Equine Herpes Virus-1 Alert: Oregon Cases Reported

Updated 8.6.07

According to State Veterinarian Don Hansen, a second case of Equine Herpes Virus-1 (EHV-1) has been reported in the state. During this same period, five horses in Washington also exhibited clinical signs that were consistent with EHV-1. All of these horses attended the same weekend show a few days before exhibiting signs of disease.

Even though EHV-1 is not a regulatory disease and is not required to be reported in Oregon, we believe it would be helpful to veterinarians and equine owners alike to have access to current and accurate information about this disease in our state.

Dr. Hansen advises veterinarians to work very closely with their equine clients to develop sound plans that address the clients’ ability and desire to prevent EHV-1 in their horse(s).

It is extremely important that cases of EHV-1 be reported to state-federal animal health officials so that current information be provided to veterinarians and equine animal owners.

Potential Clinical Signs of EHV-1 

• Respiratory signs: Signs may be minimal and of short duration.
  • Increased rectal temperature may be the only clinical sign
  • Horses can have two fever spikes
  • The initial rise in rectal temperature is usually mild-101.5 to 102.5°F
  • After the initial temperature rise, which may be missed, the horse can either be clinical normal, develop respiratory signs of nasal discharge, increased temperature (> 102.5), minimal coughing, can abort if pregnant, or, in a small number of cases develop neurological signs. 
• Neurological signs: Horses become ataxic (incoordination), inability to empty bladder, and weakness of the tail. Some horses will become completely paralyzed; the prognosis for these horses is poor. In a small number of cases, horses can show abnormal mentation and develop cranial nerve signs. Most horses become mildly to moderately neurologic and stabilize rapidly. The neurologic signs can persist but most horses are normal by 3 to 6 months after onset of clinical signs.  
• Abortion: Pregnant horses can experience spontaneous abortion between 7 days and several months after exposure. The mare will exhibit limited initial signs.

Consult your veterinarian with any concerns or questions you may have about EHV-1 and your horses.