Equine Herpes Virus Outbreak in 8 Western USA States, 2 Canadian Province

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Health officials inspecting horses during the 2006 equine herpes virus outbreak in South Florida. © Ken Braddick/dressage-news.com

At least 17 horses in eight western U.S. states and two Canadian provinces have been infected with the highly contagious Equine Herpes Virus-1, and at least three have died, according to state government animal health statements and news reports, leading to cancellation of many horse shows and clinics.

As of Thursday morning, the outbreak has affected horses in Arizona, Idaho, Utah, Colorado, California, New Mexico,Texas and Washington in the U.S. and Alberta and British Columbia in Canada. It has so far been confined to horses that participated in the National Cutting Horse Association’s Western Championships in Ogden, Utah early in May. About 400 horses took part in the competition.

Cutting-horse competitions scheduled for this coming weekend in nine states have been canceled; Washington State and Colorado State universities have quarantined their veterinary teaching hospitals; and clinics for reining and jumping in Colorado have been called off.

EHV in horses imported from Europe triggered an outbreak in South Florida, in December, 2006, leading to the deaths of six horses. Strict quarantine and biosecurity measures were imposed throughout the horse-intense area to stop the virus from spreading.

Ten cases of equine herpes Myeloencephalopathy caused by EHV-1 were confirmed Wednesday by the California Department of Food and Agriculture, which said the outbreak has been confined to horses that participated in the National Cutting Horse Association’s Western Championships in Ogden, Utah. About 400 horses took part in the competition.

The CDFA said in its latest report that positive confirmed cases were in Amador(1), Kern (2), Napa (1), Stanislaus(4), and Placer (2) counties.

One positive horse was euthanized after showing severe neurological signs associated with the disease while at the Kern County Cutting Horse Event on May 13 in Bakersfield, California. A second positive horse was transported from the Bakersfield event on May 13 to the University of California at Davis and is undergoing treatment.

All positive confirmed cases will be placed under quarantine.

The department recommended biosecurity measures for horses who attended the Odgen or Bakersfield events.

-Isolate exposed horse a minimum of 30 feet away from all other horses (round pen if necessary) for 21 days;
-Monitor temperature twice a day for 14 days;
-Immediately report temperatures over 102F (39C) to your private veterinarian;
-Use separate equipment, bucket, halters/leads for isolated horse;
-Wear protective clothing when handling isolated horse–coveralls, boot covers, gloves. Do not use same clothing with other horses;
– Ideally, use separate personnel for isolated horses, and
-Restrict movement.

Key to limiting the disease from spreading is Isolation of sick horses. Sick horses are shedding virus and should be removed from exposing additional horses.

The department said it is working with animal health officials in the Western states to investigate the source of the disease outbreak.

Washington state veterinarian Leonard Eldridge said a horse that was treated at the Washington State University Veterinary Teaching Hospital in Pullman tested positive for the virus.

“Symptoms in horses can include fever, sneezing, slobbering and other mild symptoms. Serious cases of the disease are rare, but can include staggering, hind-end paralysis and even death of the horse,” the vet said in a news release.

The virus can usually survive for about a week on surfaces, though under the right conditions it could last as long as 30 days, Idaho State Veterinarian Bill Barton said. That makes it particularly tricky to fight, because even the snort of an infected horse could spray nearby equipment or feed with the virus, said Debra Sellon, a veterinarian at Washington State University’s Veterinary Teaching Hospital.

Generally, fewer than half the animals that get the virus come down with the most serious neurological symptoms, Sellon said.

The National Cutting Horse Association’s website reported that all NCHA-approved shows scheduled have been canceled by the affiliates or show producers putting on the events.

“The NCHA appreciates this proactive move by show producers in a nationwide show of precaution and solidarity,” the group said. “While reported cases of the virus are currently in Western states, the interstate transport of infected horses could cause a much wider spread of the virus if we are not all very cautious at this time.”

The American Association of Equine Practitioners said:

• There is no specific treatment for EHV-1, although antiviral drugs (i.e. valacyclovire) may have some value before neurological signs occur.

• Non-specific treatment may include intravenous fluids, and other appropriate supportive therapy.

• The use of anti-inflammatory drugs (NSAIDs) is strongly recommended.

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.

Horses infected with the neurologic strain of EHV-1 may show signs including nasal discharge, lack of coordination, hind-end weakness, lethargy, urine dribbling and diminished tail tone. Veterinary treatment may include intravenous fluids, anti-inflammatory drugs and other appropriate supportive treatment. Immediate separation and isolation of identified suspect cases and implementation of appropriate biosecurity measures are key elements for disease control, CDFA reports.

Currently, there is no equine vaccine that has a label claim for protection against the neurological strain of the virus.