Gardai are investigating the possibility that a rogue livestock dealer or farmer based north of the Border may have released infected or suspect sheep on to the Cooley mountains. It could have been done out of fear of a visit from the authorities.
The possibility of wind-borne infection from the farm in Meigh, Co Armagh, where the first outbreak on the island occurred, is considered unlikely. Direct contact is the main line of inquiry being pursued, Garda sources have confirmed.
"It has to be linked to smuggled sheep somehow," said one experienced sheep farmer, who farms near the Border.
Detectives from the Louth-Meath division with gardai from the National Bureau of Criminal Investigation are working with officials from the Department of Agriculture to trace the movements of all sheep on the Cooley peninsula in recent weeks.
There has been widespread co-operation from the farming community in the peninsula, though it appears increasingly likely that all sheep there - and maybe even all livestock - will be culled.
On Saturday morning gardai carried out a number of searches of premises in Ravensdale but did not find anything to indicate livestock smuggling, it has been confirmed. They did discover two dead sheep whose carcasses had not been disposed of properly, but they are not believed to be linked to the outbreak.
A spokesman for the Department of Agriculture said the investigation into the source of the Louth outbreak would continue until it get to the bottom of it. "We are ruling nothing out and are looking at every possible scenario. Information on any possible source is being followed up," he added.
In the coming days the Department will evaluate whether the cull of animals needs to be extended. Over the weekend members of the Army Rangers Unit, at the request of Duchas, assessed the presence of wild goats in the Cooley Mountains. Their possible culling is under consideration as they are susceptible to foot-and-mouth.
The marksmen in the Rangers Unit are available to carry out the slaughter if sanctioned by the Department.
Yesterday the slaughter of sheep continued at the AIBP plant in Ravensdale. The Department hoped to have competed the slaughter of 13,500 sheep within the 3 km zone by last night.
In Co Meath the Garda investigation, which began after the Meigh outbreak, resulted in four farms being sealed off on Friday night and Saturday morning. They are in Trim, Longwood and Fairyhouse.
"These sheep are suspected of originating in England and may have had contact with the Meigh sheep," a senior garda said.
It is believed these were the sheep referred to by the Northern Ireland Minister of Agriculture, Mrs Brid Rodgers, last week. The haulier, Mr John Walsh, has stated publicly that he was responsible for bringing the Meigh sheep from Carlisle into Northern Ireland.
Samples have been taken from flocks on all four Meath farms and are being tested for the virus. The flocks involved were slaughtered as a precautionary measure.