On May 23, the Equine Disease Communication Center (EDCC) shared an update from the Pennsylvania Department of Agriculture (PDA) regarding a case of equine herpesvirus-1 (EHV-1) confirmed last week in Chester County.
“The Chester County, Pennsylvania, horse that tested positive for EHV-1 died on May 17 in isolation on a private farm,” the PDA said via the EDCC. “The post-mortem results indicate that the horse died of an unrelated medical issue, not from equine herpes myeloencephalopathy (EHM, the disease caused when EHV affects the central nervous system). There have been no other horses showing signs of EHV-1 infection and there is no ‘outbreak’ as has been reported elsewhere.
“The horse had been placed in isolation at its home farm on May 15 when it began to show signs of illness, including abnormal gait and stance and a high fever. As EHV-1 was detected in the horse’s nasal swab sample, all horses at the Chester County farm were quarantined. Based on the post-mortem findings, the low levels of EHV detected on the nasal swab sample, and the absence of EHV-related illness in any of the horses on the premises, there appears to be little risk even for the horses that were in direct contact with the horse that died.
“Furthermore, the two horses that had moved off the farm prior to the horse getting sick pose an even lower risk of spreading EHV-1. These two horses have returned to the home farm, also remain under close monitoring, and have shown no signs of illness. Following national guidelines, and in consultation with EHV regulatory experts, the horses on the home premises will remain under quarantine with monitoring for a minimum of 14 days from when the affected horse was isolated (beginning May 15). No quarantined horses have shown any signs of illness to date. EHV-1 causes illness in some horses and others may carry virus without showing clinical disease. In particular, horses that are under stress may be more likely to shed the virus.”
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 myeloencephalopathy (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 the neurologic form 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 present 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.