Life Cycle of Giardia in Dogs


Giardiasis in dogs is actually intestinal infection and infestation of a protozoan genus known as Giardia. There are many species of Giardia but Giardia duodenalis is found in dogs and cats – (Reference). This disease is also common in humans and other animals. Some other common names of this disease are “Traveler’s Diarrhoea”  & “Beaver’s Fever“. 

Giardia is neither a Bacteria nor a virus, it’s a protozoan.

Some other example of protozoans are Coccidia, Cryptosporidia & Toxoplasma. They all cause different kind of diseases e.g. coccidiosis.


Life Cycle of Giardia in Dogs:

Life Cycle of Giardia in Dogs

Giardia, just like other protozoans, has two form or living stages, Cyst form & Feeding/Trophozoite form.  Cyst is the dormant and resistive form and cysts are shed into the environment with the faeces. The other feeding or Trophozoite form is the active, feeding and reproductive form. This form is adopted inside the intestine of infected animal.

The life cycle start with the entrance of cystic form inside the animal, this cystic form converts itself to feeding form, Trophozoites. Trophozoite eat and replicate via binary fission. After 3-10 days encysted trophozoite and cysts start coming out with the faeces of the animals. These cysts when get entry, via ingestion of food or water intake, multiply and next life cycle starts.

Clinical Signs:

Dogs suffering from the giardiasis show signs of diarrhoea. The faeces become foul smelling and it become watery to soft. Large amount of “Mucin” comes in the faeces. Due to intestinal damage, dogs also show signs of dehydrations and anorexia. There may be vomiting. Some dogs don’t show any kind of signs after infection but they also shed cysts in their faeces intermittently.  Blood is usually NOT present in stool of “giardia” infected animals.

Diagnosis of Giardia:

The most common indication of Giardiasis is diarrhoea and it can be easily diagnosed after enquiring the disease history. Diagnosis can also be defended with floatation and centrifugation techniques. Sometimes flagellate trophozoites can be seen by making the smear of fresh faecal sample.

The oval cysts (9–15 × 7–10 μm) can be detected in feces concentrated by the centrifugation-flotation technique using zinc sulfate (specific gravity 1.18).  

Giardia cysts are shed intermittently so many samples are taken for 2-3 days. Staining with iodine can also help identifying the giardia cyst.

Giardia in Faecal Sample
Courtesy of Dr. Roger Klingenberg

For identification of parasite antigen immunofluorescence assays and ELISA tests are also commercially available and these tests are considered best for confirmation of diagnosis.


Treatment depend on the condition of the patient. Sometime dogs recover after short period of illness. The main objective of the treatment is to remove the parasitic protozoa. Most commonly used drug for this disease is “Metronedazole“. Metronedazole is given for 5-7 days and repeat faecal sample checking should be performed to check the presence or absence of cysts.

Metronedazole is not a safe drug to pregnant animals.

Fenbendazole is also a good choice and it should be prescribed for 7-10 days. It don’t have any side-affects. A safe strategy is to use fenbendazole first in dogs and cats, because metronedazole is not considered good for dogs and cats.



Control of Giardiasis:

As the most common route of infection is the ingestion of cysts, so such crowded environment should be avoided in kennel and catteries. Best control is to remove the cysts from the surroundings and environment. A disinfectant, bleach or lysol, can be used to wash the area. To increase the efficacy of disinfectants, solutions should be left for 5–20 min before being rinsed off contaminated surfaces. Cysts can also be  inactivated by most quaternary ammonium compounds, steam, and boiling water. Dry and hot conditions also eliminate cysts.

Infected dog should be separated from the healthy pets. A good body wash is also good for infected dogs. Fast washing and removal of faeces is considered important. Prevention of re-introduction of giardia is very important.

Dogs owners and handler should also wear gloves while handling the infected dog.

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Jawad Ahmad is veterinary graduate from Asia's best veterinary university, University Of Veterinary And Animal Sciences, Lahore, Pakistan. He loves to blog and work as a freelance writer for biosciences niche. He joined "Veterinary Hub" in June 2013 as an author. He is currently a post-graduate student in Department of Pathology, University of Veterinary & Animal Sciences, Lahore.