California officials imposed a quarantine at a San Mateo County horse facility after testing confirmed a pony positive for EHM.

EHV Cases Confirmed in California Horses: Quarantine

Equine Herpes Myeloencephalopathy (EHM) case

California officials imposed a quarantine at a San Mateo County horse facility after testing confirmed that a pony is positive for EHM. Equine Herpes Myeloencephalopathy (EHM) is the neurological form of EHV-1 (equine herpes virus).

The California Department of Food and Agriculture (CDFA) says the 15-year-old mare displayed neurologic signs prior to the diagnosis. Horses infected with the neurologic strain of EHV-1 show clinical signs that typically include mild incoordination, hind end weakness, and loss of bladder function.

Another mare from the property, a 24-year-old Tennessee Walking Horse spiked a fever and tested positive for EHV-1. It can cause respiratory disease, abortion in mares, neonatal foal death and neurological disease.



EHV is contagious

EHV-1 is highly contagious with an incubation period of 2 to 10 days. Clinical signs include fever, nasal discharge, depression, cough, lack of appetite, and potentially enlarged lymph nodes.

Veterinarians recommend vaccinating against EHV-1 to help prevent the virus. Although, there is no current vaccine that prevents the neurological manifestation of the infection.

Respiratory shedding of the virus generally occurs for 7-10 days. It may persist longer in infected horses. For this reason, a 21-day isolation period for horses confirmed positive with EHM is recommended along with stringent biosecurity protocols.

Similar to herpes viruses in other species, the latent form of EHV-1 can reactivate at a later date, but generally with a low viral load posing a low risk of infecting other horses.

Humans are not at risk of contracting the virus, however, humans can act as an indirect mode of transmission. Veterinarians recommend limiting horse to horse contact and horse to human to horse contact. They also add, avoid communal water sources at horse shows and other horse facilities. The virus spreads readily through direct contact with infected materials, including shoes, brushes, tack, and more.

Hand soap, alcohol-based hand sanitizers, and sunlight neutralize the virus.

EHM is a reportable disease in California.