English trainers have been told to be on guard following the shut-down of trainer Victor Dartnall's Devon stables due to an outbreak of equine herpes virus in the form of equine neurological disease.

Dartnall had runners as recently as Saturday at Wincanton while his last winners came at Exeter and Chepstow earlier this month.

While the disease is difficult to spread, the British Horseracing Authority (BHA) 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 it was possible Dartnell's horses had been carrying the disease before they showed any symptoms.

"We have been working with the trainer and his veterinary surgeon to ensure that the correct, robust security measures have been put in place," Morris said.

"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 that the actual risk of transmission of this virus in a controlled raceday environment is relatively small."

BHA spokesman Robin Mounsey said every precaution was being taken.

"Obviously no entries can be accepted from the stable until the outbreak is cleared," he said.

"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.

"It was just earlier this week when a couple of horses' temperatures spiked and that is when they started to get concerned."