Several outbreaks of equine influenza across Europe have prompted the BHA to issue a warning to British racing professionals, a development it has described as concerning.
Outbreaks have occurred in vaccinated horses in France, Belgium and Ireland, with three in unvaccinated horses in Britain.
In a notice posted to the BHA's Racing Admin site, the statement reads: "The BHA would like to make trainers and other industry participants aware of several outbreaks of equine influenza in France, Belgium and Ireland, some of which have occurred in vaccinated horses."
The statement then lists 11 known cases, beginning with four in France in December. Four have been reported in the UK since January 2: three have been in unvaccinated horses, although the vaccination status of the fourth case, discovered on Friday, is not yet known.
Two cases were reported in Ireland on Thursday, one of which concerned a vaccinated thoroughbred animal.
The statement added: "While we have not seen equine influenza in vaccinated animals in the UK, these reports are concerning. We would advise trainers to be extra vigilant with biosecurity and ensure all vaccinations are up to date. New horses entering a yard should be isolated for a period of 14 days.
"Horses showing signs that could be flu (especially rapidly spreading nasal discharge and/or harsh dry cough) should be promptly investigated by your vet. These symptoms may only be transient in vaccinated horses. The Horserace Betting Levy Board (HBLB) will cover laboratory costs for testing for equine influenza at the Animal Health Trust, if submitted under the HBLB scheme."
Equine influenza is an airborne infection and can travel, so it can be difficult to contain. The statement concluded by reiterating that all cases must be reported to the BHA.