The Protozoan Problems

Protozoal parasites are small single-cell organisms that can't exist very well outside their given host or a specialized environment. Many of the common protozoa we may find in our dogs can also affect people. Good hygiene is very important in dealing with these and any parasites. Sharing love with our dogs is one thing — sharing parasites of any kind is another!

The best way to diagnose protozoal infections is with a fresh fecal sample. In this case, your veterinarian will take a small sample directly from your dog's rectum. The sample will be mixed with saline and examined under a microscope for protozoa actively moving around. A regular fecal test would kill the protozoa and make them virtually impossible to detect.


Giardia is sometimes called beaver fever, but beavers shouldn't bear the blame for this one. This protozoal parasite is quite hardy and can exist for long periods of time in a wet environment. Streams and ponds are its favorite sites. Drinking infected water may lead to severe diarrhea, sometimes with blood or mucus. The cysts are then passed into the feces and may contaminate other bodies of water. There are treatments for Giardia, but it can be difficult to diagnose. Your veterinarian may need to check multiple fecal samples, including some fresh ones taken on a rectal exam. This parasite can be spread to people as well, so you and your dog should both avoid drinking water from streams or ponds in areas where this parasite is known to exist. There is now a vaccine for dogs in epidemic areas.


Coccidia are well-known intestinal protozoa that can infect dogs. There are many species, but virtually all work the same way. Dogs that live in a less-than-clean environment, especially puppies, may ingest cysts through contaminated food or fecal material. Dogs with Coccidia may show diarrhea, sometimes with blood. In puppies this can be a debilitating disease. People are resistant, but kennel areas still need to be kept immaculately clean to prevent puppies picking up this protozoa. Diagnosis is fairly easy with fecal checks.

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