It also impacted the New South Wales racing and breeding industries for eight months, costing close to a billion Australian dollars to eradicate.
I asked my Talksport2 colleague, racing presenter Lee McKenzie.
That's three additional positives and, most significantly, one of them is Raise A Spark which ran at Ayr on Wednesday. If it can be contained quickly it could be over in a matter of days.
One of Donald McCain's horses, which is infected with equine flu, raced this week. "The biggest worry is how three racehorses were found to be carrying the virus despite being vaccinated against it".
"If you're to ask me again about Cheltenham I hope to be completely definitive then".
The BHA revealed late on Wednesday that all meetings had been cancelled for the following day due to concerns that the disease could spread after three vaccinated horses in an active racing yard tested positive for equine flu.
"We know we're not going to be in a position, given the incubation period of the disease, to make a decision about returning to racing until first thing next week at the very earliest".
Thousands more swabs are expected to be received and tested over the coming days, the BHA added. There is as yet no evidence of widespread infection, however we will continue to monitor this situation closely.
"This is a serious form of flu, which debilitates horses". The welfare of our horses is really paramount above all economics.
The BHA conceded "the full extent of potential exposure is unknown" but is working as fast as possible to gather information about any potential spread of the outbreak.
People outside racing who usually have a punt on the Grand National once a year have noted how fast the sport has closed ranks and shutdown immediately without a hint of objection.
'This is a standard contingency in the event of an infectious disease affecting our horses.
The origin of the infection is unclear, with Cheshire-based McCain - whose late father Ginger trained triple Grand National victor Red Rum - keen to emphasise he would never knowingly have run a potentially infected horse.
North/South racing and transport of horses is unaffected.
The BHA has said it is far too early to say if the showcase meetings at the Cheltenham Festival and Aintree will be affected.