Giardia in Dogs: What Every Guardian Needs to Know

Giardiasis is a common gastrointestinal infection in mammals, caused by Giardia duodenalis (also known as G. intestinalis or G. lamblia), a flagellated protozoan parasite found worldwide. It is the most prevalent protozoan in the human digestive system, affecting up to one billion people globally. While Giardia is often linked to diarrhea, some dogs can carry the parasite without showing symptoms. Highly contagious and difficult to eliminate, Giardia can pose a challenge for pet owners.

Understanding how Giardia spreads, how it’s diagnosed, and the available treatment options—both conventional and natural—is essential for protecting your dog’s health and preventing household contamination. In this article, we’ll cover everything you need to know about Giardia, including what to do if your dog repeatedly tests positive without symptoms and how to navigate different treatment approaches.

The parasite exists in two forms:

• Trophozoites: The active form that lives in the intestines and causes symptoms.
• Cysts: The dormant, hardy form that is excreted in feces and can survive in the environment for weeks to months.

Dogs contract Giardia by ingesting the cysts, usually from contaminated water sources, such as puddles, lakes, streams, or even infected dog bowls.

Humans can get Giardia by drinking contaminated water, eating contaminated food, or through direct contact with an infected person. While it’s possible to get it from animals, this happens very rarely.

The idea that Giardia can spread from pets to humans (zoonotic transmission) is debated. Certain types of Giardia (types A & B) are found in both humans and animals, but some experts believe pets get these from human contamination rather than the other way around. Other scientists argue that cross-species transmission may be more common than we think.

Since it’s hard to tell which Giardia type an animal has, it’s best to assume an infected pet could spread it to humans. 

• Good hygiene (especially washing hands after handling pet waste) reduces the risk.
• Children and people with weak immune systems are at higher risk and should avoid direct contact with infected animals.

While Giardia from pets is unlikely to infect humans, basic precautions can help keep everyone safe.

Some dogs show no symptoms at all, while others may experience:

• Watery, foul-smelling diarrhea that can be bloody
• Vomiting
• Weight loss
• Dehydration
• Loss of appetite
• Lethargy

When Giardia infects an animal, the parasite attaches to the walls of the intestine, damaging the cells that help with digestion. This can cause changes in how the gut works, leading to problems like poor nutrient absorption, digestive issues, and watery diarrhea. The damage to the intestine includes the flattening of the tiny finger-like projections (called villi) that normally help absorb food, making digestion even harder. This damage could take months to years to fully heal after the infection has been cleared.

Diarrhea in infected animals happens because the gut can’t properly digest or absorb food, and the intestines start producing extra fluid. Interestingly, diarrhea can start before the parasite is even shed in the stool. The timing of when Giardia cysts (the infectious stage) are passed in feces varies:

• Dogs: 5 to 12 days after infection
• Cats: 5 to 16 days after infection

Young puppies and kittens, animals with weak immune systems, and those with other stomach or intestinal diseases are more likely to show symptoms. However, many animals infected with Giardia don’t show any symptoms at all.

Not all Giardia infections are the same—some strains seem to cause worse symptoms than others, though scientists are still figuring out why. The severity of the infection may depend on several factors, including:

• The toxins produced by the parasite
• Disruptions to the balance of good bacteria in the gut
• Inflammation and irritation in the intestines
• Damage to digestive cells, leading to poor enzyme function
• The loss of protective gut lining, making the intestines more sensitive
• Increased fluid loss, leading to more severe diarrhea

Giardia is often diagnosed using the following methods:

• Fecal Float Test: Detects Giardia cysts in a stool sample under a microscope. A zinc sulfate fecal flotation test is best, as it preserves the parasite better than other methods. Spinning the sample (centrifugation) improves accuracy.
• ELISA (Enzyme-Linked Immunosorbent Assay) Snap Test: A more sensitive test that detects Giardia antigens.
• PCR Test: A highly accurate molecular test that detects Giardia DNA.

Because Giardia cysts are shed intermittently, a single negative test does not always mean a dog is free of infection. A single test may miss infections, as it only detects about 70% of cases. Multiple stool samples over several days may be required for accurate diagnosis in symptomatic patients.

The primary goal of treatment is to eliminate clinical symptoms. Elimination of giardial infection can be difficult, so cure is often considered a secondary goal. Organism elimination can be difficult because of resistance of some Giardia spp. Strains.

It is also important to rule out other causes of gastrointestinal symptoms. A study found that 27% of 142 dogs tested positive for Giardia, but infected dogs did not show significantly higher clinical scores or more gastrointestinal symptoms than uninfected dogs. The severity of clinical signs was not correlated with the number of Giardia cysts present, suggesting that other factors contribute to gastrointestinal issues in young dogs. The study emphasizes the importance of ruling out other gastrointestinal diseases rather than focusing solely on eliminating Giardia cysts.

Managing diarrhea:

Diet: A bland, easily digestible, gently cooked diet is recommended until stools are firm for 3 consecutive days. Ground turkey and canned, organic pumpkin is a great choice.

Fiber: Adding fiber to the diet may improve clinical signs by decreasing bacterial overgrowth and/or by preventing parasite attachment to microvilli. I use plain, organic psyllium husk. Dosing:: Breeds up to 20 pounds: one teaspoon twice daily, medium dog breeds up to 20-40 pounds: two teaspoons twice daily, and large dog breeds above 40 pounds: one tablespoon twice a day. Mix with warm water. This dose can be increased or decreased based on the severity of the diarrhea and response to treatment.

Microbiome Restorative Therapy: In chronically-infected patients or those that fail to respond to therapy, Microbiome Restorative Therapy™ (MBRT™) may be beneficial. MBRT™ contains healthy feces from a donor. It is administered orally or rectally to alter and improve GI flora.

Soil based Probiotics: Support gut health and immune function, making it harder for Giardia to thrive. Check out my blog on how to provide probiotics to your dog. It is important to provide probiotics and continued gut support after the giardia infection has resolved.

Conventional Dewormers

• Fenbendazole (Panacur): A broad-spectrum dewormer that treats Giardia in dogs by disrupting the parasite’s metabolism, preventing its ability to reproduce and survive in the intestines. Recommended dose is 50 mg/kg PO q 24 hrs for 3-5 days.

Metronidazole: A commonly prescribed antibiotic with antiprotozoal properties. However, resistance to this drug is increasing and this medication has negative effects on gut microflora. I personally do not use Metronidazole to treat giardia.
Combination Therapy: Some vets prescribe both medications together for stubborn infections.

*The giardia parasite is becoming resistant to many anti-protozoal drugs, which means more and more pets are becoming persistent carriers of the infection.

If you’re looking for a more holistic approach, these natural options may support conventional treatment or serve as a preventive measure:

• Seeds contain natural compounds that help expel parasites from your dog’s system:

1. 1. • Pumpkin Seeds: Rich in an amino acid called cucurbitin, which paralyzes parasites and helps remove them from the intestines. Give ¼ teaspoon per 10 pounds of body weight, once or twice daily, until parasites are gone.
      • Black Cumin Seeds: A well-known anti-parasitic food, black cumin seeds can be given whole. Toast them lightly to remove bitterness and add ½ to 1 teaspoon per day to your dog’s meals.

• Diatomaceous Earth (DE): Diatomaceous earth is a natural mineral that works by dehydrating and eliminating parasites from the digestive system. The key is using food-grade DE, not industrial-grade. Because this treatment can be abrasive to the gut it should be used with caution.

• Small dogs: ¼ teaspoon per day
• Medium dogs: ½ teaspoon per day
• Large dogs: 1 teaspoon per day

DE needs to be given daily for at least 7 days to kill adult worms and long enough to catch newly hatching eggs. However, it does not kill eggs directly, so extended use is necessary.

• Apple Cider Vinegar (ACV) Adding raw, organic, unfiltered apple cider vinegar to your dog’s food or water helps create a more alkaline environment in the digestive tract, making it less hospitable to parasites. The recommended amount is ¼ to 1 teaspoon per day, depending on your dog’s size.

• Herbal Remedies: Several herbs are known for their antiparasitic effects:

1. 1. • Coptis Teapills Coptis are all-natural Chinese herbal caps made from Huang Lian Su Wan, a bitter, cool herb used to drain heat and relieve toxicity from the lower body. ( contains Coptis chinensis, or Chinese goldthread) which have natural antimicrobial and anti-inflammatory properties. Berberine, the active compound, is sometimes used as a natural alternative for treating infections, including Giardia. Here is a product I trust.
      • Goldenseal (Hydrastis canadensis) contains berberine, a natural antimicrobial compound that has been studied for its effectiveness against Giardia and other protozoan parasites. A study in Revista de Investigación Clínica found that 14 plant extracts were tested in vitro against Giardia, and Goldenseal showed significant antigiardial activity.
      • Oregon Grape also contains berberine, similar to Goldenseal, and has been used interchangeably by herbalists to treat protozoal infections, including Giardia. Research suggests that berberine from Oregon Grape root is effective against several parasites, including Giardia, by disrupting their DNA replication.
      • Garlic (in small amounts): Garlic is known for its natural antiparasitic properties, but it must be used in moderation. The proper dosage is ¼ clove per 10 pounds of body weight daily. To maximize its benefits, chop the garlic and let it sit for 10-15 minutes before adding it to your dog’s food. However, garlic should be avoided in pregnant or nursing dogs.

• Coconut Oil: Lauric Acid, a Component of Coconut Oil, Shows Antigiardial Effects. A study found that lauric acid, a medium-chain fatty acid found in coconut oil, had an effect against Giardia lamblia in an experimentally infected hamster model. Lauric acid was observed to reduce Giardia parasite counts and improve the intestinal health of infected subjects. My favorite coconut oil is by cocotherapy.

6. Fruits & Vegetables

Certain fruits and vegetables act as natural dewormers due to their high fiber and enzyme content. These help expel parasites from the digestive tract:

• Carrots, Bananas, Apples, Coconut, and Papaya: These fiber-rich foods support gut health and act as gentle, natural dewormers. Simply grate or chop them and mix them into your dog’s food. A general guideline is 1 teaspoon per 10 pounds of body weight.
• Fermented Vegetables: These boost gut health and strengthen the immune system while also aiding in parasite elimination.

7. Homeopathic and Essential Oil Remedies

There are a variety of homeopathic and herbal products designed to support your dog’s natural defenses against parasites. Always choose high-quality, well-reviewed products from reputable sources. Some essential oils, such as oregano oil and neem oil, may also have antiparasitic properties, but they must be used with caution and under the guidance of a holistic veterinarian.

If your pet was successfully treated for Giardia but still tests positive on the IDEXX Giardia SNAP test, don’t panic! This can happen for a few reasons, and it doesn’t always mean the infection is still active.

1. False Positive Result

The SNAP test is highly accurate (95% sensitivity, 99% specificity), but no test is perfect. Sometimes, if the chance of disease is very low, the test may give a false positive result.

2. Your Pet is a Carrier (But Not Sick)

Even after treatment, some pets carry Giardia without symptoms. Instead of completely clearing the parasite, it may stay in the intestines as part of the gut bacteria. This is more common in cats, where studies show up to 80% of healthy cats may have Giardia without symptoms. If your pet isn’t showing any signs of illness, this may not be a concern.

3. Reinfection

Giardia is easy to catch again, especially if cysts are still in the environment (like contaminated water, shared pet spaces, or bedding). If your pet was recently treated but re-exposed, the test could be picking up a new infection.

4. SNAP Test Detects Antigens, Not Active Infection

Even if Giardia is gone, the SNAP test may still detect leftover antigens in the body for weeks or even months. This means a positive test doesn’t always mean the parasite is still there.

Should You Retest After Treatment?

No, unless your pet has symptoms again. Retesting can be misleading, as some successfully treated pets stay antigen-positive for months. Instead of relying on the SNAP test, watch for symptoms. If needed, alternative lab tests (PCR) can confirm if Giardia is truly gone.

Bottom Line: If your pet is healthy and symptom-free, there’s no need to keep testing!

The best way to prevent parasites is by maintaining a strong immune system and a clean living environment for your dog. Here’s how:

✅ Boost the Immune System: A strong immune system helps keep parasites in check. Medicinal mushrooms, antioxidants, pre and probiotics support your dog’s microbiome and overall health. Monitor and manage your dog’s microbiome through regular testing using animalbiome.com.

✅ Provide a Balanced Diet: Feed a species-appropriate, high-quality fresh diet to ensure your dog gets all the necessary nutrients to fight off infections naturally.

✅ Maintain Good Hygiene: Pick up and dispose of feces promptly, disinfect food and water bowls regularly, and keep your dog’s bedding clean. Wash your hands after cleaning up after your pet and after petting if your dog is infected. Bathe dogs after treatment to remove lingering cysts from their fur.

✅ Keep the Yard Clean: Parasites thrive in moist environments. Regularly remove waste from your yard, and consider using natural repellents like nematodes to control parasite eggs in the soil.

✅ Schedule Routine Vet Checkups: Regular fecal testing is essential for detecting parasites early. Have your vet check stool samples at least once a year, or more often if your dog spends a lot of time outdoors.

 ✅ Avoid letting your dog drink from puddles, lakes, or shared water bowls at dog parks. Stagnant water is the most common source of giardia infections. Giardia cysts are incredibly resilient, capable of surviving in cold water for months. This allows them to persist in lakes, streams, and even drinking water supplies, making waterborne outbreaks a major concern worldwide.

Giardia can be a frustrating parasite for dog guardians, but with the right knowledge and preventive measures, it can be managed effectively. Whether you choose conventional medications, natural remedies, or a combination of both, the key is to focus on your dog’s overall health, a fresh diet, proper hygiene, and a clean environment. If your dog tests positive without symptoms, stop testing them (I’m serious). By staying informed, you can take precautions to help prevent guardian diagnosis and if your dog develops giardia you now know how to handle it. 

1. Can Giardia be transmitted to humans?

Yes, but it is rare for humans to contract Giardia from infected dogs. To help avoid this, always wash your hands after handling dog waste and avoid direct contact with infected stool.

2. Should I keep my dog isolated if they have Giardia?

If you have multiple dogs, it’s best to keep an infected dog separate and disinfect shared spaces. However, if all dogs are exposed, treating them simultaneously may be necessary.

3. How long does Giardia last?

With treatment, Giardia typically clears within 1-2 weeks. However, reinfection can occur if the environment isn’t properly disinfected.

4. Should I use both conventional and natural treatments together?

In some cases, a combination approach works best. If your dog has a severe infection, conventional dewormers may be necessary initially, but you can support recovery with natural remedies and immune boosters.

5. My dog tested positive but has no symptoms. Should I treat them?

This depends on your vet’s recommendation. I, personally, would not treat these cases with conventional dewormers. I would likely add some natural remedies, test the gut microbiome and monitor for clinical symptoms. If there are immune-compromised people or children in the household then treatment may be elected.

6. Should I monitor therapy with additional Giardia testing?

Giardia testing is currently recommended only for initial diagnosis of giardiasis. Patients who have been successfully treated, with resolution of clinical signs, do not need follow-up monitoring tests unless the owner is immunocompromised and at higher risk for zoonotic infection.

7. What do I do if my dog’s symptoms do not resolve or if they recur?

Monitoring patients who have failed treatment, or have relapsing signs is more complicated. Treatment failure may occur as a result of re-exposure and re-infection, or as a result of ineffective medical therapy. Currently available tests cannot differentiate between these two possibilities. Re-exposure can occur rapidly (the pre-patent period for Giardia in cats is as short as 4-5 days), and clinical signs can occur within 2 weeks of stopping therapy. So, if you have other pets in the household you must be sure that everyone has been tested and treated.

This blog along with many others sprang out of a question asked during our weekly pack chat inside our exclusive membership: The Dog Mom Society.

Click below to learn more about our beautiful community of like-minded dog guardians who prioritize their dog’s health and wellness.

1. Ballweber, L. R., Xiao, L., Bowman, D. D., Kahn, G., & Cama, V. A. (2010). “Giardiasis in Dogs and Cats: Update on Epidemiology and Public Health Significance.” Trends in Parasitology, 26(4), 180-189. DOI: 10.1016/j.pt.2010.01.005
2. Thompson, R. C. A., & Smith, A. (2011). “Zoonotic Potential of Giardia.” International Journal for Parasitology, 41(9), 925-938. DOI: 10.1016/j.ijpara.2011.05.009
3. Ryan, U., & Hijjawi, N. (2015). “Genetics and Transmission of Giardia.” Experimental Parasitology, 151-152, 25-31. DOI: 10.1016/j.exppara.2015.02.002
4. Wright, J. M., Dunn, L. A., Upcroft, P., & Upcroft, J. A. (2003). Efficacy of antigiardial drugs. Expert Opinion on Drug Metabolism & Toxicology, 2(6), 529-541. DOI: 10.1517/14740338.2.6.529
5. (Hehl, A. B. (2018). Five facts about Giardia lamblia. PLoS Pathogens, 14(9), e1007250. DOI: 10.1371/journal.ppat.1007250)
6. (Carmena, D. (2023). High Diversity of Giardia duodenalis Assemblages and Sub-Assemblages in Asymptomatic School Children in Ibadan, Nigeria. Tropical Medicine and Infectious Disease, 8(3). DOI: 10.3390/tropicalmed8030152)
7. Reference: (El Naggar, H. M., Mohammed, B. O. (2023). Study on the Therapeutic Effect of Coconut Oil Extracts as an Alternative Medicinal Plant in Cryptosporidium Infected Mice. Türkiye Parazitoloji Dergisi. Link)
8. Reference: (Maisa, S. A., Samar, A. S., Shaimaa, H. E., & Soheir, M. S. (2013). Therapeutic effect of lauric acid, a medium-chain saturated fatty acid on Giardia lamblia in experimentally infected hamsters. BVS Salud. Link)