Ludlow is not due to host another meeting for another fortnight, but Wolverhampton Racecourse has cancelled Saturday's fixture and is offering full refunds or transfers for everybody who pre-booked.
The British Horseracing Authority has confirmed three cases of equine influenza, triggering the cancellation of all racing in Britain for the next several days and the shutdown of training yards across the country.
"One would like to think this could go in a couple of days but the BHA are going to have to pull out all the stops to make sure this doesn't go through all the horse population".
Irish trainer Gordon Elliott ran a number of horses at Ayr on Wednesday but his runners were still travelling back home when the news of the positive tests broke and they were quickly placed in isolation away from his stables.
Leading Irish trainer Gordon Elliott had horses running at Ayr and has confirmed in his blog with Betfair.com that the horses in question are now quarantined in an isolation yard which is a 25-minute journey from his training base in Meath.
It is a highly contagious respiratory infection, causing symptoms similar to a flu in humans and lasting for about a week.
As a result, outbreaks are extremely rare, but the fact that all three of the horses affected at McCain's stable had been vaccinated prompted immediate concern that a new strain of the disease could spread rapidly through the racing industry.
The BHA is expected to announce on Monday plans for resuming racing but for now, racing has been halted until at least next Wednesday, Feb. 13.
In a statement, the BHA said: "This approach will allow samples to be collected and assessed by the Animal Health Trust in order that a fully informed decision can be made on Monday".
The BHA have responded to public concerns by providing a Q&A on equine influenza, which can be read here.
"We know we're not going to be in a position, given the incubation period of the disease, to make a decision about returning to racing until first thing next week at the very earliest".
McCain said: "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".
The virus then spread to reported cases in Britain and Ireland, with the BHA sending an official warning to the horse racing industry on January 19.