Why was the exchange of nasty germs between the Americas and Europe so unequal?

What were a few more nasty germs?

Please, no more about nasty germs.

It smells a little like lemon-scented hog manure, but it does a dandy job of getting rid of those nasty germs.

This handy bathroom gadget will help you keep your toothbrush spick and span, and free of any nasty germs that may be lurking in there.