The updated report of Nov. 19 regarding the equine herpesvirus-1 outbreak in San Bernardino County stated that two additional febrile horses, an 11-year-old Paint mare and a 22-year-old Paint mare, were also confirmed positive for EHV-1.
The first (index) horse affected, a 13-year-old Quarter Horse mare, began showing clinical signs on Oct. 29 and was euthanized that day due to the severity of her clinical signs. She was confirmed positive upon necropsy on Nov. 5. CDFA quarantined 20 additional horses and enacted enhanced biosecurity measure, including twice-daily temperature monitoring.
The second deceased horse, a 22-year-old Paint gelding, was also euthanized due to the severity of his clinical signs. At that time, three additional horses on the premises with fevers exceeding 101.5° Fahrenheit were also confirmed positive for EHV-1.
CDFA continues on-site monitoring at the affected premises.
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 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.