Equine Herpes Myeloencephalitis (EHM) is a neurologic condition caused by EHV-1 (Equine Herpes Virus-1). The virus causes inflammation of the blood vessels in the spinal cord resulting in loss of neurologic function.

Horses affected by EHM usually have severe neurologic disease that affects the hind limbs, bladder and rectum. Horses are often wobbly, incontinent, and weak, but are usually alert and hungry. Horses in the early stages have a fever. Severely affected horses often are down and cannot rise.

Not all horses that acquire the EHV-1 infection develop these neurologic signs.

EHM is a reportable disease, meaning that if a horse has or is suspected of having this disease, vets are required to report it to agricultural authorities (usually the State Veterinarian). These authorities may investigate the case as part of a larger effort to monitor equine health and coordinate with other states and the USDA APHIS in preventing the spread of illness or disease on a national and international level.

Diagnosis is made using nasal swabs, PCR and blood tests.

Treatment is mostly nursing care and anti-inflammatories. Anti-viral drugs have been shown to be helpful in treatment.