If a disease native to the Americas emerged and became endemic, it would have infected Europeans when they arrived. There’s a good CGP Grey video on this called

If a disease native to the Americas emerged and became endemic, it would have infected Europeans when they arrived. There’s a good CGP Grey video on this called Americapox. https://m.youtube.com/watch?v=JEYh5WACqEk https://m.youtube.com/watch?v=JEYh5WACqEk