(CNN) -- Danedream's hopes of becoming the first horse in more than three decades to win the Prix de l'Arc de Triomphe in successive years have been thwarted by a health scare.
The defending champion had to forfeit her place in this year's race after the outbreak of equine infectious anaemia at a racing yard in the German city of Cologne, where Danedream is trained.
Although the infected horse is stabled at a different yard to Danedream, Germany veterinary authorities have placed the entire area on lockdown for three months, meaning the German filly will not be able to make the trip to Paris.
Speaking from his Asterbluete stables in Cologne, Danedream's trainer Peter Schiergen confirmed his horse was fit but that they were 'absolutely shocked' at the news.
"Danedream is safe and well," Schiergen told CNN. "She worked yesterday morning and then came the news that the veterinary office had closed the track for three months.
"The case is not in the yard where Danedream is but at another yard in the area."
Equine infectious anaemia -- also known as swamp fever -- is a disease that is transmitted by bloodsucking insects.
It can be passed from horse to horse through bodily fluids as well as contaminated stable equipment such as syringes and bits and, although fatalities are extremely rare, the disease can cause chronic tiredness as well as recurrent fever and anaemia, sometimes up to several years after the original attack.
After Danedream's Arc success last year, which saw her smash a strong international field to take the course record, the German filly won the King George VI and Queen Elizabeth Stakes at Ascot in July, becoming the first German-trained horse to win Europe's two most prestigious all-age races.
Last month she also successfully defended her title in the Grosser Preis von Baden -- one of Europe's traditional Arc trials.
That run of form had placed Danedream among the favorites for Sunday's renewal at Longchamp, where she would be aiming to emulate Alleged's 1977 and 1978 victories.
She would also have become the first filly to successfully defend the Arc since Corrida in 1937.
The German filly is the latest horse to pull out of Sunday's showpiece event.
Arguably England's best chance in the race, Ed Dunlop's Snow Fairy, has been ruled out for the rest of the season after sustaining a slight injury in her last serious training session, while earlier this year Prix de Diane winner and early Arc favourite Valrya was put down after breaking a leg in a freak training accident.
Aiden O'Brien is expected to make a final decision on 2,000 Guineas and Epsom Derby champion Camelot's participation in the coming days.
The three-year-old, who narrowly missed winning the English Triple Crown when he was beaten in the St Leger, will be certainly be without regular jockey Joseph O'Brien as the teenager is unable to make the required weight.
That leaves the 18-strong field wide open for Japanese Triple Crown winner Orfevre, who is favorite to become the first ever Japanese winner of this race.
Last year's runner-up Shareta and English colt Nathaniel, narrowly beaten by Danedream in the King George, are tipped to be Orfevre's chief rivals.
A huge contingent of traveling Japanese fans and journalists is expected to watch the race at Longchamp Racecourse on Sunday.