exposed also increased. An additional 24 horses in Turfway Park’s Barn B were sampled on March 12, due to potential indirect-transmission exposure prior to the index case’s positive test result. Two of those horses showed trace EHV-1 DNA on nasal swabs and were isolated on March 14.

On March 15, officials reported that the index case was euthanized after her condition deteriorated.

As of that date, 18 horses in Turfway Park’s Barn A, where the index horse resided, and 22 horses in Barn B, had one set of tests (nasal swab and/or blood) with negative results. The last horse with fever left Barn A for isolation on March 10 and no clinical horses have resided in Barn B since the outbreak began. The last elevated temperature occurred on Mar. 12.

Enhanced biosecurity procedures and temperature monitoring continue in multiple sanctioned training venues in the state.

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 equine herpesvirus myeloencephalitis (EHM, the neurologic form).

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 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.