The farming industry has called for the effective sealing of the Border and an investigation into how the second case of foot-and-mouth in the North occurred. The tourism industry has described the news as a "major setback".
The IFA president, Mr Tom Parlon, said last night's news was "the last thing I was expecting".
He believed it was a "fresh outbreak" (probably unrelated to the one at Meigh in Co Armagh), which happened "out of the blue".
As "the major reservoir" of the disease was the UK, he concluded it must have come from there, and recently. Mr Parlon also called for the Border to be effectively sealed. It had "to be reinvented as a barrier at the moment, which is unfortunate considering how things have been going on the island as a whole". The latest outbreak had to be "contained where it is", he said.
The ICMSA president, Mr Pat O'Rourke, said the new outbreak was "a devastating blow at a time when there was a sense of confidence that we were going to win the war against foot-and-mouth".
The fact that this latest outbreak was in a dairy herd was "alarming. It has either jumped a species or a new infection has come into Ireland", he said.
He advised farmers of the need to mount a fortress operation once more as this was "a full emergency again". They must immediately move to protect their own farms, he said.
He had no doubt we were going to see a redoubling of efforts along the Border to keep the disease out and every attempt to contain it within Northern Ireland.
The news could not have come at a worse time for the tourism industry, according to industry sources.
Mr Brendan Leahy, Chief Executive of the Irish Tourism Industry Confederation said the timing was "awful".
"This is a major setback," he said. "We in the industry had just last week begun a £6 million `reassurance' campaign in North America and Britain, telling people it was safe to come to Ireland on holiday, that the restrictions were easing."
The tourism industry has already seen losses estimated at £300 million as a result of the crisis, he said, and was facing losses this year of £500 million if the crisis was not brought to an end.
"It comes just after Easter when a lot of small businesses are opening for the season," said Mr Leahy.
"There are numerous small businesses in more remote regions absolutely dependent on tourism. Many have already deferred decisions about taking on staff and there is no doubt that if we have to go back to the restrictions there were at the beginning of the crisis we will see businesses closing."
He went on however, that the industry would "go along with" any restriction imposed as a result of the latest outbreak.
Mr John Power, chief executive of the Irish Hotel Federation, said it was "obviously upsetting and disappointing" news.
"I would hope that the easing of restrictions on `minimum risk' activities would not be reversed or pulled back. And yes, I would be worried about the effect the news could have on the North American market. There are going to be difficulties - there is no getting away from that," he said.
A spokesman for the Minister for Tourism, Sport and Recreation last night said Dr McDaid had sympathised with his Northern colleagues "on this setback".
In the North they had been successful in containing the outbreak so far and he hoped they would overcome "this disappointing development should it be confirmed".