Authorities placed the premises under quarantine in October when one horse, a gelding with unreported vaccination status, tested positive for the neurologic form of EHV-1, also known as equine herpesvirus myeloencephalopathy (EHM). The affected horse first experienced clinical signs of ataxia (incoordination), fever, nasal discharge, and recumbency (inability to rise) on Oct. 12.
Nine other horses on the affected farm were quarantined and monitored for signs of illness. Two horses subsequently spiked mild fevers that resolved, and an additional horse on the premises exhibited fever and neurologic signs that resolved spontaneously after three days. No other horses or premises have been reported in connection with the index case.
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, weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency 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.