Can Dogs Develop Immunity to Giardia?
My 5 and 1/2 month old dog has been tested for Giardia in the last two months. When or if she gets better, will she have developed some immunity to the disease or will she contract it again as soon as we take her outside?
San Francisco Potrero Hill, CA
Giardia is one of the most nebulous bogeymen in veterinary medicine. Few vets agree about the degree of pathology (that's a fancy way of saying sickness) that Giardia causes. Add in experts' differing opinions on the transmissibility of canine Giardia to humans and you have a recipe for a quagmire.
Giardia is a one-celled microscopic intestinal parasite. It is linked to diarrhea in dogs. Some vets think it causes diarrhea. However, many dogs that are infected with Giardia don't develop any symptoms or illness whatsoever. Many experts therefore feel that the parasite does little more than exacerbate pre-existing intestinal disorders. Some rogue veterinarians don't think Giardia causes disease at all.
In other words, these experts feel that an infected dog may be fine until she breaks into the trash and gives herself food poisoning. The parasites may then spring into action and make the already certain case of diarrhea worse.
Here's the bad news: it appears that some dogs never clear Giardia. But there is good news: a Giardia infected dog that isn't sick doesn't have a problem.
Dogs that test positive for Giardia, then test negative, and then test positive again probably aren't contracting the disease anew. Most likely they were infected the whole time and they simply weren't shedding organisms and certain proteins (called antigens) produced by the organisms when they tested negative.
My recommendation is to worry less about test results and worry more about how your dog feels. If she isn't sick, let her lead a normal life and back off on the testing. Be especially wary of Giardia-specific tests called antigen tests. Focus instead on general stool tests that look for actual Giardia organisms microscopically.
If the organisms are in her stool your dog should be treated. If they aren't, and if she doesn't have diarrhea or any other symptoms, then I have a hard time justifying further treatments--or tests.
And by all means, let her get out to enjoy that nice Potrero Hill weather.
One final note: Giardia does pose a potential health risk to humans. Standard hygiene practices reduce this risk dramatically. Dogs that shed Giardia organisms pose the greatest (although still highly debatable) threat. Talk to your vet about this.
Photo: The background is brown because it's poop. By Kalumet.