EHV-1 Outbreak: Several New Cases Reported

There were only a few new cases of equine herpesvirus-1 (EHV-1) diagnosed Friday related to the outbreak believed to stem from the National Cutting Horse Association's (NCHA) Western National Championship, held April 29-May 8 in Ogden, Utah.

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 (EHM) 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 today (May 21), the state and province totals of positive and suspected EHV-1 cases were as follows:

California - The number of positive EHV-1 cases in California rose to 16 with the report of an additional confirmed case today. A statement released by the California Department of Food and Agriculture indicated that 15 of the horses with confirmed cases competed at the NCHA show in Utah. Six of the EHV-1 positive horses displayed neurologic signs while the others have only displayed a fever, the statement said.

The department is also investigating a positive EHV-1 case that does not appear to be related to the NCHA competition.

"A suspect case of equine herpes myeloencephalopathy was investigated by Animal Health Branch veterinarians," the statement read. "This mare did not participate in the National Cutting Horse Association's Western National championships in Ogden, Utah from April 30-May 8, 2011 ... This mare is exhibiting neurological signs compatible with a number of equine diseases or conditions. Three sets of nasal swabs and blood testing on this mare indicate she is negative for the mutant strain of EHV-1 that causes EHM and she is positive for the common strain of EHV-1 that most commonly causes respiratory signs but may also cause neurological signs in a low percentage of these cases."

The mare is currently receiving "intensive supportive care" at the University of California, Davis, Veterinary Medical Teaching Hospital.

Texas - A May 20 statement from the Texas Animal Health Commission noted that there is still only one EHV-1 positive horse in the state (it was not reported if that horse displayed neurologic signs). There is one suspected case. A total of 25 horses from Texas attended the NCHA competition in Utah, the statement said.

Idaho - A statement released by the Idaho State Department of Agriculture today indicated that no new cases of EHV-1 had been diagnosed in the past 24 hours. Previous releases from the department indicated that "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."

New Mexico - According to a May 19 statement from the state's Livestock Board, there is still only one confirmed case of neurologic EHV-1 in New Mexico (the horse was euthanized). The statement indicated that other exposed horses were quarantined and under veterinary care.

Oregon - There are still only two confirmed cases of neurologic EHV-1 in the state, according to the Oregon Department of Agriculture. (The latest update from Oregon came May 19.)

Utah - A May 20 statement from the Utah Department of Agriculture noted that no new cases of EHV-1 had been confirmed, leaving the total number of EHV-1-positive horses in the state at five. The clinical signs associated with the positive horses were not reported.

Washington - The total number of confirmed cases of EHV-1 in Washington stands at five, reported the state's Department of Agriculture on May 20. Two of the five positive horses did not display any neurologic signs; however, information about the clinical signs the other three displayed were not immediately available.

Alberta - Chief Provincial Veterinarian Gerald Hauer, DVM, indicated May 20 that there were three positive EHV-1 cases in Alberta. Two of the three did not display any neurologic signs.

British Columbia - The province's Ministry of Agriculture noted Friday that there were no confirmed cases of EHV-1.

Colorado - The number of confirmed EHV-1 cases in Colorado stands at nine, according to the most recent release from the state's Department of Agriculture (dated May 20). The release noted that two of the positive horses were euthanized after displaying severe neurologic signs. No information was available about the clinical signs found in the other seven horses.

There are 22 suspected cases of EHV-1 in the state, and 12 facilities have been placed under quarantine by the Department of Agriculture.

Arizona - The most recent statement released by the state's Department of Agriculture (May 18) indicated that there was still only one confirmed case of neurologic EHV-1 in Arizona. The statement indicated that other exposed horses in the state are under quarantine, but no further information was available.

Montana, Nebraska, Nevada, North Dakota, South Dakota, and Wyoming remain free of positive EHV-1 reports.

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 eventing with her OTTB, Dorado.

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