MORE UPDATES – Equine Herpesvirus Outbreak

May 17th, 2011 8:57 AM | No Comments

Equine herpes virus outbreak grows; California state veterinarian confirms 10 new cases


National Report — The California state veterinarian’s office reports 10 new cases of equine herpes virus (EVH-1) have been confirmed today.

The multi-state EHV-1 outbreak is spreading with cases now extending beyond Colorado and Washington state.

The outbreak was traced to the National Cutting Horse Association’s Western National Championships in Odgen, Utah on April 30-May 8, as previously reported by DVM Newsmagazine. The latest EHV-1 cases in California are located in Kern, Placer, Stanislaus, Amador and Napa counties in California, according to the California Department of Food and Agriculture.

“One horse in Kern County was euthanized after showing severe neurologic signs often associated with the disease,” CDFA reports. “All of the infected horses recently attended the National Cutting Horse Association’s Western National Championships in Odgen, Utah on April 30-May 8, 2011, where they were most likely exposed to the virus. All California horses that have been in contact with an infected horse and show signs of disease or test positive for (equine herpes myeloencephalopathy) will be placed under a CDFA quarantine in order to limit spread,” the agency says.

California veterinary officials also report they contacted 54 exhibitors from California who participated in the Utah event and asked them to isolate and monitor their horses for clinical signs of EHV-1.

Officials say this outbreak is evolving and remains national in its scope.

As previously reported, two cases of EHV-1 have been confirmed in Colorado. More cases are suspected in multiple other Western states. Of the two confirmed cases, both horses have been euthanized, according to the Colorado Department of Agriculture. At least six Colorado horses in four counties are showing symptoms of the disease and are under quarantine.

As a result of the outbreak, Colorado State University’s (CSU) Veterinary Teaching Hospital announced May 16 it is immediately restricting all non-emergency equine and camelid veterinary appointments to prevent further exposure. The same measures were instituted at WSU and the University of California-Davis.

Officials from the National Cutting Horse Association (NCHA), which hosted the Utah event, says it received credible, but unconfirmed, reports of cases not only in Colorado and Washington, but also in Oregon, Arizona, California and Western Canada. The Washington Department of Agriculture is also reporting cases in Idaho and Utah.

Horse owners are being advised to notify veterinarians if they participated in the NCHA event or if their horse suddenly comes down with a temperature above 102-degrees-F, which typically precedes clinical signs.

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This from the American Quarter Horse Association: “AQHA is asking show managers to voluntarily cancel or postpone shows that are in areas where the virus has been located.  If you have any questions regarding your area, you should contact your state association or your state veterinarian.”


UPDATE from Texas Animal Health Commission…

Equine Herpesvirus Awareness

An outbreak of Equine Herpesvirus (EHV-1) has been traced to horses that attended the National Cutting Horse Association’s (NCHA) Western National Championships in Odgen, UT on April 30 – May 8, 2011.  Affected horses have been identified in Colorado. Additional states have possible cases pending and/or are looking for animals that attended the event and returned home.

Texas does not currently have any confirmed positives. The Texas Animal Health Commission (TAHC) has identified all horses that attended the show in Utah and are currently working on contacting the equine owners and advising them to isolate exposed horses for at least two weeks, follow good biosecurity practices and watch for possible clinical signs.

EHV-1 Information
Equine Herpes Virus is a common virus in equine populations worldwide. There are several strains of the virus, with EHV-1 and EHV-4 being most often involved in clinical disease. EHV-1 can cause respiratory disease, abortion and neurologic disease. The neurologic disease is sometimes referred to as Equine Herpes Myeloencephalopathy (EHM.)  Although EHV-1 is highly contagious among horses, it does not pose a threat to human health.

EHV is transmitted primarily by aerosol and through direct and indirect contact.  Aerosol transmission occurs when infectious droplets are inhaled.  The source of infectious droplets is most often respiratory secretions.   In the case of abortions, virus may be present in the placenta, fetal membranes and fluid, and aborted fetuses.
Direct horse-to-horse contact is a common route of transmission of the virus, but indirect transmission is also important. This occurs when infectious materials (nasal secretions, fluids from abortions, etc.) are carried between infected and non-infected horses by people or fomites (inanimate objects such as buckets, etc).

Signs of EHV-1
Fever is one of the most common clinical signs and often precedes the development of other signs.  Respiratory signs include coughing and nasal discharge.  Abortions caused by EHV generally occur after 5 months of gestation. Neurologic signs associated with EHM are highly variable, but often the hindquarters are most severely affected. Horses with EHM may appear weak and uncoordinated.  Urine dribbling and loss of tail tone may also be seen. Severely affected horses may become unable to rise.

It is important to remember that none of these signs are specific to EHV, and diagnostic testing is required to confirm EHV infection.  Also, many horses exposed to EHV never develop clinical signs.

What to do if you suspect your horse has been exposed
If you suspect your horse has been exposed to EHV, contact your veterinarian.  In general, exposed horses should be isolated and have their temperatures monitored twice daily for 10 days.  If an exposed horse develops a fever or other signs consistent with EHV infection, diagnostic testing should be performed. Testing of healthy horses is generally not recommended.

Useful Links/Resources


Several reported cases of Equine Herpesvirus occurred and were documented in several horses attending the NCHA Western National Championships in Ogden, Utah April 29 – May 8. The virus can be contagious among horses, but is NOT transmittable to humans. While the NCHA does not want to unnecessarily alarm horse owners, they do want to be a clearinghouse of factual information so you can make informed decisions on this matter regarding your personal horses.

As a precautionary measure, the Board of Directors of the Breeders Invitational cancelled that event that had been scheduled for May 14 – 28 in Tulsa, Oklahoma, and the NCHA cancelled the Mercuria/NCHA World Series of Cutting event that had begun in conjunction with the BI in Tulsa. While no horses currently in Tulsa for the BI or the World Series of Cutting have exhibited any clinical signs of EHV, the governing bodies for the events made the decision to cancel the shows to ensure the maximum health and safety of horses scheduled to participate until additional information on the extent of the several EHV cases reported in other state(s) can be determined.

Click here to continue reading this article at the NCHA website…


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