Once a case of foot-and-mouth disease has been confirmed, there is a high risk the virus will spread to other locations.
But a number of variables make it difficult to predict exactly how it will spread, and how an outbreak might be contained.
Such variables include the type and number of animals infected and how they were dispersed, said Prof P.J. Quinn, professor of veterinary microbiology and parasitology in the faculty of veterinary medicine at University College Dublin.
The pattern of how the animals are dispersed is vital, said Prof Quinn.
If an infected animal was transported directly from a farm in England to a farm in, for example, north Dublin, the disease is easier to contain than if the animal was taken to a mart in the State where it mixed with other animals before moving to the farm.
The disease will spread much more rapidly when an infected animal mixes with other animals - and the original source of the infection will be harder to trace, he said.
The virus which causes the disease can travel through the air for over 100 kilometres, but this depends on prevailing weather conditions.
Ideal conditions for the airborne spread of the virus are high humidity, low temperature and a moderate wind to carry a concentration of the virus.
Landscape features are also a factor. A concentration of the virus could travel over a relatively flat landscape; trees and mountains could disperse it. The virus can also travel over a body of water.
Infected pigs are the most potent source of the airborne virus, as they shed large amounts of it, said Prof Quinn.
Another important factor is when an animal might have been infected. An animal infected a few days ago, for example, may be incubating the disease but not showing clinical signs: lesions on the lips, tongue and feet; high temperature, lameness, and a depressed state.
During this incubation time, it may be shedding the virus, said Prof Quinn.
He said it was difficult to design a method of control if the locations of all infected animals were not known.
Once a case has been confirmed, a number of measures must be immediately introduced to stop the spread of the virus, he said. As the main method of virus transfer is through animal contact, there must, firstly, be an "absolute embargo" on the movement of all animals within a 20km radius of the confirmed outbreak. Secondly, slaughter of animals must begin immediately, once there has been laboratory confirmation of the disease's presence.
And, thirdly, all premises, vehicles, clothes, and organic matter in the area must be disinfected. All hay must be burned, and the area of the outbreak must be depopulated of animals for several months. Prof Quinn also said foot-and-mouth is an exotic disease in the State, given that it has not been here since 1941. Consequently, veterinary surgeons who have graduated since then would not have seen a case - unless they had worked abroad.
If a vet recognises symptoms of what may be foot-and-mouth disease, Prof Quinn said they must immediately inform the Department of Agriculture and wait on the premises until an inspector arrives.