Everyone has some sort of "bug" inside them. You get parasites from food, from other people, walking outside, petting animals, breathing, etc. Diane, I guess you get parasites simply by living your life. You can't escape not getting them.
Some people have more parasites than others. Everyone can have different kinds of parasites. Think of it like this---if a dog can have worms, why can't people?
As far as symptoms, most people don't even know they have them, so they would be no symptoms.