Memories of the foot-and-mouth crisis came flooding back to many trainers as they dealt with the outbreak of equine influenza that has brought racing to a standstill.

The British Horseracing Authority (BHA) announced three further positive results on Friday, all from the Donald McCain yard, which was identified as the original source of the outbreak.

However, in what could be a worrying development, the BHA revealed what it described as “a separate suspicious case” had been identified at another, as yet unnamed, yard.

While that has yet to be confirmed as a positive sample, the clear concern is that no links have been identified between this stable and McCain’s. This yard had runners at Newcastle on Tuesday and Wolverhampton the following day, and so the BHA has placed a further 54 trainers who also had runners at these fixtures on hold and ordered testing of their horses.

This is in addition to the 120 trainers whose horses had come into contact with McCain-trained runners this week.

Of the four horses from McCain’s yard who competed at fixtures this week, one has returned a positive sample so far – Raise A Spark, who ran at Ayr on Wednesday. The test on this horse relates to a sample taken the following day. The horse showed no clinical symptoms on raceday.

Yesterday those 120 trainers had horses tested as the BHA sought to discover the scale of the problem it may face.

Lucinda Russell was one those trainers because she had runners at Ayr on Wednesday, one of three recent race meetings at which McCain-trained horses ran this week.

As with every other licensed yard, all the horses, even ones that have been retired from training, have previously been vaccinated and Russell has taken no chances.

“My vets have been here and all the horses have to have nasopharyngeal swabs, which takes a swab at the back of their throat,” she said.

“There’s been a bit of a crisis getting enough swabs but I’ve been to another local vet and got some more.

“We’ve got a hundred horses here, including ones not in training, but we’re testing every horse.”

Russell has two yards and the five horses who ran at Ayr have been isolated from the main part of her string as a biosecurity measure.

“We have two vets – one in each yard – to keep the biosecurity correct.

They’re walking around wearing disposable outfits, the staff either go to one yard or the other [to avoid cross-contamination].”

However, Russell believes that the BHA’s proactive strategy is correct if it avoids a repeat of events in 2001, when an outbreak of foot-and-mouth disease wiped out racing for two months in Britain, leading to the cancellation of the Cheltenham Festival.

“It’s just like when we had foot and mouth,” she explained. “We’ve got cars being sprayed, people using a foot bath and fresh clothes. Some of the girls here have got ponies of their own so they change before they come here just in case.”

“It can seem like using a sledgehammer to crack a walnut but it seems like the right thing to do.”

Any hopes for a resumption of racing on Wednesday will hinge on what progress is made with the current testing.

The BHA said: "It will not be possible to test every horse from every yard before the end of the weekend, but we will work with trainers to identify any priority or risk horses and ensure that they are tested.

"This will all form part of the picture that is built in order to assist the decisions that will be made on Monday."