Racing will not resume until at least Wednesday as authorities seek a “safe, measured, responsible way” to start up again.
The strain of equine flu which has halted UK horse racing is the same one which shut down racing in Australia for three months in 2007, affecting more than 10,000 horses.
It is a strain endemic to North and South America known as Florida Clade 1, Sky sources have established.
The British Horseracing Authority’s (BHA) chief regulatory officer, Brant Dunshea, told Sky News: “We have seen in non-thoroughbred horses that have presented with the illness prior to this event that it has involved that particular strain.
“‘We are working at the moment with the Animal Health Trust to confirm that.”
The BHA said it was “planning for a variety of scenarios under which racing may recommence”, adding that it was “planning as normal for the Cheltenham Festival”.
It is meeting on Monday to discuss the “programme of upcoming race meetings”.
Discussing the outbreak in Australia, Sky News correspondent Enda Brady said horses there were “not vaccinated at the time, and the virus was completely alien to that continent”.
He added that vaccinated thoroughbreds in Britain have a “measure of protection” against it.
A strain known as Clade 2 is endemic to Europe, the BHA said.
Mr Dunshea, who was working in Australia at the time, said racing was stopped for a week in Melbourne, and for “much longer” in other parts of the country.
Since a number of UK horses tested positive for equine flu earlier this week, 2,100 have now been swabbed nationwide. More than 700 of those swabs have been tested and reported on.
Races were initially called off on Thursday after three horses from Donald McCain’s yard in Cheshire were found to be unwell.
Mr Dunshea said that managing the desire of the public to go racing, and the welfare of the horses, was a “challenge” and a “fine balance”.
He said: “Of course we all want to get back racing as quickly as we can, and we will do that.
“But we will do that in a safe, measured, responsible way as soon as is possible.”
Mr Dunshea said it was the right decision to close racing down, adding that the BHA was gathering as much information as it could to understand the scale of the problem, and would “make decisions based on the science and expert advice”.
Equine flu is a highly contagious viral pathogen which causes respiratory disease.
Outbreaks of the condition often occur when susceptible horses are congregated and housed in close contact with each other.
Symptoms include fever, loss of appetite, lethargy, a runny nose, swollen neck glands and a cough.