Dear Clients, Trainers and Barn Owners:

 

There are currently four Oregon horses that have tested positive for Equine Herpes Virus -1 (EHV-1) with one of the horses being positive for the mutated EHV-1 neurological herpes virus, Equine Herpersvirus Myeloencephalopathy (EHM). The EHM horse was euthanized. The EHV-1/EHM confirmed cases are located in Clackamas, Umatilla, and Deschutes counties. The positive tested cases are directly linked to the National Cutting Horse Association competition held in Ogden Utah from April 29^th – May 8^th.   There were a total of 20 horses from Oregon that attended the championship competition in Ogden. These 20 horses reside on 16 different locations in the state and have exposed an additional 120 horses to the virus. 

 

EHV-1 is a highly contagious disease with an incubation period of 24 hours to 8 days or more with the typical time being 4 to 6 days. When neurological disease occurs it is typically 8 to 12 days after the primary infection. The virus is estimated to be viable outside the horse’s body for up to 7 days under normal circumstances, but can remain alive for up to 30 days, depending upon environmental conditions.

 

The clinical signs of infection start with a rectal temperature at or above102 F. This temperature increase is a biphasic (two-phase) fever peaking on day 1 or 2 and again on day 6 or 7. With the respiratory infection there is often serous or mucoid nasal and ocular discharge, but not a lot of coughing. There may be some persistent enlargement of the lymph nodes under the jaw. With the neurologic form of the disease there is minimal respiratory signs with fever (temp 102 F or greater) being the only indicator. Neurologic disease appears suddenly and usually rapidly progresses within 24 to 48 hours from the onset of neurological signs. Clinical signs of the neurologic disease may include; nasal discharge, incoordination, hind limb weakness, loss of tail tone, lethargy, urine dribbling, head tilt, leaning against a fence or wall to maintain balance, inability to rise. 

 

EHV-1 is contagious and transmitted by direct contact with an infected horse via respiratory tract nasal secretions or the air around the horse that is shedding the virus.   The disease can also be spread indirectly through contact with physical contaminated objects such as; human contaminated hands or clothing, contaminated equipment and tack, contaminated trailers, wipe rags and other grooming equipment and contaminated feed and water buckets.

 

Once a horse has been exposed to EHV-1, the virus replicates and travels up the nose of the horse and into the lymph nodes under the jaw. After more replication in the lymph nodes the virus goes inside white blood cells and then travels throughout the body in the blood stream, this is called viremia. With EHM the infected white blood cells attach to the blood vessels surrounding the spinal cord. The virus then causes an ischemic (or stroke like) event at that location and the blood flow to the spinal cord is disrupted resulting in neurological disease.   Because the virus travels inside white blood cells in the blood stream, antibodies which fight the disease can not reach the virus. For that reason there is no specific vaccination or evidence at this time that current EHV-1 vaccines can prevent EHM.   The more potent EHV-1 vaccines have been shown to reduce nasal shedding and in some cases reduce viremia (virus circulating in the blood). These products may therefore have some theoretical value against EHM (by reducing viremia), and certainly against the spread of the virus. The more potent EHV-1 vaccines include Rhinomune, Calvenza, Pneumabort-K and Prodigy.    In my opinion, the Calvenza 03 Flu/Rhino vaccination that Oregon Equine administers is the most effective flu/rhino vaccine on the market.

 

The best practice to help control the spread of the disease and try and keep your horse(s) safe is to avoid other horses for at least the next 2 weeks, through the first week of June and monitor your horse(s) rectal temperature am & pm daily.   Barns should enforce no horses in or out through the first week of June. If the EHV-1 and EHM numbers continue to increase, keep your horse(s) at home in isolation and keep barns closed. If the case numbers are going down then figure out the exposure risk you may be taking and decide if you want to take your horse out of their safe environment or open your barn. To learn more about EHV-1 and EHM and track the case numbers visit the American Association of Equine Practitioners web site, www.aaep.org. Scroll down to the horse owners section and there you will find accurate information, the situation report and links to the various state veterinary web sites that list the number and types of cases in the affected states.

 

If it is not possible for you to avoid contact with other horses, then the following biosecurity measures should be taken; wash hands with soap and water or use alcohol based hand sanitizer after touching each horse, spray shoes with a 1% -3%  bleach solution, change your cloths and take a shower prior to seeing your own horse(s).

 

If you have a horse that has been off of your property and is going to return, please call to discuss further biosecurity guidelines.

 

Normal rectal temperature for a horse is 99.0 – 101.5. If your horse has a temp above 101.5, or is showing any of the clinical signs of EHV-1 and EHM call on the emergency line. If you have any questions please call and leave a message. I will return your call. 

 

 

Sincerely

 

Dr. Wilson