Giardia: Causes

General Symptoms:

Since canine giardia affects the digestive system of the dog, symptoms are particularly limited to the small or large intestine. The overall disturbance in body the body is thereby related to the physiology of digestive system.

dog giardia
Dog Giardia is caused by the protozoa pictured here
Source: testinalis trophozoites in Kohn stain. Center: G. intestinalis  cyst stained with trichrome. Right: G. intestinalis in in vitro culture, from a quality control slide. Credit: DPDx

The Main Causes:

Giardia is ingested in the form of cysts, which are freely excreted in the environment by affected dogs. An active form of protozoa, called Trophozoites is released in the small or large intestine, which attachers to the thin lining of the intestine. They not only absorb nutrients but also cover the intestinal lining, thus preventing absorption of nutrients through the intestinal wall.

Therefore, a dog with a heavy infestation of giardia is left with diarrhea, occasional vomiting and weight loss in the span of a few days. It should be remembered that these symptoms are only exhibited in true giardia disease; a mild infection may never cause any symptoms at all.

Specific Giardia Symptoms:

Major symptoms related with the giardia infection in dogs is diarrhea. Particularly, this form of diarrhea is also called steatorrhea, which means that it contains excess fats. The thin lining of intestine is badly damaged by infection; therefore diarrhea contains mucus and fats. Diarrhea may be acute, intermittent or chronic in nature and occurs in small quantities; specifically called small-bowel diarrhea.

In mild to severe giardial infections, feces appear to be deformed, have a bad odor, are pale, contain mucus and appear fatty. Watery diarrhea is not noticed in uncomplicated cases of dog giardia. Giardia symptoms in puppies are more prone to severe cases of the symptoms described for adults. The intestinal lining is damaged badly, but blood is never passed in the feces. Nutrients are not properly absorbed through the intestine, therefore an affected dog may lose weight over time, but loss of appetite is unusual. The overall physiology of the body may be affected and acute weakness is felt during true disease.

Clinically, a dog with a mild chronic giardia infection appears to be normal, except for soft, odorous and pale feces. In such cases, clinical laboratory procedures are reported as normal. Microscopic lesions over the intestine with atrophy on villi are noticed. Additionally, laboratory studies at the clinic can reveal severe malabsorption of nutrients, reduced intestinal carbohydrates and heavy infiltration of lymphocytes in the digestive tract; which represents giardial or any possible protozoal infestation.


Clinical symptoms of acute, intermittent or chronic diarrhea with excessive fats in it should be suspected for giardia, but confirmation can only be made through repeated use of the fecal flotation technique, in which giardia cysts can be observed in a saline smear of the diarrhea/feces. Giardia Cysts are usually not released with every excretion; therefore repeated testing 3x a day for at least 3 – 5 days is required for confirmation.

Detection of the specific giardia antigen in the fecal sample is another technique sued for confirmation, but that does not help in detecting the form or severity of disease.

Dog giardia should be differentiated from other causes of nutrient malabsorption; like those caused by exocrine pancreatic insufficiency, malabsorption syndromes and any other protozal or bacterial infection.


Unfortunately, there is no approved treatment for giardia in dogs. There needs to be more research about the life cycle and mode of infection of this disease. Several anti-parasitic drugs such can effectively treat canine giardia symptoms without prominent side effects including:

Additional measures, such as the administration of supportive remedies which enhance the physiology or condition of the digestive system and absorption of nutrients such as the remedy Digestive Support can be helpful. Others, such as Parasite Dr. can  help to reduce protozoal infestation.  Firm stool formation can be promoted with a natural product like Natural Moves. Each can effectively treat the giardia symptoms. These remedies are for support only and should be administered along with specific anti-parasitic drugs prescribed by a veterinarian.