Syphilis appeared in Europe in 1493, and it's widely believed the Columbus crew brought it back from America, though last I heard it's not considered 100% prove

Syphilis appeared in Europe in 1493, and it's widely believed the Columbus crew brought it back from America, though last I heard it's not considered 100% proven. The Old World had bigger cities and more domesticated animals, which promotes epidemics. I also assume the fact the our species is indigenous to Africa means that's where our natural predators have had vastly longer time to evolve.