When Christopher Columbus and subsequent Europeans made it to the Americas, they brought with them diseases, such as small pox that devastated the native populations.

Why does there seem to be no record of those same disease being brought over by the vikings who arrived centuries earlier? I understand that they did not have as much contact with as many peoples and were not present over nearly as large of a geographic area. However, it seems like there would be records/indications of plague in the North East that might have spread outwards to some degree.

The question seems to also apply to the theory/hypothesis that Chinese explorers might have landed on the Pacific Costs of the Americas. (Although if they didn't that wold explain why there were no accompanying diseases.)