Precautionary culls were under way yesterday on a fourth suspect cattle farm in Ardboe, Co Tyrone, and on a sheep holding in Ballintoy, Co Antrim.
Vets identified clear clinical signs of foot-and-mouth disease in animals at both locations, and a spokesman for the North's Department of Agriculture admitted confirmation of two more outbreaks could be imminent.
"The only consolation is that we have linked both to the previous cases at Ardboe and Cushendall. The last thing we want now is for an outbreak to occur in a completely different area," he said.
Six weeks after the first outbreak was confirmed on a farm in Meigh, Co Armagh, following the illegal harbouring of sheep imported from Carlisle, the North was daring to think it might have escaped foot-and-mouth.
However, these hopes plummeted when a positive result was returned from Pirbright on a herd of pedigree cattle in Ardboe last weekend. A third confirmed case followed swiftly in Cushendall, 40 miles away.
Mr Joe McDonald, of the Ulster Farmers' Union, admitted yesterday the two outbreaks had left everyone "scratching their heads".
He said it had now been accepted that the virus had been present in the North's sheep flocks for some time, and farmers had been living in "a fool's paradise", believing it was contained in south Armagh.
"It is now thought the missing pieces of the jigsaw are imported sheep that instead of going for slaughter found their way to farms," said Mr McDonald.
Farming sources have told how a number of marts in the north-west region of Northern Ireland were recently used by farmers looking for cheap replacement breeding stock among imported sheep, also from Carlisle.
The good market price of lamb, attributable to the BSE crisis in Europe, enticed many to sell hoggets originally to be used to replace older ewes.
"Farmers sold the hoggets into the food chain for £70 and went to these markets to buy replacement sheep for £35, to keep up their numbers for EU premiums," said one source.
When the foot-and-mouth crisis broke on February 21st these farmers, mainly from the Sperrins and the Glens of Antrim, the most densely populated area of sheep farming in Europe, were without proper documentation and reluctant to come forward to the Department.
The North's chief veterinary officer, Dr Bob McCracken, believes a programme of serology testing on sheep from each sheep flock is the only way of getting ahead of the disease. Testing will begin in 10 km zones in the Glens and Sperrins this weekend before widening across the North.
By the end of next week the Department of Agriculture hopes to test 10,000 blood samples a day for antibodies which show in sheep one week after infection. A positive result will mean a precautionary cull at the location. Department investigators have already traced all sheep imported from Britain from February 1st to 21st. One flock of 99 and another of 19 are still alive and under observation.
Officials have now returned to January records, concentrating on movements through three markets in the north-west. Three men were interviewed this week about the illegal distribution of imported sheep.
Mr Micheal McCoy, of the Northern Ireland Agricultural Producers' Association, who is a south Armagh farmer, said the all-clear announcement for serology test results in the area proved the farmers had acted responsibly during the outbreak at Meigh.
"Other areas didn't take it quite as seriously as we did. The recent outbreaks have shown a satisfactory effort was not made, but that's history now and we just have to get on with it."
Mr McDonald, of the UFU, said the results from south Armagh showed the disease was not yet "rampant", and there was still a possibility of containing it.
"With the detective work and the results of the serology we'll put the picture together. Until then, fortress farming is the name of the game," he said.