I think it was originally hoof-and-mouth, because it only had to do with animals, but them when humans got sick they decided that foot-and-mouth would be more apposite because humans don't have hooves.

In an ABC new bulletin, Peter Jennings explained it as a UK/US variant thing - "hoof-and-mouth" = N.America, "foot-and-mouth" = everyone else. Also, for what it's worth, there is apparently only one recorded case of a human ever getting sick from the disease. Addendum After reading Bridget's post, I thought I had better expand on the previous statement. A BBC bulletin said that in the UK, there has only ever been one recorded case of a human geting sick from F&M.