An outbreak of equine influenza in Japan has caused sufficient concern to cancel racing in the country through this weekend, according to the Japan Racing Association (JRA). At some tracks, the ban has been extended to August 23.

Also at risk are some of Japan’s top international stakes horses, who will be affected by travel bans imposed by other countries. Delta Blues was scheduled to travel to Australia as defender of the Melbourne Cup.

Even worse news is that, according to the Sydney Morning Herald, leading turf horse Meisho Samson has tested positive and will not be traveling to France to run in L’Arc de Triomphe.

The last time that flu forced the JRA to cancel races was in 1971, when racetracks were shut for nine weeks after 1800 of the JRA’s 7000 Thoroughbreds became ill. Since then, the JRA has required all horses to be vaccinated.

It is not clear from reports exactly what strain of flu has hit the Japanese horses. JRA has curtailed all transport of horses between farms and training centers, cutting many horses off from the opportunity to train.