Hi, fyi there are a couple of comprehensive answers in the FAQ

#Disease in the Americas

##Did the Norse carry European diseases to the Americas?

If the Vikings visited North America before 1492, was there any evidence that any population was wiped out (partially or otherwise) by small pox? by /u/Reedstilt

One of the main reasons Europeans were so utterly victorious against Native Americans was the introduction of diseases, that decimated the population. Why did the Norsemen of Vinland not bring diseases that carried the same effect? by /u/anthropology_nerd