EHM

The Michigan Department of Agriculture and Rural Development (MDARD) has announced the state’s first confirmed case of equine herpesvirus myeloencephalopathy (EHM), the neurologic form of equine herpesvirus-1 (EHV-1) this year.

“The 5-year-old Standardbred gelding from Washtenaw County tested positive for … EHM after developing a sudden onset of neurologic signs: weakness, incoordination in the hind limbs, and difficulty urinating,” the MDARD said in a March 27 Facebook post. “The horse is currently under veterinary care and is isolated. The stable where the horse originated from is under quarantine and is being monitored closely.”

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 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.