Equine herpesvirus myeloencephalopathy (EHM)

On December 4, 2009 The Miami Herold reported:

Calder Race Course on Thursday placed a fourth barn under quarantine because a horse there showed signs of a possible neurological disorder.

On Monday, Calder put three barns under quarantine after a horse tested positive for an equine herpesvirus. Bill White, trainer of that horse, has horses in all three barns.

That horse, which Calder has not identified, was euthanized on Monday at the University of Florida College of Veterinary Medicine in Gainesville.

The horse a Calder veterinarian examined on Thursday showed symptoms similar to those of the first horse that became ill, said John Marshall, Calder's vice president and general manager for racing.

Calder expects results of tests on the horse on Saturday, he said. It will then determine whether to remove the fourth barn from quarantine.

By adding that barn, the number of horses under quarantine expanded from 56 to 118.

Calder has about 1,800 horses in its stables.

Through Dec. 21, horses in quarantined barns cannot race and cannot train during the same hours as other horses.

Although the article did not identify the herpes virus responsible for this outbreak, it most likely is related to EHM.

What is EHM?


Equine herpesvirus myeloencephalopathy (EHM) is another name for the neurologic disease associated with equine herpesvirus (EHV) infections.  Neurological signs appear as a result of damage to blood vessels in the brain and spinal
cord associated with EHV infection. Interference with the blood supply leads to tissue damage and a subsequent loss in normal function of areas in the brain and spinal cord.

What are the equine herpesviruses?


To date, nine EHVs have been identified worldwide. Three of these—EHV-1, EHV-3, and EHV-4—pose the most serious health risks for domesticated horses and can have significant economic impacts on the U.S. equine industry.

• EHV-1: Can cause four manifestations of
disease in horses, including a neurological
form, respiratory disease, abortion, and
neonatal death. EHM is most often due to
mutant or neuropathogenic strains of EHV-1,
so called because of a particular mutation in
the genome.
• EHV-3: Causes a venereal disease called
equine coital exanthema that affects the
external genitalia.
• EHV-4: Causes a nonfatal upper respiratory
tract disease in foals and is uncommonly
associated with abortion and rarely with
neurologic disease.

To learn more about this disease, the USDA has a very informative  brochure at 


http://www.aphis.usda.gov/publications/animal_health/content/printable_version/equine_virus_brochure_2009.pdf