The 11-year-old Paint stallion is the fourth horse to develop the neurologic form of EHV-1, and an additional five horses have developed fevers exceeding 101.5°F. Three of the neurologic horses were euthanized due to the severity of their clinical signs, and all other horses on the premises are reported as recovering. CDFA continues to monitor the outbreak.
For the complete outbreak history, see
- California Horse Succumbs to EHV-1
- Second California Horse Succumbs to Equine Herpesvirus Myeloencephalopathy
- Third EHV-1-Infected Horse Dies in San Bernardino County, California
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 the neurologic form (equine herpesvirus myeloencephalitis, or 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 spreads easily via nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or by way of clothing, hands, or equipment of people who have recently had contact with an infectious horse. Establish and maintain routine biosecurity measures, including hygiene and basic cleaning and disinfection practices 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 controlling the disease is preventing it.