National Stud at Newmarket Quarantined for EHV- 1

National Stud at Newmarket Quarantined for EHV- 1

An electron microscope view of EHV-1.

Photo: Walid Azab, PhD

Halfway through the quarantine period following a case of the neurologic form of equine herpesvirus-1 (EHV-1) in the National Stud in Newmarket, England, no new cases have been discovered.

“We are still observing the guidelines set out in the code of practice, and the infection remains isolated to just that one filly,” said National Stud spokeswoman Amy Taylor.

A young maiden mare was imported from France on Jan. 20 for live cover at the stud, but began to show signs of illness after a week in the stud’s health isolation unit (where all imported horses are kept for two weeks following arrival). She had difficulty getting up from lying down and had problems urinating, the facility’s staff reported. Veterinarians sent samples for testing, and the stud immediately stopped all animal transport in and out of the stud on Jan. 28. Two days later, when laboratory testing showed positive results for EHV-1, public visits to the stud were suspended, as well. As the virus can spread via clothing and other materials, the stud is allowing only necessary workers, who are following strict biosecurity procedures including protective clothing and shoe disinfectants, to access the facility.

As the Thoroughbred breeding season opens, the infection is all the greater risk to the industry as it spreads quickly and can cause abortion, stud officials said.

The imported mare was confirmed as up-to-date on her vaccines, including EHV vaccines, Taylor said. However, current EHV vaccines are not entirely protective, EHV researchers say.

“The vaccines on today’s market cannot prevent the infection, and herd immunity in many countries is low,” said Walid Azab, PhD, of the Virology Institute at Freie University, in Berlin, Germany, and the Department of Virology, Faculty of Veterinary Medicine at Zagazig University, in Egypt. “So that means the circulating strains in the field can overcome the immunity arising from the vaccine.”

Health Alert: Equine Herpesvirus

Even though she was vaccinated, the infected mare can develop symptomatic disease and shed the virus to other horses while the infection is active, he said. Once she’s healed, the mare will always carry the virus, in a latent state (which does not shed). However, various situations can cause the virus to reactivate in the mare’s system.

“Travel, extreme heat, extreme cold, excessive training, social stress—any kind of stressful scenario threatens to reactivate the virus in an EHV-positive horse, throughout its life,” Azab told The Horse.

However, that’s not necessarily a reason to euthanize the horse, he added. With good intensive care, some horses can overcome neurologic disease, but “there’s no guarantee,” he added. Pre-infection vaccination, good preventive health care and biosecurity practices, and careful monitoring are usually good ways to keep the horse safe, Azab said.

“In any case, no country is free of EHV—except Iceland,” he said. “So it’s out there. The idea, then, is to keep it as controlled as much as possible through good biosecurity measures.”

In the future, improved vaccines could help eliminate signs of disease in vaccinated horses, he said. His laboratory is working with mutated strains that are currently in the in-vivo testing phase with their American collaborators. Azab said his group will present preliminary results of that study at the International Equine Infectious Diseases conference this April in Argentina.

As for the infected filly at Newmarket, she will return home to France once she’s recovered from her illness, the stud’s representatives said. Currently she’s showing marked improvement and is expected to make a full recovery. Stud officials hope to reopen the stud for breeding operations by mid-February.

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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