Take precautions with Equine Herpes Virus-1 (Rhino)
A recent outbreak of Equine Herpes (Myeloencephalopathy) Virue-1 (EHV-1) has been reported among horses that attended the National Cutting Horse Association’s Western National Championship in Ogden, Utah from April 30 through May 8, 2011. Horses who participated in this event MAY have been exposed to this EHV-1 virus. At this time we have not confirmed any cases in Oregon but are contacting all horse owners who attended the event with their horse(s).
Even though EHV-1 is not a regulatory disease, and is not reportable, we are asking all veterinarians to call our office with any CONFIRMED cases (503-986-4680).
Veterinarians should work closely with their equine clients to develop plans that address the clients’ ability to prevent EHV-1 in their hoses. And, if a horse is suspected of having the viral disease, it should be isolated. Equipment should not be shared.
Enforcement of strict biosecurity measures and hygiene practices are likely to be more effective than widespread vaccination in reducing the risk of acquiring infection. Nevertheless, recent research demonstrates that viral shedding is much reduced in horses with high circulating titers of virus-neutralizing (VN) antibody, as well as in horses that have been vaccinated recently with the Rhinomune MLV vaccine.
Following are links for EHV-1 from the California Department of Food and Agriculture and UC Davis that will help readers become informed about this disease.
The full text of the California Department of Food and Agriculture may be access at:
The full text of UC Davis Center for Equine Health disease information and links may be accessed at: http://www.vetmed.ucdavis.edu/ehv1_general.cfm
Some of the points made on these Web sites are summarized below.
Potential Clinical Signs of EHV-1
- Respiratory signs (Signs may be minimal and of short duration.):
l Increased rectal temperature may be the only clinical sign
l Horses can have two fever spikes
l The initial rise in rectal temperature is usually mild – 101.5 to 102.5°F
l 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.
- Neurological signs:
l Horses become ataxic (in coordination), 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.
- Pregnant horses can experience spontaneous abortion between 7 days and several months after exposure. The mare will exhibit limited initial signs.
l 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.
l Stress and lack of previous exposure to the virus may make the horse more susceptible to becoming clinically ill.
l Currently, there is no equine vaccine that has a label claim for protection against the neurological strain of the virus.
l It is virtually impossible at this time to know if horses in our native population have ever been naturally exposed to recently diagnosed strains of EHV-1 and whether these individuals develop any subsequent immunity to the virus.
l EHV-1 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.
l It is felt that horses with severe clinical signs of neurological EHV-1 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.
l As with all contagious diseases, if horses are commingled with strange horses, an unknown degree of inherent risk exists for exposure to EHV-1. 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 EHV-1 infected individuals, there is no foolproof way to completely eliminate the risk of exposure.
l 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 EHV-1.
Don Hansen DVM, MPVM – State Veterinarian
Animal Health & Identification, Oregon Department of Agriculture