It's fashionable to state that Europeans introduced a host of ills such as syphilis, gonorrhea, and smallpox to the otherwise pristinely healthy inhabitants of the New World, but it turns out that lice were here before Columbus-- LONG before Columbus, in fact:
"The two laboratories' DNA test results were identical, the researchers said. They showed that people in the 11th-century Americas already had the prevalent type A strain of lice."
Read the whole story in the Minneapolis Star-Tribune:
BTW: Wouldn't it be interesting (and VERY MUCH ironic) if research discovers that route of transmittal of some infectious diseases was NEW WORLD-->OLD WORLD and not vice versa?