The devastation that the disease's carried by European's had on Native Americans is commonly discussed, but what about the reverse? Were any diseases carried back across the ocean to Europe?

The truth is that the Pre-Columbian Americas was almost disease-free paradise compared to the Old World, which explains why so few, if any, diseases went back the other way.

Due to relatively smaller population density, lack of interaction between population centers (the Andean and Mesoamerican civilizations seem completely unaware of each other) and most importantly the far smaller level of interactions with livestocks (the amount of domesticated animals is much smaller and on a much smaller scale in America), diseases were far less common and far less deadly in the New World.

When the English first arrived in NA, they always remarked at how tall, healthy and fair-skinned the natives were. That's because the English were starved and scarred by years of disease (like smallpox) in comparison.

Now we think of the South American jungles as fetid, deadly cesspools of disease, but nearly all those diseases were introduced by the Columbian Exchange; early Spanish explorers described huge cities and numerous people in the Amazon, but now there's only malaria, yellow fever and the rest of the lot.

Based on what we know, the average member of the pre-Columbian agricultrual society probably lead more comfortable, more plentiful and less diseased lives than their Eurasian counterparts, assuming weather conditions were good as many American societies lived in very extreme environments. Unfortunately, there was a huge cost to that comfort.