Trainers and racecourses have been told to be on guard after it was revealed Victor Dartnall's Devon stables have been temporarily shut down following an outbreak of equine herpes virus in the form of equine neurological disease.
Dartnall, whose stables are at Higher Shutscombe near Barnstaple, had runners as recently as Saturday at Wincanton, while his last winners came at Exeter and Chepstow earlier this month.
It is possible his horses may have been carrying the disease before they showed any symptoms and while it is difficult to spread, the British Horseracing Authority is taking every precaution to keep the outbreak under control.
In a statement, Professor Tim Morris, BHA's director of equine science and welfare, said: "We have been working with the trainer and his veterinary surgeon to ensure that the correct, robust security measures have been put in place.
"It is in theory possible that horses may have been infectious before the signs of the disease appeared. We have therefore alerted racecourse, trainer and veterinary representatives to possible exposure, but stress the actual risk of transmission of this virus in a controlled raceday environment is relatively small.
"This emphasises the importance of trainers being vigilant for signs of disease and in particular they should refer to the NTF Code of Practice for Infectious Diseases of Racehorses in Training, which contains specific advice on surveillance and what to do if they have concerns that a horse in their care is showing signs of the disease."
A statement on behalf of Dartnall said: "Over the last few days we have suffered an outbreak of a neurological disease in some horses. Initial test results support the cause to be neurological herpes virus. We are working very closely with our vets and the BHA and we are hopeful that we have the situation under control."
BHA spokesman Robin Mounsey said: "Obviously no entries can be accepted from the stable until the outbreak is cleared.
"The racecourses where Victor's horses have raced in the last couple of weeks have been informed. They will carry out their own procedures for ensuring the racecourse is completely clear of infection.
"They are precautionary as it is a very difficult disease to spread. Everything is being done as a matter of thoroughness. It is dreadful news for Victor's yard. For racing it is an issue that is very easily contained. Victor has done everything spot on. He's quite distraught and it is very sad news for him."
24 April 2014War saunters to easy success
Quevega five-timer still on course
Wylie trio go for Gold
Cyclone blows into Punchestown
Rain set to help Punchestown
Rifles aimed at York
Dante considered for Arod
Carpenter faces stamina question
Tonto strives for Sandown scalp
Telescope sights fixed on Sandown
Prize lined up for Greffulhe raid
Celebration time for super Sire
Taghrooda swerves Sandown heat
Concorde checks in for Punchestown
No Sandown run for Oscar
Un De Sceaux to skip Punchestown
Treve among stellar Ascot entries
Charline still in Guineas mix
Big guns remain in Guineas frame
Prince in Punchestown frame
Sparrow set for Punchestown spin
Balder to take novice test
Connell eager for Tank chase run
23 April 2014Telescope tops Richards runners
No rush for Annie target
Cosgrave appeal set for Monday
Hughes set for Sandown return
France adds flair to Guineas
Mullins drops Vautour Champion hint
Exciting Bunker given Dante date
Culloty keen on Gold run for Heeled
Hannon triple-handed in Guineas
Resurge revived for Epsom return
Sandown option for Battalion
Johnston pair clash in Derby Trial
Reckless Abandon returns to track
22 April 2014Rizeena delights in Guineas workout
Carberry targets swift return
Williamson escapes serious injury
Rizeena thrills Brittain on gallops
Door bags National glory
Twiston-Davies hits four-timer
Joe suffers shock defeat
Scudamore hits century mark
Ivan lands Fairyhouse prize
Thousand shows star quality
Cirrus set for Treve clash
Houblon heads Gold contenders
Guineas still on Berkshire radar
21 April 2014Door bags National glory
Wilson passes away
Ivan lands Fairyhouse prize
Stepper set for trip drop
Richards in Telescope sights
Ladies geared for Summer repeat
Hill out of Irish National
No Dundeel at Royal Ascot
Clowance up for the Cup
Garner hit with lengthy ban
Memories in Final flourish
Fitz powers home at Fairyhouse
Toner hits target for Elliott
Joe ready for Cork outing
Lennon looking to call tune
Ground holds key to Tonto show
Lucky escape for Cook
Mind called up for National service