I heard a long time ago that dogs (another omnivore, like ourselves) have stomach acid 7 times stronger than ours, which effectively kills and digests most of the pathogens/parasites they eat.
I have no cite for this and am too lazy to wade through all the info available, so I ask you veterinary Dopers: is it true?
I just did a quick search and found a page you might be interested in reading here
It relates how dogs are carnivores, not really omnivores, and have digestive tracts and higher concentrations of stomach acid to kill more bacteria and break down proteins. They also lack the digestive enzymes like amylase in their saliva to predigest carbs, and have a harder time with them than a true omnivore such as ourselves. The relevant parts of the page start in the 6th paragraph.