How do, scientifically speaking, people like Indians have such high resistances?

There's been numerous reports of people trying Indian street-food, being hospitalized in near death situations. Yet Indians eat it every day.

If any western person tried any of the stuff Indians do, like bathing in the corpse and shit infested Ganges, or eating cowshit, they would most likely end up severely ill.

How can Indians do this stuff with no ill effect?