Those same tribal people you're talking about who "hunt and fish" also have parasites from the fish and meat they eat.
If we want to talk about "natural man", let's talk about early human cannibalism. Genetic markers found all over the world show that we developed a gene early on to protect us from brain diseases caused by eating human flesh. Evidence from pre-historic human skeletons indicate that we would even crack the bones of the dead to suck out the marrow. (http://news.nationalgeographic.com/n..._cannibal.html)