The investigation of the foot-and-mouth outbreak in Co Louth is looking at the possibility of the airborne spread of the virus - as well as the more usual route of contact with infected livestock.
Airborne spread depends on climactic conditions. Veterinary experts say the virus may spread over 10 kilometres on land under favourable conditions of high humidity and moderate windspeed.
Strong winds disperse the virus but it can spread over a distance of 200 kilometres across water, as there is less turbulence. Met Eireann has said that between February 28th and yesterday, there were approximately five days with north to north-easterly winds, as well as two or three days with light variable northerly winds. There were also six to eight days with easterly winds, but there is only a "very slight chance" of the virus travelling to the Republic from Britain in its view.
Airborne spread occurs particularly where pigs are shedding the virus as they shed up to 3,000 times more virus than cattle or sheep, explained Dr Bob Ward of Liverpool University's Veterinary School. Downwind from these pigs, cattle and sheep, who are very susceptible to the virus, are infected, he added.
Mountains, trees and birds can also disperse the virus as it travels through the air. "In the 1967 outbreak in the UK, it was widely believed, but not proven, that starlings contributed to the spread of the disease," said Dr Ward.