Grand National winning trainer Donald McCain has confirmed his three horses are the ones who've been diagnosed with equine influenza.
All four of today's race meetings in Britain have been cancelled as a precaution against the illness spreading.
A decision has now been made to cancel all meetings in the country until at least next Wednesday.
Three horses belonging to McCain have tested positive at his Bankhouse Stables in Cholmondeley, despite being vaccinated against the disease.
The National Trainers Federation has issued a statement on his behalf: "I have been aware of the recent news about Equine Influenza outbreaks in France and Ireland, and over the last couple of days, I have been concerned about the health status of a small number of horses in the yard.
"Their welfare is at the front of our minds, so at my request, our veterinary surgeon has examined them regularly and we have followed his advice on testing and treatment. It was by following this protocol that the positive results for equine flu came to light yesterday evening.
"The BHA (British Horseracing Authority) were contacted immediately and we are liaising closely with them about biosecurity and management of all the horses at Bankhouse.
“Bankhouse follows all the available advice on disease control and all our horses are fully inoculated. We are scrupulous about observing the health status of horses in our care and taking the necessary steps to treat any condition that may affect them. It follows we would never race any horses that we could have known were infected. Over the last 2 months, all potential runners have been scoped and their blood checked within 36 hours of their races to ensure that only healthy horses compete for the yard.
“When new horses arrive at our yard we, as much as possible, try to keep them separate but at this stage cannot know if the infection came from recent arrivals or from horses returning from racing.
"We have 3 confirmed cases and this morning have taken blood and swabs from all the others for testing.”
Following this afternoon’s announcement from BHA, we can confirm that racing at Uttoxeter on Saturday 9 February will not go ahead. Customers who have booked tickets should contact the racecourse office on 01889 562561 who will be able to organise an exchange or refund. pic.twitter.com/tH0PfSR7br— Uttoxeter Racecourse (@UttoxeterRaces) February 7, 2019
The BHA issued a statement earlier: "We are working quickly to identify the extent of the infection and will have more information when further test results are returned today. The results from those tests will not be known until this evening. Following these results being known a call will be convened to discuss the implications and a decision will then be made as to the impact on racing in the coming days.
"We are aware that people want to know the situation as regards racing tomorrow and this weekend and we will seek to provide more clarity as soon as we are able. It is likely that any definitive decisions on whether racing can take place tomorrow will be taken later this evening.
"We are contacting trainers of all yards which might conceivably have had contact with horses from the affected yard in order to advise them on biosecurity measures and to ask them not to move horses. We are also issuing guidance to the wider population of trainers.
"All British race horses are vaccinated against equine influenza. However this strain has affected vaccinated horses. The disease may be serious in unvaccinated horses, although symptoms in vaccinated horses are usually mild and transient. Symptoms may include a raised temperature, a cough and nasal discharge. It is highly contagious. Humans are not at risk from the virus though can be transmitters of the virus."