The Minister for Agriculture expressed confidence that the outbreak of foot-and-mouth disease in Co Louth could be contained.
"It is in the Cooley peninsula, which is in a self-contained region. The farm in question is in the existing surveillance zone and is only a couple of miles from Meigh. We are regarding the outbreak as a secondary outbreak within the existing surveillance zone."
Mr Walsh described the outbreak as "a major disappointment" given the intensity of efforts of all sections of society and by members of the House.
"The flock in question had been examined on a number of occasions because it was in the surveillance zone. It was examined as late as last Friday and last Tuesday.
"On all previous occasions, it was found to be without symptoms. It is clear from the experience emerging from the UK that this disease is difficult to detect, particularly in sheep. Consequently, it is my intention to proceed with an aggressive strategic slaughter of flocks in the region."
He said that on Wednesday controls were intensified in the region and animal movements in Co Louth were stopped on a precautionary basis.
"I also established an extended protection zone, and I have now served an order extending the existing surveillance zone and protection zone around this farm.
"The European Commission and the relevant veterinary authorities have been informed in the last half-hour."
As an initial step, Mr Walsh said, he had decided that the ban on exports from Ireland of susceptible live animals would be retained and that exports of animal products would be temporarily suspended. The matter would be discussed in the standing veterinary committee of the EU today.
"We will seek to ensure that the EU restrictions will be imposed on a regional basis, as was the case relating to France."
The Fine Gael spokesman on agriculture, Mr Alan Dukes, pledged his party's support to the Minister and the various officers and officials who had worked so hard to try to prevent the spread of the disease.
"We will give unquestioning support to measures that will help, but where we see deficiencies we will expose them. Where we can suggest improvements, we will make them."
Mr Dukes said the initial priority must be to contain the outbreak. "It is disappointing to discover that it is a secondary outbreak within an existing exclusion zone. We need to know, as quickly as possible, how it has spread that far.
"We must find the reason and eradicate it. It is even more important that the new and extended exclusion zone, which the Minister has set up, is made as watertight and impenetrable as possible. That will require substantial assistance from the community around the zone and from others."
Mr Dukes said there were herds of deer in the Cooley peninsula. "They are susceptible animals and are capable of spreading the disease. We must implement whatever measures are required to prevent any further spread."
The Labour spokesman on agriculture, Mr Willie Penrose, said it was a day they hoped would never arise, but they had been apprehensive that a case would be confirmed at some stage.
"This is not an occasion for anything other than a concerted unified effort and this must be espoused in the chamber. The public would expect nothing less.
"It is not a day for drawing conclusions either. The two most important issues are the need to identify the source of the infection and the need to put containment measures in place to prevent spread of the disease."
Mr Trevor Sargent (Green Party, Dublin North) said the disease must be stamped out quickly. "I am informed by people in the tourism industry that some £200 million has been lost to date and, as of yesterday, a further £300 million was written off. This outbreak will cause further losses."
Mr Joe Higgins (Socialist Party, Dublin West) said the airborne virus was spread in the wind, which made it a real wild card. "If it were to spread here, I am not convinced that the scorched earth policy of killing and burning every animal in sight should continue to apply without a major debate."
Mr Caoimhghin O Caolain (SF, Cavan-Monaghan) said the immediate question in the minds of many was what effect it would have on the individual schedules of ordinary people and the wider community.
Later, at Question Time, the Fine Gael spokesman on foreign affairs, Mr Jim O'Keeffe, said there seemed to be a different approach in dealing with the problem in Britain. The expert hired by the British authorities had now predicted that the outbreak there would be worse than the 1967 crisis and would not peak until May.
"I do not want to be anti-British about this, but we absolutely have to drive it home to them that we demand the imposition of measures which will guarantee, as far as possible, that there will be no further spread of the disease over to Ireland from Britain."
The Minister for Foreign Affairs, Mr Cowen, said those points would be made to the British authorities. He had been concerned, he said, that the spread of the disease would not peak in Britain until May.
The Department of Agriculture was dealing bilaterally with the British authorities on the issue, he added.