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Giardia in Dogs

Giardia is a cosmopolitan parasite that has spread throughout the world. It affects both humans and animals. This flagellated parasite is host-adapted, meaning that every animal, including dogs, is affected with its own specific strain. Giardia loves to reside in cold and wet environments, so every source of water outside bears a risk of a possible infection with this parasite. The route of transmission is fecal-oral. It resides in the small intestine and has a great impact on the digestion and the whole gastrointestinal tract.

In most cases, it causes foul-smelling diarrhea and vomiting, which impairs the general well-being and quality of the dog’s life. Giardiasis is a treatable disease that is not life-threatening if it is treated in time. Therefore it is important to take preventive measures and pay attention to any signs or symptoms in the dog. This will surely prevent further complications and lower the possibility of the disease becoming chronic. In this article you can find out more details about the ways of transmission, symptoms, treatment, and the preventive measures you can take to minimize the risk of this parasite.

What Is Giardia in Dogs and What Does It Do?

Giardia is a single-celled parasite. Unlike other well-known “worms,” it is only seen under a microscope. It has a flagellum, which is used for movement. This flagellum helps it to get to the small intestine where it attaches to the mucosal surface. This is where it absorbs nutrients and reproduces. Giardias are called trophozoites in this stage, but after 3-10 days, they encyst.1Yaeger RG. Protozoa: Structure, Classification, Growth, and Development. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 77.

As a cyst, Giardia becomes infectious, and through feces, it sheds into the environment, thus increasing the risk of disease for other dogs, animals, and humans.

In the intestines, Giardia prevents proper absorption of nutrients, water, and electrolytes from food and decreases the activity of the microvilli and the enzymes they produce. This all leads to diarrhea, malnourishment, and weight loss.

Cold, high humidity and wet places are Giardia’s favorite environment. Once inside a host, they can continue with their reproduction.

Giardia Symptoms in Dogs

Considering the pathway Giardia takes to induce infection—by getting attached to the mucosal surface of the small intestines—the major clinical signs the dog develops are related to the digestive tract. This is why one of the most peculiar symptoms is the sudden occurrence of profuse, foul-smelling diarrhea.

The feces’ consistency can be watery or rather soft, oftentimes with a greenish color and sometimes, in more severe cases, blood can be found in the feces. As a result of improper food digestion, a mucus layer and a fatty stool (steatorrhea) occur as well. If the diarrhea persists, it can cause noticeable weight loss. The diarrhea can also become rather chronic and intermittent.

Other clinical symptoms may include the following:

  • Vomiting
  • Gas (flatulence)
  • Lack of appetite
  • Apathy

Clinical signs can range from asymptomatic (no symtpoms) to severe cases, thus the disease can either have an acute, chronic or intermittent timeframe. In cases where dogs do not show any clinical signs, they can be just carriers of the disease, making it more difficult to control the spreading of the disease.

Giardiasis itself is not a life-threatening disease, especially if treated on time. Yet, more caution should be given to immunocompromised dogs and younger dogs, such as puppies whose immune system is still not mature and strong enough to fight the disease.

Giardia in Puppies

Puppies are amongst those whose immune system is still immature and not fully developed, thus the Giardia parasite can cause greater damage. They are more likely to show more apparent clinical signs than adult dogs. Profuse diarrhea, either soft and lightly tinted, or stool with blood and mucus mixed together, is the most prominent sign of Giardia in puppies.

The puppy infected with Giardia refuses to eat, and his energy levels drop; you will notice that he is not as playful or as cheerful. His belly will be bloated and full of gas as a result of indigestion.

In this stage of a dog’s life, good healthy nutrition is crucial for proper development and growth. This could be compromised by Giardia since the ability to digest food properly will be decreased. Consequently, he will have trouble gaining and maintaining weight in a healthy range.

So, if you notice any of these signs or think there is a possibility your puppy came in contact with Giardia, make an appointment at your vet as soon as possible so further damage can be prevented and your puppy stays healthy and in good shape.

How Do Dogs Get Giardia?

The route of transmission is fecal-oral because, like mentioned before, the infectious cysts are discharged within the dogs’ feces. Therefore, a dog can get infected by ingesting the infectious stool of another dog. This can occur in various ways, including direct contact with the other infected dogs or by ingesting fecally contaminated water, food or objects.

Giardia cysts are rather resistant, so if not controlled, the risk of Giardia infection can get progressively greater. The dog ingests the cyst through fecally contaminated food or water. Contaminated water is one of the most common ways dogs get infected with this parasite since it prefers great humidity for its persistence.

Kennels, dog shelters, or any other crowded place with a greater number of dogs is an excellent place for Giardia to multiply and transmit successfully.

Giardia Diagnosis in Dogs

If the veterinarian assumes that the dog has been infected with the Giardia parasite, after examining the current state of the dog and taking into consideration the clinical signs, he will take stool samples. There are various tests that can be conducted, including fecal smears, flotation method, immunofluorescence assay, and ELISA test; the last two detect the parasites’ specific antigens found in the feces. The test costs around $20-$50.

Treatment for Giardia in Dogs

After the diagnosis has been established, the veterinarian will suggest treatment according to the dog’s current condition and stage of disease. Since there is no approved, specific drug that gets rid of Giardia, veterinarians usually tend to use broad-spectrum antiparasitic drugs such as Fenbendazole.

Fenbendazole is generally used for various gastrointestinal parasitic worms (roundworms, hookworms, tapeworms, whipworms, etc.). However, it has also been found to be a very powerful tool against Giardia cysts, efficiently removing them from the dog’s feces. There were no reported major side effects as well, making it a safe remedy even for lactating and pregnant dogs.

One of the other options the veterinarian might suggest is Metronidazole, but its effectiveness lays at 67%, and there are some implications of resistance of Giardia to this drug.2Anderson, K. A., Brooks, A. S., Morrison, A. L., Reid-Smith, R. J., Martin, S. W., Benn, D. M., & Peregrine, A. S. (2004). Impact of Giardia vaccination on asymptomatic Giardia infections in dogs at a research facility. The Canadian veterinary journal = La revue veterinaire canadienne, 45(11), 924–930.

A combination of pyrantel, praziquantel, and febantel is likewise one of the possible methods of treatment.

Nitazoxanide, a drug usually used for human Giardiasis, has shown its efficacy in dogs recently as well, but it has not yet gotten its place in everyday practice.3Moron-Soto, Mario & Gutierrez, Lilia & Sumano, Hector & Tapia, Graciela & Alcala-Canto, Yazmin. (2017). Efficacy of nitazoxanide to treat natural Giardia infections in dogs. Parasites & Vectors. 10. 10.1186/s13071-017-1998-7.

If the condition is neglected, the dog can become dehydrated and malnutritioned. Consequently, the general health status gets corrupted and disturbed since there is no proper absorption of nutrients that are essential for a normal functioning organism. Also, there is a great possibility of shedding the infectious cysts, thus contaminating the environment and increasing the risk to public health.

Therefore, part of the treatment is also supportive therapy (vitamins, minerals, probiotics), which will repair the side damage Giardia made and also prevent further problems. Good hygiene and keeping the dog and the environment clean is important to prevent reinfections.

It is recommended for the Giardia test to be repeated, usually two to four weeks post-treatment, to lower the risk of contamination and to ensure the safety of your environment.

How to Prevent Giardia in Dogs?

Giardia loves to reside in cold and high-humidity environments, thus any type of water sources, like ponds, lakes, fountains, riverbanks, and streams, can be a source of infection. Therefore, it is highly recommended that the dog always has plenty of fresh, clean drinking water available. When going out, especially for a longer period of time, try to carry a portable bottle and/or a bowl with you.

This is how you can limit the chance of the dog drinking dirty outside water. Yet, attention should be kept at all times, so if you see the dog drinking, stop him as soon as possible.

Great attention should also be given when in contact with other dogs, especially when there are water sources nearby.

Can Giardia Be Passed From Dog to Human?

Giardiasis is indeed a pretty common disease in both dogs and humans, yet the possibility for humans to get Giardia from their dog is pretty low. From six known Giardia species, only one is able to infect humans and other mammals: Giardia duodenalis.

Giardia duodenalis has different assemblages from A-H, classified upon their genetic variability and host specificity. The A and B assemblage are found in humans, whereas the C and D infect dogs and other canids. This is why it was found that only 2% of infected dogs can potentially have a strain of Giardia that can be transmitted to their owners.4Inpankaew, T., Schär, F., Odermatt, P., Dalsgaard, A., Chimnoi, W., Khieu, V., Muth, S., & Traub, R. J. (2014). Low risk for transmission of zoonotic Giardia duodenalis from dogs to humans in rural Cambodia. Parasites & vectors, 7, 412.

Despite the low possibility, you should take measures of precaution. The first step is regularly washing your hands primarily after playing with your dog or touching anything that your dog came in contact with from their food, toys, and places they sleep. Particular attention should be given after handling and cleaning their poop. The surfaces where they reside should be kept clean and disinfected as frequently as possible.


Giardia is a widely spread and very common parasite amongst dogs, other animals, and humans. By attaching to the small intestine, it can cause profuse, foul-smelling diarrhea. Even though it is not a life-threatening disease, it can cause malnourishment and severe weight loss, which can result in a chronic condition. For this reason, it should not be neglected.

There are several fecal examinations that can be done for a final diagnosis, after which proper treatment is suggested. In most cases, antiparasitic Fenbendazol together with supportive therapy is recommended.

The fact that Giardiasis can also go unnoticed in some cases indicates the importance of greater preventive measures that should be taken to minimize the transmission of these protozoan cysts. For more information on Giardia prevention please read the “How to Prevent Giardia in Dogs” section.

If you see any symptoms or suspect anything that could indicate your dog has been infected with Giardia, contact your vet for further instructions.

Frequently Asked Question (FAQs) About Giardia in Dogs

How to Treat Giardia in Dogs?

In most cases, Giardia is treated with Fenbendazole, a broad-spectrum antiparasitic, which has shown to be very effective against Giardia, with no detected side effects. Other drugs like metronidazole and a combination of pyrantel, praziquantel, febantel and lately nitazoxanide can also be used. To learn more about Giardia treatment, read the section “Treatment for Giardia in Dogs.”

Can Giardia Cause Long-Term Problems in Dogs?

If the treatment is postponed and not done correctly, long-term consequences can be developed. The parasite damages the dog’s digestive system, which leads to malabsorption and then malnutrition; consequently, the general health condition becomes compromised.

How to Naturally Cure Giardia in a Dog?

There is no natural treatment that has been standardized nor proven to be effective yet. For any further questions and instructions, contact your veterinarian.

How Long Does Giardia Last in Dogs?

If the treatment was successfully carried out, the dog can be expected to be free of Giardia after two weeks. In some, more severe cases, it can be somewhat prolonged. Retesting should be done two to four weeks post-treatment. Great attention should also be given to cleaning up the environment as well as thoroughly bathing the dog to make sure there are no Giardia cysts present.

Should Dogs With Giardia Be Quarantined?

Dogs with Giardia should be quarantined in case they live together with other dogs, animals, or in breeding facilities. They should have a separate place for defecating and urinating. In this way, further spread of the Giardia cysts can be prevented.

Dr. Iman Krijestorac (DVM)
Dr. Iman is a young, ambitious veterinarian working in a small animal vet station while volunteering in the local dog shelter. Zoonotic and infectious diseases are one of her major interests, together with dog nutrition and diet for which she attended several seminars and conferences. She has always had a heart for big dogs, she has an old Appenzeller Sennenhund going by the name "Yoda".

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