Alameda County, California
The California Department of Food and Agriculture (CDFA) has released the following statement about a recent neurologic equine herpesvirus-1 (EHV-1) case in the state:

“An 8-year-old Thoroughbred mare in Alameda County displaying neurological signs on January 12 was confirmed positive for EHV-1 on January 19. The mare resided at a racetrack and was transported to her home barn in Sonoma County and isolated on January 12 following the onset of clinical signs. The mare has been quarantined at her home premises and will be released following two consecutive negative tests seven days apart. Fourteen horses from the index mare’s training barn have been isolated, quarantined, and have tested negative for EHV-1; an additional 13 horses from the adjoining training barn have also been quarantined, with no additional clinical signs or cases detected at the racetrack. CDFA was onsite to conduct a site assessment and implement enhanced biosecurity measures including twice daily temperature monitoring. Site assessment at the racetrack confirmed no known exposure beyond the barn identified, and there has been no evidence of ongoing disease transmission.”

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.