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Navigating Giardia in Dogs: From Understanding to Nourishing

The dance of Giardia in your dog’s digestive system is a saga of persistence and resilience. In this article, I will delve deep into the world of this single-celled parasite to understand its modus operandi and how to tackle it effectively. From its love for lipids to its intricate life cycle, and from the symptomatic waxing and waning to the role of diet in managing an infection, we’ll unveil the mysterious dance of Giardia.

The Intruder Unmasked: Unraveling Giardia in Dogs

In the mysterious world of microscopic parasites, Giardia holds a notorious reputation. But what exactly is this tiny bugger? Giardia is a microscopic parasite that can infest your dog’s gut, leading to a condition known as giardiasis. Derived from its discoverer, Alfred Mathieu Giard, the term “giardia” refers to these elusive, single-celled organisms that wreak havoc on your dog’s digestive system.

Demystifying Giardia

Giardia, the unwanted guest in your dog’s gut, is incredibly small but causes large-scale chaos. These parasites latch onto the intestines, feeding on your dog’s nutrients and interfering with proper digestion. The primary signs of this unwanted visitor are diarrhea, vomiting, weight loss, and generally a poor condition.

A Peek into the Parasite’s Life Cycle

Giardia has a unique lifecycle that begins as a dormant cyst excreted in an infected animal’s feces. These cysts are quite resistant and can survive in various environments – from water bodies to contaminated surfaces.

Upon entering your dog’s digestive tract, the acidic environment in the stomach triggers the cysts to awaken. The cysts metamorphose into the active form of the parasite, known as trophozoites. These trophozoites have a unique, teardrop-shaped appearance with whip-like appendages called flagella that aid in their movement.

Trophozoites thrive in the small intestine, reproducing and ultimately transforming back into cysts, which are then passed in the dog’s feces, ready to start the cycle anew.

Colonization and Replication: Establishing the Parasitic Colony

The trophozoites journey down to the small intestine, where they attach themselves to the intestinal wall, specifically the microvilli. These are the nutrient factories of Giardia – they feed on the readily available nutrients here, absorbing them directly through their cell membrane.

As Giardia parasites multiply, they cause damage to the microvilli, reducing the surface area available for nutrient absorption and leading to malabsorption issues for your dog.

The Cyclical Nature of Giardia Symptoms

Understanding the life cycle of Giardia can help demystify why the symptoms of infection can seem to wax and wane. Let’s explore this mysterious dance between the parasite and its canine host.

The Stages of Giardia: Trophozoites and Cysts

If you recall, giardia exists in two main forms: trophozoites, which are the active, disease-causing form, and cysts, which are the dormant, resistant form.

Trophozoites are the ones causing the mischief in your dog’s intestines. They attach to the intestinal lining and feed, multiply, and cause the troubling symptoms associated with Giardia infection. After a while, these trophozoites morph into cysts, which are then passed into the dog’s feces.

Cyst-Protozoan Dance: The Wax and Wane

The symptoms of Giardia infection wax and wane due to this cycle of transformation between the trophozoite and cyst forms. When the trophozoites are actively causing inflammation and interfering with digestion in the intestines, your dog may exhibit more severe symptoms like diarrhea, vomiting, and reduced appetite.

As the trophozoites transition into cysts and are excreted, the active disease-causing population in the gut diminishes, leading to a temporary abatement or lessening of symptoms. This is the ‘waning’ phase.

However, some of the cysts excreted in the feces can contaminate the environment and be ingested again (either by the same dog or other dogs). Once ingested, these cysts transform back into trophozoites in the gut and restart the disease-causing process. This could lead to a ‘waxing’ of symptoms, marking a resurgence of the infection.

And even though the video below is on Giardia in humans, I’m sharing it because it can shed more light on this parasite.

The Protective Ploy: Immune Response

Also, the dog’s immune system plays a role in this cycle. As the immune system fights off the infection, symptoms may wane. However, if the dog’s immune response isn’t strong enough to eliminate the infection entirely, or if reinfection occurs, the symptoms may wax again.

In essence, the cycle of Giardia and the body’s immune response creates a rhythm of waxing and waning symptoms, making Giardia a challenging and often persistent opponent. This underlines the importance of effective treatment and good hygiene practices to break the cycle and prevent reinfection.

Giardia’s Favorite Dish

Giardia parasites feast on your dog’s nutrients, which they absorb through their cell membranes. This parasitic feast disrupts your dog’s ability to absorb crucial nutrients from the food they eat, leading to symptoms like diarrhea and weight loss.

Giardia’s parasitic journey within your dog’s gut centers on a nutrient heist. But what precisely does Giardia feed on?

Feeding on the Premises: The Microvilli Buffet

Your dog’s small intestine is lined with tiny, finger-like projections known as microvilli. These structures increase the surface area of the intestine, making nutrient absorption more efficient. And for Giardia, this setup is akin to a vast buffet. These parasites can absorb nutrients directly through their cell membranes in a process known as pinocytosis.

Giardia parasites attach themselves to the microvilli, sapping up the nutrients the host’s body has already broken down for absorption. In essence, they’re stealing food right off your dog’s plate.

Giardia is not your typical parasite – it thrives under specific conditions that other organisms might find inhospitable. Low oxygen levels, high cysteine concentration, and the need for exogenous lipids – let’s break down why Giardia can’t get enough of these.

Low Oxygen: The Anaerobic Nature of Giardia

Giardia is an anaerobic organism, which means it doesn’t need oxygen to grow and survive. In fact, high oxygen levels can be harmful to it. This makes the small intestine a perfect home for Giardia. The oxygen levels in the intestine are lower than in other parts of the body due to its role in digestion, which requires an anaerobic environment.

The Love for Cysteine

Giardia has a high demand for cysteine, a sulfur-containing amino acid. Cysteine acts as an antioxidant, neutralizing harmful substances that could potentially damage the parasite. The anaerobic environment in which Giardia thrives can promote the production of harmful substances, making cysteine crucial for Giardia’s survival.

Additionally, cysteine serves as a building block for the parasite’s protein synthesis and plays a role in its cyst wall formation. The cyst form is the one that’s resistant to outside conditions and can survive outside the host, ensuring the continuation of the Giardia lifecycle.

The Need for Exogenous Lipids

Unlike many other organisms, Giardia cannot synthesize its own lipids – fats and fat-like substances – that are essential for building its cell membranes and other vital functions. Hence, it relies on “exogenous” lipids, meaning it must obtain these from its environment, in this case, the host’s gut contents.

These lipids are absorbed through the cell membrane of Giardia and are used for various functions, including energy storage, cell signaling, and as structural components of its cellular membranes. In a sense, the parasite is living off the fat of the land – or in this case, the fat of the dog.

Glucose for Energy

Glucose: As for glucose, it’s the primary source of energy for Giardia. It absorbs glucose from its surrounding environment in the intestines and metabolizes it through anaerobic (oxygen-less) processes to obtain the energy it needs for survival and reproduction.

The Perfect Environment for a Pesky Parasite

These requirements mean that Giardia has carved out a niche for itself in the low-oxygen, nutrient-rich environment of your dog’s small intestine. Understanding these conditions can help us better understand the nature of this parasite and how to fight it.

When the Feast Becomes a Famine: Giardia’s Impact on Your Dog

Giardia’s feeding frenzy has serious implications for your dog’s health. By robbing your dog’s gut of vital nutrients, Giardia can cause malnutrition, weight loss, and general debilitation. Furthermore, their presence and the inflammatory response they trigger can damage the intestinal lining, leading to symptoms like diarrhea and poor digestion.

Fighting the Fiend: Giardia Treatments

Treating Giardia involves a tag team of two medications, typically Fenbendazole and Metronidazole. These drugs help eliminate the active trophozoites, allowing your dog’s gut to start healing.

Metronidazole: The Anti-Giardia Gladiator

Coming to the rescue is Metronidazole, an antimicrobial medication that’s often the go-to for treating Giardia infections in dogs. This drug doesn’t merely control the symptoms – it fights Giardia trophozoites directly.

Metronidazole works by penetrating the cell structure of the trophozoites and interfering with their DNA and proteins. It prevents the trophozoites from multiplying, halting the infection in its tracks. However, it doesn’t impact the cysts – so sanitation is key to preventing reinfection.

Administering Metronidazole

Metronidazole is typically given orally and can be administered with food to help reduce potential side effects, such as nausea. As with any medication, it’s essential to follow your vet’s instructions regarding dosage and duration of treatment.

Possible Side Effects

While metronidazole is generally safe for most dogs, some may experience side effects like loss of appetite, nausea, vomiting, or diarrhea. More severe but rare side effects can include neurological issues, such as tremors or seizures. Always monitor your dog closely during treatment and consult with your vet if you notice any adverse effects.

Evading the Immune Response: The Trophozoite-Tricksters

Giardia trophozoites are tricksters when it comes to evading your dog’s immune system. They’re constantly changing their surface proteins, making it difficult for the immune system to recognize and eliminate them. This makes an ongoing Giardia infection quite a challenge to resolve.

What To Feed Your Dog When They Have Giardia

Here’s the scoop on foods that can help restore balance and harmony in your dog’s system.

Garlic: The Scented Sentinel

Garlic may be known for its robust aroma, but this aromatic bulb plays more than just the flavor card. It’s also a potent antimicrobial. Allicin, a sulfur-containing compound in garlic, has impressive antimicrobial properties, making it a potent ally against Giardia. If you heard that it was toxic for dogs. You’re right but … it takes a ton of garlic for it to be unsafe. Read about it here.

Ginger: The Spicy Shield

Ginger, with its distinctive zing, is more than just a kitchen spice. It’s a natural antimicrobial powerhouse that can help curb Giardia’s growth. Its bioactive compounds, including gingerol and shogaol, are what make ginger an antimicrobial superfood.

Manuka Honey: The Sweet Soother

Manuka honey, particularly with an MGO (methylglyoxal) rating of over 400, is not your everyday honey. This liquid gold from Down Under has strong antimicrobial properties and aids in healing the gut lining damaged by Giardia. Just feed a drop per day for seven days.

Leafy Greens: The Verdant Virtuosos

Extra leafy greens like kale, collard greens and broccoli sprouts offer a nutrient-dense feast for your dog. These green virtuosos are loaded with fiber and antioxidants that can support gut health, making them an excellent addition to your dog’s post-Giardia menu. Add them as toppers to your dog’s meals. Leafy greens help your dog’s body return to homeostasis by activating the N2f2 pathways.

Put Fish on Pause

As we’ve learned, Giardia has a thing for lipids. So, for a while, it might be best to take fish off the menu. You can restart it about a week or two after Giardia is gone.

Pumpkin Seeds: The Petite Powerhouses

Don’t be fooled by their size; pumpkin seeds are petite powerhouses of nutrition. Rich in antioxidants and a good source of fiber, these tiny seeds can support gut health. Some studies also suggest they may have antiparasitic properties, making them a worthy addition to your dog’s diet.

A Journey To the East – Shiitake

Shiitake mushrooms are chock-full of beta-glucans, complex sugars that act like immune-system personal trainers. Beta-glucans are renowned for their ability to modulate and support the immune system, making it more efficient and responsive. They help to invigorate your dog’s immune cells, like macrophages and natural killer cells, enhancing their ability to seek out and neutralize threats like the Giardia parasite.

Lentinan, a specific type of beta-glucan found in Shiitake, is particularly noteworthy. Research shows that Lentinan can stimulate the immune system, helping it to mount a more effective defense against invaders.

Probiotics To The Rescue

Ah, the fantastic world of probiotics! These beneficial microorganisms often don’t get the credit they deserve for their crucial role in promoting gut health. Among these silent heroes, two stand out – Lactobacillus and Saccharomyces. Let’s delve into how they can help.

Lactobacillus – The Friendly Bacteria

Lactobacillus is a genus of bacteria that form part of your dog’s microbiome, the community of microorganisms living in their gut. These friendly bacteria serve a buffet of benefits.

Firstly, they compete with pathogens, like Giardia, for resources and attachment sites in the gut, essentially blocking the bad guys’ path. This phenomenon, known as competitive exclusion, can help reduce the number of harmful organisms in the gut.

Secondly, Lactobacillus strains produce various antimicrobial substances, including lactic acid, hydrogen peroxide, and bacteriocins, which inhibit the growth of harmful bacteria and parasites. Essentially, these friendly bacteria have a strong security system that keeps unwanted guests at bay.

Thirdly, they help restore the balance of gut flora post-infection. Remember, in a Giardia-infected gut, the bacterial balance is often disrupted. Lactobacillus helps reestablish this balance, nurturing gut health.

Saccharomyces – The Beneficial Yeast

Saccharomyces is a genus of yeast, with Saccharomyces boulardii being the most notable species used in probiotic supplements for dogs. These yeasts have shown promising results in managing gastrointestinal disorders.

Like Lactobacillus, S. boulardii also competes with pathogens for resources and space, creating a hostile environment for the likes of Giardia. Furthermore, this yeast produces substances that inhibit toxin activity, protecting the gut lining from damage.

S. boulardii has been shown to stimulate the production of IgA, an antibody that plays a crucial role in mucosal immunity. This helps to fortify the body’s defenses against invading pathogens.

Also, S. boulardii supports the growth of beneficial bacteria, contributing to the overall health of the gut microbiome.

Citrus Pectin – The Biofilm Buster

Citrus pectin is a type of fiber found in the peel and pulp of citrus fruits. It’s got a whole bunch of health benefits, but when it comes to Giardia, its role as a ‘biofilm buster’ shines bright.

Now, before we jump in, what exactly is a biofilm? It’s a protective layer that certain organisms, including Giardia, create around themselves for survival and to evade the host’s immune system. It’s like their fortress, providing protection from external threats and aiding in colonization and proliferation within the host.

Here’s where citrus pectin enters the picture. Citrus pectin has the unique ability to disrupt these biofilms, leaving the underlying organisms, like Giardia, more exposed and vulnerable to antimicrobial agents and the host’s immune response.

In addition, citrus pectin is a form of soluble fiber, which serves as food for beneficial gut bacteria. When the good bacteria feast on this fiber, they produce short-chain fatty acids, such as butyrate, which can further inhibit the growth of pathogenic organisms and promote gut health.

So, by incorporating citrus pectin into your dog’s diet, we’re not only launching a direct attack on Giardia’s protective shield but also supporting a healthy gut environment that’s less friendly to the parasite. Read more in citrus pectin HERE

Strengthening The Immune System for Immunity

Picture your dog’s immune system as a team of microscopic defenders, tirelessly working to keep harmful invaders, like the Giardia parasite, at bay. When your dog’s immune system is strong, it can mount an effective response against Giardia, helping to limit the parasite’s growth and influence in the body.

Now, don’t get me wrong. A robust immune system isn’t a magic answer that will instantly annihilate Giardia. This parasite is a crafty adversary. However, a well-functioning immune system can significantly contribute to the containment and eventual expulsion of Giardia from your dog’s body.

So, what can you do to support your dog’s immune system in this task?

First, ensure your dog is fed a balanced, nutritious real food diet and incorporate the ideas above. Quality nutrition is the bedrock of a well-functioning immune system. Foods rich in vitamins, minerals, and antioxidants can help boost immune health. The superfoods we talked about earlier, like garlic, ginger, Manuka honey, leafy greens, and pumpkin seeds, can certainly come into play here.

Secondly, regular exercise is key. Physical activity not only keeps your dog’s body fit but also supports a healthy immune system.

Lastly, minimizing stress and ensuring your dog gets plenty of rest are also important. Stress can suppress the immune system, while adequate rest allows the body to repair and rejuvenate itself.

The Bottom Line – When In Doubt Check It Out

If your dog is showing any signs of Giardia infection, it’s best to contact your vet promptly. A stool sample test can typically diagnose Giardia, and early treatment can help prevent more severe health issues.

Remember, each dog is unique and may not exhibit all these symptoms. Also, these signs can overlap with other health conditions, so it’s always best to seek professional advice.

Oftentimes prospective clients come to me thinking that their dogs have digestion issues when in fact it’s parasites and so if you’re experiencing ongoing diarrhea with weight loss, then go to your vet and rule out giardia.

As always, thank you for stopping by. I hope you found the information above on Giardia simple and easy to understand. I strive to explain things in a way that is more digestible. If you ever want to learn more, dive deep into the resources provided below. I wish you and your dogs Good Health!


Adam RD. Biology of Giardia lamblia. Clin Microbiol Rev. 2001 Jul;14(3):447-75. doi: 10.1128/CMR.14.3.447-475.2001. PMID: 11432808; PMCID: PMC88984.

Adam RD. Giardia duodenalis: Biology and Pathogenesis. Clin Microbiol Rev. 2021 Dec 15;34(4):e0002419. doi: 10.1128/CMR.00024-19. Epub 2021 Aug 11. PMID: 34378955; PMCID: PMC8404698.

Dashti N, Zarebavani M. Probiotics in the management of Giardia duodenalis: an update on potential mechanisms and outcomes. Naunyn Schmiedebergs Arch Pharmacol. 2021 Sep;394(9):1869-1878. doi: 10.1007/s00210-021-02124-z. Epub 2021 Jul 29. PMID: 34324017.

Tysnes KR, Skancke E, Robertson LJ. Subclinical Giardia in dogs: a veterinary conundrum relevant to human infection. Trends Parasitol. 2014 Nov;30(11):520-7. doi: 10.1016/j.pt.2014.08.007. Epub 2014 Sep 19. PMID: 25246022.

Tangtrongsup S, Scorza V. Update on the diagnosis and management of Giardia spp infections in dogs and cats. Top Companion Anim Med. 2010 Aug;25(3):155-62. doi: 10.1053/j.tcam.2010.07.003. PMID: 20937499.

Author Biography

Hannah Zulueta obtained her Certificate in Canine Nutrition from CASI Institute. She is also studying for her Doctorate in Acupuncture, Traditional Chinese Medicine, and Herbalism from the esteemed Pacific College of Health and Medicine.

She resides in San Diego with her three dogs, Maggie, Orbit, and Mr. Higgins.

She is available for one on one consultations. Additionally, you can find her sharing free content on Instagram.

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