EHV-1 Outbreak: New Cases Still Being Reported

More than three weeks after the first cases of equine herpesvirus-1 (EHV-1) related to the current outbreak were diagnosed, new confirmed cases are still being reported to state and provincial animal health authorities. The outbreak, which is believed to stem from horses attending an Odgen, Utah, cutting horse championship competition in early May, has now seen dozens of horses test positive for the disease, and more than 10 horses have been euthanized or died as a result.

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.

New Confirmed Cases

At press time (4:00 p.m. EDT), the following states and provinces had provided new information about the EHV-1 cases present within their borders:

California--A statement issued late Friday (June 3) by the California Department of Food and Agriculture indicated that one additional horses tested positive for EHV-1 that day; the total number of confirmed cases in the state is now 21, according to a statement release today. Eight of the EHV-1 positive horses have displayed neurologic signs and 13 horses have only been febrile (feverish). Animal health officials noted that "the two new confirmed positive horses, located on the same premises, were exposed to a previously confirmed positive Ogden, Utah, participant."

The confirmed cases are located in the following counties: Glenn, Plumas, and Shasta in Northern California; Amador, Colusa, Marin, Napa, and Placer in North Central California; Stanislaus in Central California; Kern in South Central California; and Los Angeles and Ventura in Southern California.

Saskatchewan--According to a release from the Saskatchewan Ministry of Agriculture Animal Health Unit, the province's first confirmed cased of neurologic EHV-1 was diagnosed last week. Disease surveillance veterinarian Wendy Wilkins, DVM, PhD, indicated in the release that the affected horse "attended a cutting horse show in Lloydminster, Saskatchewan, Canada, (May 14-15). Some of the horses present at this show may have had a history of travel to the National Cutting Horse Association's Western National Championships in Ogden, Utah, conducted (April 29-May 8)."

No further information was available about this new case at press time.

British Columbia--A statement released Friday by Equine Canada indicated that a total of two cases of EHV-1 have been confirmed in British Columbia: "The update in British Columbia, from the Animal Health Centre laboratory (Ministry of Agriculture), indicated two positive (neurologic) EHV-1 cases confirmed through the laboratory. These cases had either direct or indirect contact with horses that were at the Ogden, Utah competition." It is not clear what clinical signs these horses displayed.

No Change

  • Alberta-- 10 positives (four horses had no clinical signs but tested positive through laboratory testing, three had respiratory signs, and three displayed neurologic signs; one horse has died; however, it's unclear if that horse was neurologic or not)
  • Arizona--11 positives (one euthanized after developing neurologic signs; clinical signs of other cases not reported)
  • Colorado--9 positives (six horses have shown neurologic signs; the remaining three have displayed respiratory signs and/or a fever)
  • Idaho--8 positives (four EHV-1 positive horses have displayed neurologic signs; the rest have only displayed a fever)
  • Montana--0 positives
  • Nebraska--0 positives
  • Nevada--3 positives (two have displayed neurologic signs)
  • New Mexico--4 positives (USDA Situation Report indicates two have been euthanized; clinical signs not reported for other horses)
  • North Dakota--0 positives
  • Oregon--5 positives (one euthanized with neurologic signs; four showing no clinical signs)
  • South Dakota--1 positive (clinical signs not reported)
  • Texas--1 positive (officials believe it is not related to the outbreak, but is an isolated case)
  • Utah--8 positives (two euthanized after becoming recumbent, or unable to rise; clinical signs associated with the other confirmed cases were not reported)
  • Washington--8 positives (four did not display clinical signs; signs associated with other cases not reported)
  • Wyoming--0 positives

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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