It is a highly infectious viral disease in which fever is followed by the development of vesicles or blisters - chiefly in the mouth or on the feet. There are 7 main types of virus, which produce similar symptoms and which can only be differentiated in the laboratory.
Infected animals begin by excreting the virus a few days before signs of the disease develop.
Pigs in particular produce large numbers of virus particles. Airborne spread of the disease takes place readily. The prevailing meteorological conditions and local topography determine the distance that the disease can travel and this may be considerable. For example, circumstantial evidence strongly suggests that the outbreak on the Isle of White in 1981 resulted from the airborne spread of the of the virus from Brittany in northern France. The disease is also spread mechanically by the movement of animals, persons, vehicles and other things, which have been contaminated by the virus.