Picking up a puppy and raising it through adulthood can be a wondrously fulfilling adventure for you and your family. Dogs, however, can pick up zoonotic protozoa (such as Giardia and Coccidia ) from puddles, standing water, the ground, their own mother, sniffing feces of another dog, and even from well water. Certain zoonotic worms can also be picked up in some of these same ways. These microbes take up residence in your pet's intestinal tract. Some puppies and dogs develop an immunity to these organisms without treatment with medications. Many pups and dogs show no symptoms of the microbes' presence, and can even test negative for giardiasis or coccidiosis unless they are stressed (e.g., after moving to new surroundings ).
The most common avenue of transmission of these microorganisms to people is by putting something in your mouth that has somehow come in contact with an infected pet's stool. The occurrence of this is extremely rare and, to date, we know of no one who has ever contracted any of these protozoa or other parasites from their pets. Ideally, the easiest way to help prevent your family members from becoming infected is by ensuring that they always wash their hands thoroughly with soap and water after handling their pet and/or cleaning up after it. However, this is only the case if a puppy or dog has tested positive for the presence of any intestinal parasites or protozoa.
The New York State Dept. of Agriculture (as well as most vets) does not consider the mere presence of intestinal parasites (e.g., round worms, tape worms ) or protozoa to be grounds for declaring a dog to be unfit for sale. We routinely medicate our puppies and adult dogs for all such parasites.