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Equine herpes virus

Lane County horses test positive for EHV

One Lane County horse has died and four others from the same stable have tested positive for a neurological form of Equine Herpes Virus (EHV-1). All horses on the property have been quarantined and those showing symptoms of the disease are being treated. There is no indication that the virus has spread to other horses beyond those being quarantined. The State Veterinarian is praising quick work by local veterinarians and Oregon State University’s Veterinary Diagnostic Laboratory (OSU-VDL) in detecting the virus quickly and taking steps to limit any spread.


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State vet recommendations for horse event managers for EHV-1

EHM continues to be is a reportable disease to the state veterinarian. For confirmed or suspect cases of EHM please call and report to Dr. Brad R. LeaMaster, state veterinarian at (503) 986-4680, immediately.
There are no restrictions on the movement of non-exposed horses within Oregon at this time.
Recommendations for horse show/event managers regarding Equine Herpes Virus (EHV-1) Biosecurity Procedures

These biosecurity guidelines have been developed based on currently available information, by ODA veterinarians and the faculty at the College of Veterinary Medicine at Oregon State University, to minimize the risk of transmission of infectious diseases at public equestrian events. If the situation changes, these and other guidelines will be modified as appropriate.
The EHV-1 virus is a naturally occurring virus of the equine population.  It may lie dormant in an infected animal for long periods of time and then re-activate during a period of stress resulting in clinical disease in the host as well as spreading to other horses in close contact.  The reasons why EHV-1 causes severe neurological signs in some but not all horses are not fully understood. Because this virus lies dormant in so many normal horses, there is never an "ALL CLEAR/ NO RISK" when horses commingle.  Horse owners should practice basic every day biosecurity if they want to protect their own horse(s) from exhibiting or being exposed to this virus as well as other highly contagious pathogens.
Based on what is known today, we are suggesting that managers of horse shows or events occurring in Oregon consider incorporation of the following biosecurity measures to minimize the disease risk for all participants. 
(These measures are directed at protection from not only herpes virus infections but from other highly contagious equine diseases including strangles and pigeon fever.)
  1. Since horse-to-horse contact is an important risk for many contagious diseases including EHV-1, event managers could allocate enough space in warm up and wash/clean up areas to minimize nose-to-nose contact between horses.
  2. Managers could further reduce the risk of disease spread from human hands by limiting access to horses by the visiting public and other contestants by establishing restrictive spaces in front of stalls and other places where horses are secured between show events (such as at trailers).
  3.  Managers could post information signs that advise contestants not to share equipment, including riding clothes, and to wash their hands before and after handling horses that belong to other people.
  4.  If horses are to be housed in stalls during the event, it is preferable that stalls have solid sides high enough to prevent horse-to-horse contact or droplet transmission. (We recognize that many event locations will not be able to offer such high walled stalls to their participants)
  5. For multi-day events, managers might consider establishing a "No Fever" policy for horses attending the event. Give the participants notice of the new "No Fever" policy before they arrive at the show grounds. Provide instructions for obtaining the horse's temperature and an index card on which to record temperature readings for each horse.
Suggested language for the "No Fever" policy follows.
  • All horses will have temperatures taken twice daily and results will be posted on front of the stall/pen/trailer for inspection.
  • Any horse will be subject to random temperature check by the show veterinarian or designated member of the veterinary staff during the event.
  • Any horse with a fever of 102°F or greater, unassociated with exercise in the preceding two hours, will be removed from the event and premises immediately (i.e., within 2 hours of detection of fever).
  • If the owner cannot move the horse off the premises, a professional horse hauler contracted by the event will remove the horse to a designated isolation area at the owner's expense.
  • NOTE: It is understood that some (most) horses with a fever will not have EHV-1; however, in the interest of conducting a safe event under the current circumstances, the no fever policy will be enforced. If you do not wish to comply with these safety measures please do not attend the event.
6.    Other suggestions to consider:
  • Communal stall cleaning equipment should be disinfected between each stall.
  • For large and/or multi-day events, managers should employ a veterinarian to be on the grounds for the event and not just on emergency call.
  There are no restrictions on the movement of non-exposed horses within Oregon at this time.
Recommendations for horse show/event managers regarding Equine Herpes Virus (EHV-1) Biosecurity Procedures in pdf format.

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The following link for EHV-1 and EHM virus infection from UC Davis may help readers become informed about this disease.

The full text of UC Davis Center for Equine Health disease information and links may be accessed at: http://www.vetmed.ucdavis.edu/ceh/ehv1_general.cfm

Another useful informational link: http://www.aphis.usda.gov/vs/nahss/equine/ehv

Highlights from the UC Davis report are summarized below:

Potential Clinical Signs of EHM
1.     Initial 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 respirator signs of nasal discharge, increased temperature (> 102.5), minimal coughing, can abort if pregnant, or, in a small number of cases develop neurological signs.
2.     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.
 3.  Additional information:
  • Many times when horses are incubating the virus, fever in excess of 102°F may be the only observable sign of infection. However, fever may not be present in all neurogenic clinical cases.
  • Stress and lack of previous exposure to the virus may make the horse more susceptible to becoming clinically ill.
  • Currently, there is no equine vaccine that has a label claim for protection against the neurological strain of the virus. However, vaccination may offer some protection against the neurological form of the virus.
  • EHM virus infected horses, whether clinically ill or not, may periodically shed both active and nonreplicating (dead) virus in their nasal secretions. If the virus being shed is active, these horses have the potential to spread the virus to other horses. Horse-to-horse contact, contaminated hands, equipment, tack, feed, and aerosol transmission all play a role in its spread.
  • It is felt that horses with severe clinical signs of neurological EHM illness often have very large viral loads in both their blood and nasal secretions. These high viral loads are thought to be a significant aspect in the transmission of the disease to exposed horses. Therefore rapid separation and isolation of identified suspect cases and biosecurity are key elements for disease control.
  • As with all contagious diseases, if horses are commingled with strange horses, an unknown degree of inherent risk exists for exposure to EHM. Many factors may enhance or reduce the amount of risk. If the choice is made to commingle with a population that has the potential to harbor EHM infected individuals, there is no foolproof way to completely eliminate the risk of exposure.
  • If horses are exposed to new horses, especially in stressful competitive environments or following long distance travel, it is helpful to establish a disease-monitoring plan under the advice of a veterinary practitioner.  Temperature monitoring (2x / day) is a tool to be used for a differential diagnosis that could include EHM.

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Equine virus brochure

Information on the equine herpes virus.
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