The mare displayed neurological signs including ataxia (incoordination), neck pain, and proprioceptive deficits in her hind end. She was isolated for treatment at a veterinary hospital and remains alive.
Officials quarantined her home premises and enacted enhanced biosecurity protocols, and horses’ temperatures are being taken twice daily.
The mare did not travel recently, nor has she any links to any other EHV-1 cases. The home premises, however, hosted an event on March 21, and one asymptomatic horse stabled at the affected horse’s home premises competed in an event March 19-21. CDFA has notified event managers and encourages the owners of all potentially exposed horses to monitor their horses’ temperatures twice daily, restrict movement, and enhance their biosecurity procedures for the next 14 days. CDFA continues to monitor exposed horses.
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.