Trainer Kevin Ryan has been suspended from running horses after a case of equine herpes was found at his yard.
Only one case has been discovered in Ryan’s string but the yard near Thirsk has been placed under quarantine by the British Horseracing Authority (BHA).
The nearby stables of trainers Bryan Smart and Michael Herrington have also been quarantined as a precaution.
The BHA said they are working with Ryan and staff to ensure the correct disease control measures are in place.
“The risk of the virus being transmitted in a controlled race-day environment is relatively small,” said David Sykes, the BHA’s director of equine health and welfare.
“[But] it is in theory possible that horses from the yard in question may have been infectious some time before the disease was diagnosed.
“For this reason we have taken measures to alert trainers, as well as racecourses and veterinary surgeons, to be vigilant to the clinical signs.”
The equine herpes virus can cause respiratory disease and abort foetuses, while a less common neurological form of the virus can cause co-ordination problems and paralysis, and is potentially fatal.
The National Stud breeding site in Newmarket was closed last year following the discovery of the neurological herpes virus infection.
Ryan won the French Derby and Irish Champion Stakes in 2014 with The Grey Gatsby and is a four-time winner of the Ayr Gold Cup, including the 2016 edition with Brando.