Two horses on separate Deschutes County properties recently tested positive for the neurologic form of equine herpesvirus (EHV-1) and were euthanized, the Oregon Department of Agriculture confirmed on May 17.

The first horse was confirmed EHV-1-positive on May 4 after returning home from an April 22-25 event at the Oregon Horse Center, in Eugene. The horse showed neurologic signs without fever or nasal discharge and was subsequently euthanized.

The second horse began showing neurologic signs on May 13, having returned from a horse show at the Oregon Horse Center May 6-7. The horse was euthanized, and both horses’ home properties are under official quarantine for at least 28 days.

The Equine Disease Communication Center released this information on May 17, 2022.

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 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.