EHV-1 Update
Posted on Mon, June 06, 2011

The Colorado Department of Agriculture continues to investigate the spread of Equine Herpesvirus (EHV-1) in the state.

As of 6/3/2011:

9 confirmed cases of horses with EHV-1
Two horses, which tested positive for EHV-1, were euthanized after showing severe neurological signs associated with the disease.
22 suspect cases.  NOTE: Suspect cases are those horses that are believed to have been exposed to EHV-1, show consistent clinical signs of the disease, and have confirmatory tests pending OR are horses showing clinical signs and located in a quarantined facility with a horse confirmed to have EHV-1 in which case, the decision to test will be made by the horse owner and their veterinarian. Release of the quarantined facilities will require EHV-1 testing to assure freedom of the disease.
12 quarantine and hold orders have been issued in 8 counties (Bent, Boulder, Garfield, Gunnison, Larimer, Mesa, Morgan, & Weld)
The Department is not making recommendations concerning the cancellation of events but reminds horse owners and event organizers that static EHV-1 case numbers do not signify the end of the spread of EHV-1.  There are many factors to consider when deciding whether to attend or host an event including the "herd health" of the incoming horses, the history of exposure, travel history of the horses, the management's health requirements for the horses entered in the event, the type of event, how the horses will be housed, the level of contact that the public has to the horses, and the degree to which horse equipment and tack will be shared. There are specific disease prevention practices or biosecurity procedures that can address each of these risk factors.

The University of California, Davis has produced an informative white paper on EHV-1, "Awakening the Dormant Dragon: Neurological Form of Equine Herpesvirus-1," that horse owners and event organizers may find especially useful in developing biosecurity practices to reduce risk of EHV-1 infection and other equine infectious diseases:

It is also recommended that all people within the horse industry regularly visit CDA's website at for the latest information and resources. Another vital resource for horse owners is their private practicing veterinarian. Their advice will be invaluable for horse health and to reduce the risk of EHV-1 and other equine diseases.

Facts about EHV-1 Vaccines
The common vaccines available for EHV-1 immunization do not protect against the neurological form of EHV-1 disease which is commonly called equine herpesvirus myeloencephalopathy (EHM). These immunizations do protect against the respiratory and abortion forms of the disease.

The EHV-1 vaccines are thought to reduce the shedding of the virus and may decrease the amount of circulating virus in the system of infected horses. So vaccinations prior to infection may help reduce the severity of an outbreak.

In the face of an EHV-1 outbreak, the value of vaccinating EHV-1 affected horses or exposed horses is questionable and may be detrimental to the horse. When an EHV-1 outbreak occurs, it may be helpful to give an EHV-1 booster immunization in a previously vaccinated, unexposed horse.
Consult with your veterinarian to determine the best vaccination and treatment strategy for your horses in your particular situation.

New Travel Requirements for Horses Entering Colorado
Standard requirements for horses entering Colorado include a health certificate issued within 30 days of their arrival and a negative Coggins test within 12 months.  The new requirement consists of a permit to enter the state.  Horse owners who wish to bring their horse into Colorado must first call their veterinarian.  That veterinarian can then contact the Colorado Department of Agriculture's State Veterinarian's Office at (303) 239-4161 and request a permit number.  That number would then be included on the health certificate.

Additional Travel Tips for Horse Owners Traveling To or From Colorado

1.      Contact the State Veterinarian's Office of the destination state to find out if travel requirements have changed for that state.

2.      Call organizers of the event to see if they have new health requirements or if it has been cancelled.

3.      If traveling, practice appropriate biosecurity measures.  Biosecurity tips may be found at

4.      Isolate any new animals and those returning to the home premises for three weeks when possible.

5.      Use separate water, feed supplies and equipment.

6.      Continue to monitor the CDA webpage at for further information to aid in the decision making for transporting horses.

If your horse attended the Ogden, Utah event:
CDA encourages all horse owners who attended the Ogden, UT, to notify their veterinarian and isolate and monitor their horses for clinical signs of the disease. These horses should have their temperature taken twice a day. Horses with elevated temperature can be sampled by a veterinarian to analyze whether their horse is shedding EHV-1.  Individual horse and barn bio-security is very important.  Some horses may not show signs of the disease but may still be a carrier. Those owners are also encouraged to restrict movement of their horses.

General Disease Information
EHV-1 is not transmissible to people; it can be a serious equine disease that can cause respiratory and neurological clinical signs; it can even result in death. The most common way for EHV-1 to spread is by direct horse-to-horse contact.  It can also be spread by contaminated tack, equipment, and people's clothing. In addition, the virus can be spread through aerosols (airborne) for a limited distance.

Symptoms include fever, decreased coordination, nasal discharge, urine dribbling, loss of tail tone, hind limb weakness, leaning against a wall or fence to maintain balance, lethargy, and the inability to rise. While there is no cure, the symptoms of the disease may be treatable.  Horse owners should isolate any sick horses and immediately contact their veterinarian.  Any individual horse with clinical signs consistent with neurological EHV-1 infection should be removed immediately from the area and placed in a separate enclosure for isolation.

Additional resources can be found at

The Department has received numerous calls from veterinarians, horse owners and media. To help facilitate a timely response, please see the following list.

If veterinarians or horse owners have questions about the disease, testing, or other aspects of the investigation:Contact your local veterinarian
Dr. Kate Anderson, 303-239-4161,
Dr. Carl Heckendorf, 303-239-4161,
If you are a media outlet and would like to set up an interview: contact Christi Lightcap, 303-239-4190,