The illness pirates get when they have unkempt peg legs. This is often a gross and unsightly infection surrounding the area where the peg meets the leg. Doctors have never seen this because pirates are like outlaws and Chuck Norris, and don't need doctors. It should clear up in a couple days, if not, then the infected person will die.
Arg, ye got yerself a bad case of Peggle. Git off me vessle 'fore it spreads! Arg.