Giardia: What is it?
Every pet has experienced diarrhea at some point in its lifetime. There are many causes of diarrhea. Dietary indiscretion, eating the wrong thing, is often the culprit, but diarrhea can be a symptom of a more serious problem. This includes disorders such as gastroenteritis, inflammatory bowel disease, or cancer. Each of these topics warrants an article all to itself at another time. This article, however, will focus on another main cause of diarrhea, parasites, and one little bugger, in particular, Giardia.
Giardia, or more formally called Giardia duodenalis, is not what we normally imagine a parasite to be. It is not a worm but a simple one-celled organism or protozoa. Giardia parasites move around using their long tentacles, called flagella, which further classifies them as flagellates. They use this flagella to move about in the host’s intestines, ultimately finding a spot and attaching there with a suction cup-like structure. Once attached, their presence in the intestine can lead to diarrhea.
Infection from Giardia, called giardiasis, occurs worldwide in animals and people. Currently, eight “strains” of this parasite are recognized and certain strains are associated with dogs, cats, and people. Pets can transmit Giardia to their unsuspecting owners, but fortunately, transmission from pet to human is rare.
Giardia exists in two forms, a motile form called a trophozoite, and a cyst form. The cyst acts as a shell to protect the fragile trophozoite that is housed within it. The cystic form of Giardia can persist for several months
Transmission of Giardia occurs when the cyst is ingested, and then passes to the intestines. Once in the intestine, the trophozoites or feeding form of the parasite is freed from the shelllike cyst, matures, and multiplies in the intestines. The presence of the trophozoite in sufficient numbers can lead to clinical giardiasis where the intestines do not perform normally and damage to the intestinal wall can occur with subsequent diarrhea. Additional symptoms can include fever, dehydration, vomiting, and abdominal pain.
Once infected, new cysts containing the trophozoites are formed in the infected animal and then passed in the stool, where they can then infect a new host. The time it takes from ingestion of cysts to passing it in the feces is approximately 5-15 days in a cat and 5-12 days in a dog. In many pets, eating the infectious cysts do not cause any symptoms, or at most a mild transient soft stool. In puppies, kittens, or older, compromised pets, clinical Giardia can be very serious and life-threatening.
Giardia is sometimes discovered via a routine fecal flotation test, but they can be tricky to diagnose as the cysts are shed intermittently. Specific tests are often used to detect giardia including a test called a Giardia PCR that looks for cell proteins specifically associated with giardia. Once the diagnosis is confirmed, Giardia is treated with one of two medications, fenbendazole or metronidazole. These medications are generally very effective in eliminating giardia, but sometimes need to be given in combination. Once completed your veterinarian will suggest a recheck fecal test in 2-4 weeks to be sure no further treatment is indicated. Prognosis is generally good for most pets. Because Giardia can be rarely passed between pets and humans, it is important to practice good hygiene, disinfect, and remove infected stool from the environment to prevent additional exposure. Bathing also helps to keep cysts off the hair coat.
There are many opportunities for our pets to encounter Giardia, eating grass, drinking from a puddle or a stream on a hike, or eating poop, all of which can introduce infective cysts. Avoiding those places with lots of fecal material present, or expected, and always having clean and safe water for your pets to drink will go a long way in preventing giardiasis.