The loss of Musselburgh's richest ever jumps meeting on Sunday because of a UK-wide alert about an equine flu outbreak is "a real, real shame", the clerk of the course has said.
The British Horseracing Authority abandoned the meetings after learning of three confirmed EI cases in vaccinated horses from an active racing stable.
It also means that the seven races at Newbury, including the Betfair Hurdle and the Denman Chase, have had to be cancelled.
Equine influenza is a highly infectious disease of horses, mules and donkeys.
It is the most potentially damaging of the respiratory viruses that occur in United Kingdom equines and disease symptoms in non-immune animals include high fever, coughing and nasal discharge. It is rarely fatal, though it can lead to complications including pneumonia and some horses can take several weeks, or even months, to recover fully from an infection. An outbreak in New South Wales in 2007 resulted in the closure of Sydney's racetracks from late August until early December, although this was in an unvaccinated racehorse population.
Equine influenza can take up to three days of incubation before symptoms are present, so news of whether racing can return on Wednesday will not come until Monday, sparking widespread fears that the Cheltenham Festival next month is in danger.
"We have a team of six vets taking nasal swabs off the 150 horses here", said the Festival's all-time leading trainer, who is based at Lambourn in Berkshire.More news: Jason Day, Phil Mickelson among early leaders at Pebble Beach Pro
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"The action to cancel racing has been viewed as necessary in order to restrict, as far as possible, the risk of further spread of the disease", the BHA said.
The Animal Health Trust has already identified seven cases in domestically-owned horses in a month in Yorkshire, Essex, Suffolk, Cheshire, Derbyshire and Lincolnshire.
"It takes about three days or so for a horse to start to display symptoms of influenza, so if a horse has shared air space with an infected horse it can take a bit of time to work out if they themselves are now infected".
"The worst part of it is that we are starting to miss races that were part of the horses" preparation, ' he added.
"When new horses arrive at our yard we try as much as possible to keep them separate, but at this stage can not know if the infection came from recent arrivals or from horses returning from racing".
Whilst the infected horses had not been racing this week, McCain has had runners at Wolverhampton, Ayr and Ludlow.
"They stop being contagious once they have recovered, and like with most other species the influenza plays itself out in about three weeks although seriously affected horses may take longer to recover or be left with permanent damage to their lungs".