Originally Posted by Dragoness

25% of people in the USA have worms. Most of us don't even know it. Because many parasites like the one humans get (pig roundworm) manage to live in our bodies without doing us much harm, they can often go unnoticed.

Some parasites' life cycles cannot be completed without exposure to stomach acid.

Considering how people get to doctors much more often than most animals get to good vets, I think the rate for parasite infestation is higher in animals.