Disease requires mass concentration of people which was less common in America. They did transfer syphilis to Europe though.

Basically, and I'm generalizing but still, all those diseases that Europeans brought over to the Americas came from domesticated European animals. On the other hand there weren't really domesticated animals in the Americas (lamas but barely). So there weren't really epidemic diseases in the Americas to infect Europeans.

This one fact basically explains the entirety of the history between these two hemispheres.

Yeah, Europeans caught syphilis from indigenous Americans, and without any existing immunity to it there was a genuinely terrifying pandemic in Europe with worse symptoms than present-day forms of the disease (and no penicillin to treat it).

But indigenous Americans caught smallpox, measles, influenza, and typhus from Europeans, so it really wasn't a fair exchange.

It’s cause of how European agriculture worked and how they essentially helped create new pathogens.

European medieval peasants were just soooo filthy