THE BHA have warned trainers to be vigilant for signs of disease after it was announced that Victor Dartnall's Devon yard had been temporarily closed due to the discovery of an outbreak of what is believed to be equine neurological herpes.

Professor Tim Morris, director of equine science and welfare at the BHA, said that horses may have been infectious before disease was diagnosed, although he said the risk of contagion was small.

He 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 contacted racecourses to alert them to possible exposure but stress that 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 recently published NTF (National Trainers Federation) Code of Practice for Infectious Diseases of Racehorses in Training, which contains specific advice on surveillance for this disease and what to do if they have concerns that a horse in their care is showing the disease."

In a statement Dartnall, who trains at Brayford in North Devon, 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."

The outbreak was discovered on Wednesday when temperatures spiked in some of Dartnall's horses. The most severely affected are believed to be the younger horses in the yard. Neurological herpes can be fatal.

Dartnall's yard will remain closed until the disease is under control.