In a Nov. 27 update, officials at the Oklahoma Department of Agriculture, Food and Forestry (ODAFF) confirmed that eight additional horses in Remington Park’s second quarantined barn have tested positive, via polymerase chain reaction (PCR), for equine herpesvirus-1 (EHV-1). The positive horses, which are clinically normal (not showing any signs of illness), were moved to the isolation barn. The index case remains the only horse to develop neurologic signs. Remington Park is in Oklahoma County.
Following the index case, a 3-year-old filly, and the subsequent isolation of 66 horses exposed in the filly’s barn, ODAFF officials announced on Nov. 21 that two additional horses—one in the index case’s barn and one from another barn—tested positive for EHV-1. Officials reported that 100 horses in the second barn were subsequently quarantined.
Following these confirmations, officials in New Mexico and Kentucky restricted horses from Remington Park from entering racetracks in their states.
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.