A garda investigation is under way to discover how the sheep contracted the disease. It is being led by Chief Supt Michael Finnegan of the Louth/Meath division in conjunction with the Department of Agriculture.
"We have begun a complete investigation to try and establish the exact movements of the sheep over the last couple of months.
"We want to account for every single sheep and establish whether they had any contact with the sheep at Meigh or with any other place the sheep at Meigh went to," he confirmed last night.
Farming representatives and local gardai said Mr Michael Rice and his family were extremely well regarded in the farming world and there was no suggestion that any of the animals involved had been illegally imported.
Initial Garda inquiries have established that all the sheep concerned originated in the Republic. Gardai acted swiftly in erecting checkpoints with officials from the Department. They put a de facto exclusion zone, covering a 10-kilometre radius of the farm, into place on Wednesday night, more than 12 hours before the results were announced.
There are now an additional 13 checkpoints stretching from the mouth of the river Fane, four miles south of Dundalk, across the main Dublin-Belfast road and inland towards the Louth border with Monaghan.
In the three-mile exclusion zone, which takes in a sizeable area of the Cooley Peninsula, Chief Supt Finnegan said: "There will be absolutely no movement of any animals." There will be no movement of people in or out of farms and the movement of people within the zone will be closely monitored by gardai and all restrictions will be strictly enforced.
All commercial deliveries of farm produce to supermarkets, hotels and other outlets will only be allowed if permits have been issued by the Department. They can only be issued at its centre in the Ballymascanlon Hotel.
However, people in Dundalk town have been told that, apart from traffic delays, there should not be an immediate impact on their lives.