Historians know that there was at least one Viking settlement in America; it is likely that there were more settlements and many small expeditions to North America over a few hundred years which may have reached as far as Maine. There is also evidence of Viking contact with native Americans.
If there really was this much Viking contact with America; why didn't domesticated European animals spread to America and why wasn't there a huge epidemic which wiped out much of the population like when the Spanish arrived?
The Norse settlements in North America we small, remote, and (in a historical sense) short-lived. In contrast, the voyages of Columbus kicked off a period of interaction between Americans and Afro-Eurasians which involved thousands of the latter arriving in short order to regions densely populated by the former.
The Columbian Exchange was not instantaneous, it took generations for the integration we now take as commonplace to occur. This applies as much to potatoes as it does to smallpox. The idea that contact with Europeans immediately led to epidemics among Americans is simply wrongheaded and false. Disease hosts/vectors, have incubation times, infectious periods, and all manner of other biological facts are limiting factors in their spread. Smallpox did not arrive in the Americas until 1517, a decade after Columbus had died. It would be more than a decade until measles arrived in the Americas.
All this is moot with regards to your question though, as none of the pathogens associated with epidemics in the Americas had even reached Iceland, let alone Greenland, at the time of Norse settlement. The Norse groups that settled in North America were already an offshoot of an offshoot of the main European population, insulated from the mainland such that diseases introduced to Iceland would have similarly devastating effects (on a biological scale) as were seen in the Americas.