What is it?

Giarda is a microscopic parasite, a protozoan, that lives in animals' intestines.

It is the most common protozoan in North America. Thirty to thirty five percent of puppies less than six months of age are carriers of the parasite. 

The symptoms

The animal infected with this parasite produces pale, diarrheal stools with mucus intermittently.

The parasite life cycle

Dogs often become infected when they ingest cysts containing the infectious form of the parasite, a trophozoite, in the environment. 

Digestion of each of the cysts in the duodenum (first portion of the small intestine) will release two trophozoites that will cling to the intestinal cells where they will reproduce.

Subsequently, the parasites will encyst and lodge themselves in the wall of the colon until they are excreted intermittently in the dog's feces, where in which they will already be infectious. 

The life cycle spans between 6 and 8 days in dogs. It begins the moment where the animal infects itself with cysts present in the environment and ends when new cysts are expulsed in the feces.

The transmission

The infection is acquired by ingesting contaminated feces or water. 

Is the parasite contagious to humans?

The answer is yes! 

However, when people contract Giarda, they often catch it from another person more often than dogs.

Furthermore, individuals who are immunosuppressed, meaning that they have a weakened immune system, are more susceptible to contracting the parasite. 

The diagnosis

Because the parasite is not visible to the naked eye, other methods must be used to confirm its presence. 

For example, a smear can be done directly. This test consists of mixing a drop of freshly collected feces with a drop of saline and to view it under a microscope. It is sometimes possible to see the protozoan moving; its movement resembles a leaf falling from a tree or it can be seen turning around itself. 

Another test that can be performed is the "Snap Test", an enzyme immunoassay that allows rapid detection of parasite antigens. 

Finally, another test that exists is the PCR (Polymerase Chain Reaction). This tests detects the presence of the Giarda's DNA in the patient's feces. 

The treatment

Prescription medications that are safe and effective are available to treat this parasitosis. 


It is important to retrieve the cats' feces as quickly as possible after their excretion. 

As a precaution, it is always best to wear gloves when handling stools and, above all, wash your hands properly afterwards. Furthermore, vegetables from the garden should be well cleaned before being eaten.

Due to the high degree of contagion of this parasite, infected cats should also be isolated.