Horse racing in Britain has been canceled until Wednesday at the earliest over an outbreak of equine flu. (Joe Giddens/PA/Associated Press)

British horse racing officials have canceled all of the country’s races until at least next week because of an outbreak of equine influenza.

Three race horses tested positive for the disease this week even though they were vaccinated, and horses from the same racing yard competed Wednesday, sparking fears the highly contagious illness could spread. British veterinary officials have been in contact with more than 50 trainers to test the nation’s thoroughbred racers, but the disease can take three days to exhibit symptoms, leaving authorities unable to judge whether it is safe to resume competition until at least Sunday.

That would allow the British Horseracing Authority on Monday to announce the reopening of races for Wednesday. Tuesday, trainers could make “declarations,” or decide which horse would run at which race, with 24 hours notice.

“This precautionary approach is intended to ensure we put the health of the horse population and control of the virus first, and avoid any unnecessary risk that might come from returning to racing too quickly,” the Authority said in a news release. “We appreciate the impact that this may have on the sport commercially, but disease control in order to mitigate the risk of further disruption to the sport — and safeguard the health and welfare of our horses — must be a priority.”

All British race horses are required to be vaccinated against equine influenza, but not mules, donkeys and non-racing horses, for whom the disease can cause serious health problems. Among vaccinated horses, the effects are more mild.

Equine influenza causes symptoms similar to the flu in humans, including fever, respiratory congestion, cough and nasal discharge, according to the American Association of Equine Practitioners.

“It’s very similar to human flu; the symptoms are the same, and the horses feel the same,” British trainer Seamus Mullins told the BBC. “You get a high temperature, a nasal discharge, and eventually you get coughing and the horses feel rough. It’s similar to humans — but they get over it.”

The disease is airborne and spreads between horses in proximity, according to the AAEP, but can also be transmitted through contact with humans and equipment that have not been properly disinfected. It is harmless to people.

But the outbreak comes at one of the worst possible points of the season for the British racing industry. Cheltenham Festival, one of the largest meetings of the National Hunt steeplechase racing circuit, is almost a month away, and breeding season is soon to begin.

The “Super Saturday” meeting at Newbury Racecourse has already been scrapped.

“If it was a long-term stoppage it would hit racing very, very hard both with the day-to-day training of the horses, but more importantly it would financially hit the industry very, very hard,” Mullins, the trainer, said. “Every day without racing is a loss on income for everybody, from the stable lads in the yard to the jockeys, trainers, owners, bookmakers, racecourses, it would be very, very serious.”

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