What is Giardia?

Giardiasis refers to an intestinal infection that is caused by the protozoan parasite giardia. Dogs develop the infection by ingesting infectious offspring (cysts) that are shed in another animal's feces. The contamination can be from direct or indirect contact with the infected cysts. The organisms, once ingested, make their way into the intestine, often causing diarrhea. The treatment is typically performed on an outpatient basis with an ex excellent prognosis.

The Microscopic parasite clings to the surface of the intestine, or floats free in the mucous lining the intestine. Veterinary research documents suggest that 5% to 10% of all dogs in North America have giardiasis at any given time.

Surveys also show that about 14% of the adult dog population and over 30% of dogs under one year of age were infected at some point during their life, and thus contributed to passing along this intestinal infection to other dogs. Another Vet research article I found suggests that 100% of kennel dogs, 50% of pups, and 10% of well-cared for dogs carry giardia.

Life Cycle of Giardia
in two forms: a motile feeding stage that lives in the intestine, and a non-motile cyst stage that passes in the feces. The giardia trophozoite - which is the active stage of the organism - inhabits the small intestine of the dog. The trophozoite stage is tear-drop shaped, binucleated, and has four pairs of flagella. It attaches to the cells of the intestine with its adhesive disc and rapidly divides to produce a whole population of trophozoites. As they detach they may be swept down the intestine. If intestinal flow is fast then they may appear in the feces. However, if they have time, encystment occurs as the parasite travels to the large intestine. The cyst is fairly resistant, and can survive for several months outside of a host's body as long as sufficient moisture is provided. The cyst is oblong in shape with four nuclei that are sometimes distinctly visible. Mature cysts are usually found in the feces of infected animals. Other animals become infected by ingesting the cysts that passed from the body in feces. These ingested cysts then break open inside the small intestine to release the motile feeding stage (trophozoite). Giardia increase their numbers by each organism dividing in half which is called binary fission

The trophozoites divide to produce a large population, then they begin to interfere with the absorption of food. Clinical signs range from none in asymptomatic carriers, to mild recurring diarrhea consisting of soft, light-colored stools, to acute explosive diarrhea in severe cases. Other signs associated with giardiasis are weight loss, listlessness, fatigue, mucus in the stool, and anorexia. These signs are also associated with other diseases of the intestinal tract, and are not specific to giardiasis. These signs, together with the beginning of cyst shedding, begin about one week post-infection. There may be additional signs of large intestinal irritation, such as straining and even small amounts of blood in the feces. Usually the blood picture of affected animals is normal, though occasionally there is a slight increase in the number of white blood cells and mild anemia. Without treatment, the condition may continue, either chronically or intermittently, for weeks or months.

Giardia lives and reproduces in the small intestine of host animals. Giardia trophozoites, the free living stage of the organism, form infective cysts that are passed out in the feces. If the cysts are present in a wet or damp environment they can survive in a viable state for a few weeks to several months. Giardia infections are transmitted via ingestion of trophozoites or cysts in contaminated water or food. If a giardia cyst is ingested, the cyst wall is broken down during the digestive process and the trophozoite stage begins to colonize the upper small intestine. Transmission also occurs by direct contact, especially with asymptomatic carriers. More recently, giardiasis has also been recognized as being able to be sexually transmitted. Giardia is so prevalent throughout North America because it is highly contagious. The ingestion of as few as one or more giardia cysts may cause the disease, as contrasted to most bacterial illnesses where hundreds to thousands of organisms must be consumed to produce illness. Up to 50 percent of young puppies will develop this intestinal infection, and up to 100 percent of dogs housed in kennels will develop it due to the massive exposure and closely shared living spaces.

Diagnosis can be done in one of two ways: via fecal sample by a Vet or via educated evaluation of clinical findings by the breeder/owner or the Vet. Via fecal sample is not straightforward. Even when a flare is at it's worst, the cysts will not be shedding in every single stool. Therefore, a negative report does not rule out giardia. The most thorough way to assess is to collect a sample from every single stool produced for 48 to 72 hours and have a Vet examine it using the giardia test kit.

The giardia test is a monoclonal antibody-based ELISA for the rapid detection of Giardia lamblia cysts antigen in stool specimens and serves as an in vitro aid in the diagnosis of giardiasis..

Infection may be treated using one of a number of different drugs that are available through a Vet Supply Store. The treatment of choice is with Metronidazole 250mg. Metronidazole has two interesting properties - the action is largely confined to the gut and it also seems to stimulate the local immune system. Metronidazole kills off the giardia and reduces the numbers to the level the dog's immune system can handle. Alternatively, you may want to use Fenbendazole (Safe-Guard or Panacur). Fenbendazole is a very safe medication as a treatment for deworming your dogs. This is my second choice for kennel use. The same dosage and three-day deworming treatment using Fenbendazole for deworming dogs will also rid your dogs of the giardia protozoan.

Treatments from the Vet research literature that I found are shown in the table below. Whatever treatment is chosen, it is very unlikely to eliminate 100% of the infection in all dogs. Adaptations that may be made to try to improve the success rate of a treatment regime include extending the duration and dose of the treatment. Care must obviously be taken with this approach to make sure that an adequate safety margin is always maintained. Another approach is to retreat after an interval of one week. Alternatively, repeat fecal samples may be collected one week after the treatment and dogs which are still passing cysts can be identified and treated. It should be recognized that, when treating a large number of dogs, whichever of these treatment strategies is adopted, there may be one or two dogs that remain as carriers of infection that will act as a potential source for reintroducing the infection into your entire kennel.

Treatments for giardiasis in dogs.
This information is taken straight out of the Vet Medical Manual.


Drug Name Trade Name Dose Rate Duration of
Metronidazole Flagyl 11.5 to 15 mg/lb BID** 5 days
Furazolidone Neftin 2 mg/lb BID* 10 days
Tinadazole - 22 mg/lb once daily 7 days
Fenbendazole Safe-Guard or Panacur*** 22.5 to 25 mg/lb once daily 3 days
Albendazole Valbazen 12 mg/lb BID 2 days
Bid = Twice Daily
* Maximum daily dose 200 mg.
** Contraindicated in pregnancy
*** Licensed for the treatment of worm infections in dogs

I recommend that you also see the page on Coccidiosis to learn more about the other common protozoal infection called coccidiosis. No matter which treatment you choose to utilize, the simple fact is that it may not kill all of the cysts. A certain number of them can burrow into the lining of the intestines and go dormant. They can stay dormant for years. Due to the hard shell protecting the cysts, it is almost impossible to kill them when they are encysted in the lining of the intestines. Therefore, during times of stress, the cysts may re-activate and start to reproduce, causing another outbreak of giardiasis in your dog or kennel. The amount of stress needed to cause a flare seems to be highly variable with different dogs and dog breeds.

Since one of the highest incidences of the infection spreading is in a kennel, boarding kennel and dog parks seek places that offer private spaces for pets in order to avoid contamination from the other animals

We hope these tips help you and your new puppy enjoy a long healthy life!!