It's sort of hard to know the full extent of the damage that was done to the Native American population by the diseases that the Europeans introduced. The big problem there is that the diseases spread a lot faster than the European explorers did, so by the time they got somewhere, large portions of the native population may have already been wiped out without ever coming into direct contact with the Europeans. It's estimated that as much as 90% of the native population may have died from diseases that were introduced by the European explorers.