Mid-Winter Disease Outbreaks: Equine Herpes Virus, State by State

Equine herpes virus is in the news again. In late January, horses were newly affected in New Mexico, Arizona and Illinois, just as quarantines for previous cases were winding down in Pennsylvania and California.

Some people think of winter as cold and flu season. Others think of it as EHV season. Across the nation, EHV cases erupt onto as the temperature drops. Since the change of seasons also coincides with a massive migration of horses from north to south in the United States, the problem is not limited to northern states.

No two outbreaks are alike, nor is the access to information the same from state to state. The response is also very different based on whether affected horses were contained at a racetrack or training center, or if they were farm-based horses.

The impact of the outbreak, however, can affect horses and horse-related events and activities across a state where an outbreak has occurred. It can also result in the travel restrictions for horses that reside in or that have competed in a state where an outbreak occurs.

New Mexico racetrack

The first racetrack situation was at Sunland Park in New Mexico, near the Texas border. As of Saturday, January 30, 28 horses have been diagnosed as positive for EHV-1 on nasal swab and/or whole blood, according to the New Mexico Livestock Board.

“These horses are from 17 different barns within Sunland Park racetrack; at present, horses in surrounding areas have tested negative,” the Board warned on Saturday. “Of these 28, four horses have been euthanized for progressive neurologic signs. No movement of horses is being allowed in or out of Sunland Park. Officials with the Livestock Board, Racing Commission and Sunland Park will continue to work together to resolve the issue.”

Biosecurity measures being taken include isolating horses confirmed to have EHV-1; cleaning and disinfecting any surfaces or items horses may come into contact with; controlling foot traffic within the racetrack; providing plastic boot covers for personnel whose movement around the premises is essential; and sanitizing footwear and clothing.

“It’s mandatory that, twice a day, the temperature of every horse on the grounds is taken, logged, and reported to both Sunland Park and to the Racing Commission,” said Dan Fick, acting director of the New Mexico Racing Commission. Fever is a major indicator of EHV-1.”

In addition, track authorities suspended racing after the outbreak was announced to the public on January 22. Racetracks across the country closed their gates to horses that had been at Sunland.

Arizona racetrack

On January 26, Turf Paradise racetrack in Arizona closed its gates to horses that had been racing at Sunland Park in New Mexico. Two days later, the track quarantined a group of three horses that had arrived from the same county in New Mexico where the outbreak there occurred. One of the horses began to show symptoms of infection.

Acting State Veterinarian Sue Gale, DVM said in her latest report on January 28, “The case is not confirmed by testing yet, but (EHV-1 is) considered to be probable case of the virus.”

The Daily Racing Form reported the same day that the horse had been euthanized.

Illinois farm outbreak

Also on January 28, the Illinois Bureau of Animal Health and Welfare received notification of laboratory confirmation of EHV-1 (neuropathogenic form) infection in horses being boarded at a private stable in that state’s DuPage County.

State officials did not identify the breed or type of horses affected, but the stable has been placed under quarantine by state animal health officials. The source of the exposure is unknown.

At the time of the initial notification, eight horses were affected with two being subsequently euthanized. News sources reported that two horses were euthanized.

Also on January 28, Fox Valley Equine Practice in La Fox, Illinois reported a confirmed case of neurologic disease associated with EHV-1 in Kane County, which adjoins DuPage County. Both counties are near Chicago.

Illinois officials recommended the following procedures for exposed horses: “All exposed horses should have rectal temperatures taken twice daily (8-12 hours apart) and recorded in a log for at least 7 days after the date of potential exposure. Horses whose rectal temperature registers higher than 101.5 degrees Fahrenheit are considered to be febrile. All horses on the premises should also be monitored for neurologic signs (ataxia, posterior incoordination, weakness, recumbency with inability to rise, circling, head pressing, head tilt, bladder atony) during the home quarantine period. Central nervous system signs, such as posterior incoordination, weakness, recumbency with inability to rise, and bladder atony are most common in EHM affected horses.”

Other states

January quarantines in California and Pennsylvania are winding down. The California case, closed on January 26, concerned a single draft-cross that tested positive on January 6. The Pennsylvania case involved show horses and began on December 22. Four horses died there. No new cases have been reported in those states.

What can you do?

The key to all outbreaks is the mingling of horses or contamination between horses by caregivers and equipment. In this age of horses on the move, it is important to monitor the movement of horses to and from your property: If someone is arriving back from a show in the middle of the night, make sure that clear instructions are left to put that horse in the proper place, separate from other horses.

Do you know where every horse on your property has been in the last month? Sometimes people leave for a weekend and go to a trainer, but stable somewhere else. Or, they stop somewhere overnight coming or going to a show. It’s important that owners or riders keep a list of the names, locations and contact information for anywhere their horses were stabled.

If you share your trailer, clean it thoroughly, inside and out, after other horses have been in it. Don’t share tack or blankets or buckets. New Mexico officials had some good recommendations, such as lot letting the tip of a hose touch a horse or the ground, picking up manure immediately, using one water bucket per horse, and remembering to disinfect yourself, by spraying your clothing, head to toe, with Lysol disinfectant.

When you go to a show or event, get to know the people who stable their horses near yours. Where have they been, and where are they going next? What have they seen? Rules for biosecurity at shows are up to the show management, until or unless a horse is ill. You may be interested to know that some shows have more strict–or more lax–rules from the ones you normally encounter at your shows.

Stay in touch with your state’s animal health office, and watch for news online. Ask your veterinarian to keep you informed of any news about diseases that might affect your horse at home or on the road, and of any changes in the timing of health certificates or vaccinations required for travel.

Remember that a quarantine may affect not just the location of an infected horse, but every place an infected horse has traveled. Recently, horse owners in New Jersey were concerned because a horse that later tested positive for EHV in another state had been at a horse show in New Jersey. 

Most of all, if you feel that rules–or adherence to rules–is too lax at your boarding barn or at a show, make your concerns known. No one ever expects to be affected by an outbreak, but when one happens, it can affect horses who had very little to do with the actual infected horses. 

Note: Tomorrow, February 2, a presentation on biosecurity, vaccine strategies and the health of the performance horse will be held at the Ocala Breeders Sales Company in Ocala, Florida. Dr. Britt Conklin of Boehringer Ingelheim will present the latest information, beginning at 6:30. The event is sponsored by Peterson and Smith Equine Hospital.




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