Neurologic EHV-1 Confirmed in California Horse
In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. | Photo: Stephanie L. Church/The Horse
The California Department of Food and Agriculture (CDFA) has reported a case of equine herpesvirus myeloencephalopathy (EHM, resulting from equine herpesvirus or EHV-1) at a boarding facility.

A 12-year-old Warmblood gelding in Los Angeles County displayed neurologic signs of the disease, with veterinarians confirming him positive for EHV-1 on March 9, 2021. Following an assessment of the home premises by CDFA personnel, 45 potentially exposed horses have been quarantined with enhanced biosecurity measures and twice-daily temperature monitoring. The owners of all exposed horses have been notified, and veterinarians have not identified additional cases at this time. CDFA continues to actively monitor exposed horses.

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).

equine herpesvirus
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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.