I'm just saying that every time societies have centuries long cooling periods diseases become very much a problem. To think the Americas are ever an exception is to think of the Americas as some kind of fairy tale.
Rapant diseases was a normal part of life during the Little Ice Age (roughly AD 1300-1800's, particularly 1500's to 1800's) and during the Dark Age cooling period (AD 300 to 1900) and the Greek Dark Age (1000 BC to 700-ish BC). It's well documented history -- at least in civilizations that had written history (hint: the indigenous Americans didn't write). During the warm periods the diseases go way down and the crop yields go way up.
When the Europeans came, for the first time the Americas had written history, thus this was the first cooling period that rampant diseases could be recorded, unlike in other parts of the world where we have recorded history of horrible plagues during other cooling periods too. It's also no surprise the Europeans came during the Little Ice Age. One of the reasons the King of Spain hired Columbus was because the land route to the far east was virtually impossible to cross the Himalayas during the cooling period, then once land was found in the Americas all of the European countries saw land they could cultivate to offset the low crop yields during the cooling period.
It's also a well known fact (or at least I thought it was LOL) that the indigenous Americans also were struggling with the Little Ice Age. IMHO it's one of the main factors in the intertribal wars. I'm not saying they didn't have other motivations, like revenge wars in the northeast. I'm saying that often the wars were over food or land to raise food --- because crop yields were down here in the Americas during the Little Ice Age like they were in much of Europe, Asia, and sub-Saharan Africa. Life sucked, period. It motivated many tribes/nations of all colors to fight people that we today clump together as one race (when often tribal differences mattered to different races as much as racial differences did).
Basically I'm saying that both the Europeans' first impressions of the Americans and the Americans' first impressions of the Europeans was when both groups saw each other during their worst. Meeting each other during the Little Ice Age was like catching each other when their pants were down -- a horrible first impression. Disease is part of that bad first impression that IMHO is wrongly associated with the Europeans.
Actually the Indians of the Americas did have writing, at least the Aztecs and the Mayas. Their books were burned except a few that still exist in Spanish archives. I just saw an interesting show on PBS about the Maya. Their stone writing still exists as does writing on ceramic objects. I know a lot less about the Inca culture.