The parasite Giardia often raises concern for both dog and human health. In reality, while it’s a potential problem, it’s probably over-rated (or at least there’s a bit too much paranoia at times). A reasonabe percentage of healthy dogs (probably ~7% in Ontario) are shedding the parasite at any given time, but very few will go on to develop disease. It can cause diarrhea, but only in a small minority of exposed animals, and usually it’s not a big deal. Giardia also a zoonotic pathogen, but as we’ve learned more about this parasite in recent years, it’s becoming clear that pets pose a limited risk to people. Most studies have identified Giardia found in dogs to be dog-specific strains that do not infect people.

Here are some interesting tidbits about Giardia from a few recent papers.

• A study of dogs in southeastern Europe reported that dog-specific assemblages (strains) accounted for all of the Giardia identified (Sommer et al Parasitology Research 2015).
• All Giardia-positive pet dogs in an Italian study also harboured dog-only types (assemblages C and D) (Paoletti et al Parasitology Research 2015).
• The parasite was found in 15% of shelter dogs from northern Italy. All but 1 of the 79 positive dogs had dog-specific strains (Simonato et al Parasitology Research 2015).
• 25% of breeding kennel dogs in a Japanese study were infected with Giardia (Itoh et al Parasitology Research 2015).
• Healthy dogs with Giardia had a different fecal microbiota (bacterial population) than healthy dogs that were Giardia negative (Slapeta et al International Journal of Parasitology Research 2015). Whether that’s cause (i.e. Giardia affected the microbiota) or effect (i.e. an altered microbiota made it easier for Giardia to move in) is now important to figure out.
• A systematic review and meta-analysis came to the (unsurprising) conclusion that Giardia is more common in young animals. It was also more common in dogs and cats with intestinal disease (Bouzid et al Veterinary Parasitology 2015).

Does that mean we should just ignore Giardia? No. It can definitely cause disease in dogs, and sometimes it’s hard to treat. It can also cause disease in people (I spent a couple days in hospital with Giardia many years ago… never did figure out how I got it). It’s important to remain balanced, though. Pets are a minimal to inconsequential source and people shouldn’t freak out if their dog is diagnosed with Giardia. At the same time, it’s a “don’t eat poop” disease, so basic prevention practices are easy.