Transmission of parasites can happen from a number of sources, these are called Vectors. Typically protozoa are water borne but this can also mean that produce can serve as vectors. With globalization, this can make transmission easy as well. I never consume raw fruits or vegetables without using some sanitizing solution. Make sure you practice safe food handling as well.
Animals and humans can serve as vectors as well. Pathogens transmitted via animals are called zoonotic infections. Parasites can be sexually transmitted.
There was an infomercial some time ago that talked about toothbrushes and they were pitching a steam sanitizer for your toothbrushes with the idea that fecal material can land on the toothbrush. They proposed that when brushing your teeth that you were actually creating microscopic scarring in the gums that allowed pathogens to embed in the gums.
Using a mouth rinse that has antimicrobial properties is a good idea following brushing. Using hydrogen peroxide to sanitize the brushes makes sense as well.
I host a forum devoted to protozoa parasites at pptu.lefora.com and have done extensive research. You have to use a multi prong approach to eliminate them and not the typical parasite products like a Black-Walnut
type of product. Protozoa are hardy meaning you have to keep constant pressure on them.
Caprylic acid can be effective as is neem, graviola, black seed, peppercorns. Hemp oil (Nutiva) and goldenseal leaf (not root) have properties that can eliminate resistance. Check with your doctor.