California Confirms Another EHM Case
On Mar. 15, officials at the California Department of Food and Agriculture (CDFA) confirmed a horse in Sonoma County with equine herpesvirus myeloencephalopathy (EHM, which results from equine herpesvirus, or EHV). The 21-year-old Warmblood mare experienced onset of clinical signs on Mar. 13. Signs consisted of ataxia (incoordination) in all four limbs and urine dribbling.

The horse is alive and undergoing treatment while isolated at a veterinary hospital. Forty horses on her home premises remain under quarantine with enhanced biosecurity protocols and twice-daily temperature monitoring in place. CDFA states that no known risk of exposure exists at this facility or other local events. The affected horse did not travel recently and isn’t connected to any other EHV-1 case.

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.