EHV-1 Outbreak: The Watch for Cases Continues

Several states affected by the neurologic equine herpesvirus-1 (EHV-1) outbreak saw more horses test positive for the disease Thursday, while other states saw their totals remain steady. Now, nearly two weeks after the conclusion of the competition believed to be the point of origin for the outbreak (the National Cutting Horse Association's [NCHA] Western National Championships, held April 29-May 8 in Ogden, Utah), veterinarians are diagnosing and treating both confirmed and suspected EHV-1 cases in an attempt to slow or stop the spread of the virus.

Equine herpesvirus-1 is highly contagious and can cause a variety of ailments in horses, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and myeloencephalopathy (the neurologic form). The virus is not transmissible to humans. Clinical signs of EHV-1 myeloencephalopathy include fever, ataxia (incoordination), weakness or paralysis of the hind limbs, and incontinence. The virus is generally passed from horse to horse via aerosol transmission (when affected animals sneeze/cough) and contact with nasal secretions.

At press time, the state and province totals of positive and suspected EHV-1 cases were as follows:

Washington - Debra C. Sellon, DVM, PhD, Dipl. ACVIM, a professor of equine medicine at Washington State University (WSU), confirmed today that two horses at the WSU Veterinary Teaching Hospital tested positive for EHV-1.

"We now have two confirmed positives that are presumed to be secondary infections," Sellon said, adding that these infections were likely transmitted from a horse that competed at the NCHA show and was treated at WSU for unrelated reasons. After confirming that the index horse was EHV-1 positive, the VTH quarantined its facility and staff members have been monitoring the patients' temperatures twice daily.

"We had two this morning with fevers that are positive, but there are no neurologic signs in any of the horses at WSU," she added.

The two new positives bring Washington's total to five positive cases of EHV-1*.

California - The number of horses with confirmed cases of EHV-1 has reached 13 in California (one of which was euthanized). Five of the positive horses displayed neurologic signs, whicle the other eight only presented with a fever, according to a May 19 release from the state's Department of Food and Agriculture. The infected horses are quarantined in the following counties: Amador(1), Glenn(2), Kern (2), Los Angeles(1), Napa(1), Placer (2), Plumas (1), and Stanislaus (3). The release noted that no travel restrictions or new requirements for horses entering the state are in effect.

Oregon - The state Department of Agriculture confirmed in a press release that a second horse tested positive for the neurologic form of EHV-1 yesterday (May 19). This horse is located in Umatilla County (Northeast Oregon), and the department's news release indicated this horse had been in close contact with horses that attended the Utah show.

Colorado - The Colorado Department of Agriculture reported that as of today, nine horses have tested positive for EHV-1, two of which euthanized after displaying severe neurologic clinical signs*. There are 22 suspected cases and 10 properties under quarantine.

Alberta - Chief Provincial Veterinarian Gerald Hauer, DVM, confirmed today that no new cases of EHV-1 were confirmed Thursday. The province's total of EHV-1 positive horses remains at three. Hauer also noted that two of the positive horses have not displayed neurologic signs at this point.

Idaho - According to a release on the state's Department of Agriculture, "one horse, which tested positive for EHV-1, was euthanized after showing severe neurological signs associated with the disease. A second horse was euthanized with similar (clinical signs) but no testing was completed."

There are 13 suspected EHV-1 cases currently under quarantine, the release said, adding that a total of 36 horses from Idaho attended the show in Utah.

Arizona - One horse that displayed severe neurologic signs tested positive for EHV-1 in Arizona. The most recent press release from the state's Department of Agriculture (dated May 18) indicates that other exposed horses in the state remain under quarantine and veterinary observation.

New Mexico - The New Mexico Livestock Board's website still indicates only one confirmed case of EHV-1 (the horse was euthanized after displaying neurologic signs).

Utah - A statement on the Utah Department of Agriculture's website indicated that no new cases of EHV-1 were confirmed Thursday, leaving the total number of EHV-1-positive horses in the state at five*.

British Columbia - The Ministry of Agriculture in British Columbia is reporting no positive EHV-1 tests at this time. The ministry also reports that "the neurological strain of EHV-1 is not reportable in British Columbia under current legislation which was written in 1948." The legislation is in the process of being updated, however, and EHV-1 will be listed as a reportable disease.

Texas - The USDA's May 19 situation report indicated that there was one confirmed case of neurologic EHV-1 in Texas.

Nebraska also no reports of EHV-1, but five farms remain under precautionary quarantine because they house horses that returned from the Utah competition.

Montana, Nevada, and Wyoming are still EHV-1-free, according to the state officials, and South Dakota State Veterinarian Dustin Oedekoven, DVM, confirmed today that the state has still not received any reports of EHV-1 positive or suspect cases.

Nicola Pusterla, DVM, PhD, Dipl. ACVIM, an assistant professor in the Department of Medicine and Epidemiology at the University of California, Davis, suggested that the horse-owning public take this outbreak as an initiative to create daily biosecurity programs at their own facilities.

"People are asking, 'What should we do now?'" Pusterla said. "Well, we should institute common-sense biosecurity protocol independent of an outbreak status. People should wash their hands, avoid commingling horses, (and) disinfect equipment (regularly). That won't necessarily prevent an outbreak, but will probably minimize the extent of the spread."

*Information regarding these horses' clinical signs was not immediately available.

About the Author

Erica Larson, News Editor

Erica Larson, News Editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in three-day eventing with her OTTB, Dorado, and enjoys photography in her spare time.

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