I agree that they have certain defenses. But human, cat, dog, chicken, deer, etc...if you eat a parasitic worm egg...you will probably get worms. Thank you for mentioning the algae bloom. It is a real problem that I think most people are unaware of.Not always. I worked for a vet for 15 years, and we treated many dogs and also cats, for giardiasis, coccicidiosis, and general stomach upsets from eating or drinking from unclean sources. Yes, dogs drink from the toilet, and their systems do handle bacteria better than ours do.They also get sick from bacteria. They are also dying from Bluegreen algae blooms in lakes. So do wild animals, BTW.