In the old days when Jews decided to not eat pigs, and later Muslims, the pigs went about eating anything they could get. They were often infected with the Trichinella spiralis parasite. If the meat from an infected pig is not cooked well, the parasite will be transmitted to the one eating the meat.
Nowadays, pigs in developed countries are not free ranging, eating garbage, but well-fed with controlled pig food, so they are not infected, and there is no risk.
However, people still get infected in parts of the world where the pigs are not in a controlled environment. The white spots in the X-ray picture below are cysts of the parasite in an infected human.