Europeans had domestic animals (horses, pigs, cows, sheep, dogs, chickens), meaning that they had acquired resistance to the many diseases that animals bring wi

Europeans had domestic animals (horses, pigs, cows, sheep, dogs, chickens), meaning that they had acquired resistance to the many diseases that animals bring with them. The Americas had few animals that were capable of domestication, thus natives did not domesticate animals and did not acquire resistance through close exposure. When Europeans first arrived with their animals, it entailed natives first exposure to these pathogens.