Equine Herpes Virus (EHV-1) is a highly contagious virus that is spread from horse to horse through direct contact, on feed, tack and equipment or on the clothes and hands of horse owners.


Most commonly, EHV-1 causes respiratory disease or abortion in pregnant horses, but a random mutation has lead to a neurologic form that affects the brain and spinal cord. The incubation period is typically 2-10 days. Signs of EHM include:

  • Fever (>102F)
  • Nasal discharge
  • Lack of coordination
  • Hind-end weakness
  • Lethargy
  • Urine dribbling
  • Diminished tail and anal tone


The cause is a herpes virus, EHV-1. There are many equine herpes viruses that have been identified but EHV-1 has been most recently associated with several large outbreaks causing respiratory and neurologic disease.


Diagnosis is made from blood samples and nasal swabs and can detect the disease even in horses that are not yet showing clinical signs. Samples can be tested for the presence of viral DNA by PCR or antibody titers can be detected in the serum. When antibody titers are used, you must demonstrate a 4-fold increase in a titer over 2-4 weeks to confirm infection.


Treatment generally consists of supportive therapy; intravenous fluids and nutrition, anti-inflammatory drugs and other intensive care. Anti-viral drugs are available but their use has had varied success in horses and research is currently underway at University of Oklahoma to find an effective and affordable drug to use in these cases. Vaccines are available against EHV-1 unfortunately these vaccines do not protect against the mutated strain that causes neurologic disease.


Prognosis depends on severity and duration of signs. Horses that retain the ability to stand on their own have a much higher survival rate than horses who become recumbent.