# How Do Cats Get Giardia? Causes and Prevention Giardia in cats: how do they get it? Most cats pick up this intestinal parasite by swallowing microscopic cysts from contaminated water, food, soil, or surfaces, including litter boxes and outdoor areas where infected animals have defecated. The parasite then settles in the small intestine, where it can cause diarrhea or no signs at all. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Giardia spreads by the fecal-oral route, meaning a cat swallows cysts shed in the feces of an infected animal, often through water, food, or contaminated surfaces [1]. - Outdoor access, stray contact, and group housing raise the risk, and adult or free-roaming cats in one study were significantly more likely to test positive than kittens or indoor-only cats [2]. - Many infected cats have no diarrhea at all, so a positive test does not always mean the parasite is causing the symptoms you see [2]. - Diagnosis usually involves finding cysts or antigens in stool samples, and because shedding comes and goes, your veterinarian may need more than one sample [3]. - Treatment is prescription antiparasitic medication chosen by your veterinarian, along with thorough cleaning of the environment, which is an essential part of control [3]. ## What Is Giardia in Cats? Giardia is a single-celled parasite, called a protozoan, that lives in the intestine. The type that infects cats and other mammals is Giardia duodenalis, also known as Giardia intestinalis or Giardia lamblia [4]. It exists as a species complex made up of different genetic groups, called assemblages, that tend to show host specificity [3]. That last point matters for owners. Cats are most often infected with assemblages that are adapted to cats and dogs, while the assemblages most commonly found in people (A and B) show up less often in cats [1][5]. This is one reason zoonotic transmission, meaning spread from pets to people, appears to happen relatively rarely [3]. The parasite has two life stages that matter. The active form, called a trophozoite, attaches to the lining of the small intestine. The dormant form, called a cyst, is passed in feces and can survive in the environment long enough to infect the next animal that swallows it [1]. ## Signs Owners Notice The classic sign of giardiasis is diarrhea, often with pale, greasy, foul-smelling stool that may contain mucus [3]. Some cats have soft stool that comes and goes for weeks. Others have abdominal discomfort or seem to strain. Here is the confusing part. A large share of infected cats look completely normal. In one study of 272 cats, every cat that tested positive for Giardia had no diarrhea at all [2]. So a cat can carry and shed the parasite without you ever noticing a problem. Kittens, senior cats, and cats with other illnesses may show more obvious signs because their immune systems handle the infection less well. If your cat has loose stool with mucus, several conditions can look similar, including inflammatory bowel disease and food intolerance. Our guide to [loose stools with mucus in cats](/knowledge/veterinary-medicine/symptom-guides/why-is-my-cat-having-loose-stools-with-mucus-ibd-vs-giardia-vs-food-intolerance) walks through how veterinarians sort these apart. ## Giardia in Cats Causes: How Cats Actually Get Infected This is the heart of the question. Giardia in cats causes infection through one main route: swallowing cysts. Everything else is about where those cysts come from. ### Contaminated Water Standing water is a common source. Ponds, puddles, birdbaths, and outdoor bowls that collect rain can hold cysts from infected animals [1]. Cats that drink from these sources take in the parasite directly. Even indoor water bowls can become contaminated if they are shared with other pets or left dirty for long periods. ### The Litter Box A shared litter box is one of the most overlooked sources in multi-cat homes. An infected cat sheds cysts in feces, and those cysts can contaminate the box, the scoop, and the floor around it. If another cat steps in the box and later grooms its paws, it can swallow cysts. This is why litter box hygiene matters so much when one cat in the house tests positive [3]. ### Food and Prey Cysts can contaminate food, either through dirty bowls or through prey. Cats that hunt mice or other small mammals may be exposed, since Giardia infects many wild mammals and birds worldwide [3]. Outdoor cats that hunt have more chances to encounter the parasite than indoor cats do. ### Soil and Outdoor Surfaces Cysts survive in cool, damp soil and on surfaces where infected animals have defecated. A cat that walks through contaminated ground and then grooms can infect itself. Gardens, sandboxes, and areas where strays roam are all potential sources. ### Contact With Other Cats Group housing, shelters, catteries, and homes with several cats make transmission easier. In a study of 500 stray cats living at temples in Bangkok, the overall prevalence of Giardia was 10.8% [6]. Crowded conditions with shared food, water, and litter areas give the parasite more chances to move between animals. ### Risk Factors That Raise the Odds | Risk factor | Why it matters | |---|---| | Outdoor access | More contact with contaminated water, soil, and prey [3] | | Living with other cats | Shared litter boxes and bowls spread cysts easily | | Being an adult cat | Adults had about 5.3 times the odds of infection compared with kittens in one study [2] | | Free-roaming or stray status | Non-domiciled cats had about 8.6 times the odds compared with owned cats [2] | | Weakened immunity or stress | Makes signs more likely to appear | Prevalence varies widely by location. In a Polish study, Giardia cysts were found in 7.06% of cat fecal samples [4]. In the Brazilian study mentioned above, 74.63% of cats tested positive, which the authors described as the highest prevalence ever identified in cats in Brazil [2]. These numbers differ because of climate, housing, stray populations, and testing methods, not because the parasite behaves differently. ## How Veterinarians Diagnose Giardia Diagnosis starts with a stool sample. Veterinarians look for cysts under a microscope or test for Giardia antigens in the feces [3]. Both approaches are used, and in one comparison, the two methods agreed almost perfectly [2]. Timing matters. Cats shed cysts in waves, so a single sample can miss the infection. Your veterinarian may ask for samples collected on two or three different days. A fecal test that comes back negative does not always rule Giardia out. Your veterinarian will also ask about your cat's history: outdoor access, other pets, recent boarding, and whether the diarrhea has been intermittent. Ruling out other causes of chronic diarrhea is part of the process, since Giardia is not the only parasite or condition that produces loose stool. For a broader look at intestinal worms and protozoa in pets, see [intestinal parasites in dogs and cats](/knowledge/veterinary-medicine/parasitic-diseases/intestinal-parasites-in-dogs-and-cats). ## Treatment Options for Giardiasis Treatment usually combines medication with cleaning. Both parts matter. ### Medication The most common drugs are nitroimidazole derivatives such as metronidazole and secnidazole [7]. Your veterinarian calculates the dose from your cat's weight and health status, and the exact regimen varies by patient [3]. Never use leftover medication from another pet or a human prescription. Some veterinarians repeat treatment or switch drugs if signs persist. Treatment regimens are variable and depend on the specific situation [3]. If your cat does not improve, tell your veterinarian instead of waiting it out. ### Environmental Cleaning Cleaning is not optional. Hygiene measures are an essential component of control [3]. Cysts are tough and can linger on surfaces, so you will want to: - Scoop litter boxes daily and wash them with hot water and detergent regularly. - Replace litter completely during treatment, since cysts can survive in used litter. - Wash food and water bowls daily with hot, soapy water. - Clean bedding, toys, and carriers. - Bathe your cat if it has diarrhea, since cysts can cling to fur around the rear end. - Wash your hands after handling litter, stool, or soil. If you have more than one cat, talk with your veterinarian about whether the other cats should be tested. For a deeper look at household spread and cleaning steps, see [Giardia in cats: zoonotic risk and sanitation protocol](/knowledge/veterinary-medicine/parasite-control/giardia-in-cats-zoonotic-risk-and-sanitation-protocol). ## Recovery, Outlook, and Long-Term Management Most cats respond well to treatment, and diarrhea typically improves within days to a couple of weeks. Some cats clear the infection on their own, and some continue to shed cysts without signs [2]. Because of that, a follow-up fecal test after treatment is often recommended to confirm the parasite is gone. Reinfection is common if the environment is not cleaned or if your cat goes back outside to the same contaminated areas. Long-term management usually means: - Keeping litter boxes clean and providing one box per cat, plus one extra. - Limiting access to standing water outdoors. - Keeping bowls and bedding clean. - Testing new cats before introducing them to the household. - Rechecking stool if diarrhea returns. Cats with ongoing digestive issues may need a longer conversation with your veterinarian about other causes. Chronic diarrhea in older cats can have several explanations, and some are unrelated to parasites. ## Prevention: Reducing the Risk You cannot remove every possible source of Giardia, but you can lower the odds. - Provide fresh, clean water indoors and change it daily. - Do not let your cat drink from puddles, ponds, or outdoor containers. - Scoop litter boxes at least once a day. - Wash bowls and litter boxes with hot water and detergent on a regular schedule. - Keep indoor cats indoors, which cuts exposure to contaminated soil, water, and prey. - Quarantine and test new cats before mixing them with resident cats. - Wash your hands after cleaning litter boxes or gardening. - Keep your cat's immune system in good shape with routine veterinary care. If your cat is diagnosed with Giardia, treat the whole household routine as part of the cure. Medication clears the parasite in the gut, and cleaning stops it from coming back. ## Limitations and When to Contact a Veterinarian This article gives general information, but every cat is different. Your veterinarian needs to examine your cat and run tests to make a diagnosis and set a treatment plan. Contact your veterinarian the same day if your cat: - Has diarrhea lasting more than 24 to 48 hours. - Has blood in the stool or black, tarry stool. - Is vomiting repeatedly or cannot keep water down. - Seems painful when you touch the belly. - Is a kitten, senior, or has a chronic illness and develops diarrhea. Seek emergency care now if your cat: - Is weak, collapsed, or unresponsive. - Has pale gums or trouble breathing. - Shows signs of severe dehydration, such as tacky gums, sunken eyes, or skin that stays tented when gently pinched. - Has not eaten or drunk for more than 24 hours. Schedule a routine visit if your cat has soft stool that comes and goes, has been treated for Giardia before and symptoms return, or lives with other cats and one has tested positive. ## Frequently Asked Questions ### Can I catch Giardia from my cat? It is possible but uncommon. Cats are usually infected with host-adapted assemblages, and zoonotic transmission seems to occur relatively rarely [3]. Still, wash your hands after handling litter or stool, especially if anyone in your home has a weakened immune system. ### Do all cats with Giardia have diarrhea? No. In one study, every cat that tested positive had no diarrhea at all [2]. Cats can carry and shed the parasite while looking completely healthy, which is one reason testing matters in multi-cat homes. ### How long does Giardia survive in the environment? Cysts are built to last and can remain infectious in cool, damp conditions for a meaningful period, which is why surface cleaning is part of treatment [1]. Heat and drying reduce their survival, so hot water and thorough drying help. ### Should I treat my other cats if one tests positive? Ask your veterinarian. Because cats in the same home share litter boxes and bowls, testing the others is often reasonable, but treatment decisions depend on each cat's test results and health. ### Can Giardia come back after treatment? Yes, reinfection is possible if your cat returns to a contaminated environment or if cleaning was incomplete. A follow-up fecal test and consistent litter box hygiene lower that risk [3]. ## Related Articles - [Giardia in Cats: Zoonotic Risk and Sanitation Protocol](/knowledge/veterinary-medicine/parasite-control/giardia-in-cats-zoonotic-risk-and-sanitation-protocol) - [Intestinal Parasites in Dogs and Cats: Signs and Prevention](/knowledge/veterinary-medicine/parasitic-diseases/intestinal-parasites-in-dogs-and-cats) - [Why Is My Cat having loose stools with mucus? IBD vs Giardia vs Food Intolerance](/knowledge/veterinary-medicine/symptom-guides/why-is-my-cat-having-loose-stools-with-mucus-ibd-vs-giardia-vs-food-intolerance) - [Why Do Older Cats Get Kidney Disease](/knowledge/veterinary-medicine/clinical-methods/why-do-older-cats-get-kidney-disease) - [What Can Cause A Urinary Tract Infection In A Cat](/knowledge/veterinary-medicine/clinical-methods/what-can-cause-a-urinary-tract-infection-in-a-cat) - [Why Does My Cat Have Gas?](/knowledge/veterinary-medicine/nutrition/why-does-my-cat-have-gas) - [Giardia in Cats: Treatment and Home Care](/knowledge/veterinary-medicine/parasitic-diseases/giardia-in-cats-treatment) - [Is Giardia in Cats Contagious to Other Cats?](/knowledge/veterinary-medicine/parasitic-diseases/giardia-in-cats-contagious) - [Can Cats Spread Giardia to Dogs? What Owners Need to Know](/knowledge/veterinary-medicine/parasitic-diseases/can-cats-spread-giardia-to-dogs) - [Feline Giardiasis: Diagnostic Challenges and Updated Treatment Protocols](/knowledge/parasites/pet-parasites/feline-giardiasis-diagnostic-challenges-treatment-protocols) ## References 1. [Molecular characterization and zoonotic potential of Giardia and Cryptosporidium infections in dogs and cats in Central Spain](https://pubmed.ncbi.nlm.nih.gov/42381722/). Food and waterborne parasitology, 2026. 2. [High prevalence of Giardia spp. in cats without diarrhea and agreement between diagnostic techniques in the municipality of Londrina, Paraná, Brazil](https://pubmed.ncbi.nlm.nih.gov/42474547/). Veterinary research communications, 2026. 3. [Giardiasis in Animals - Digestive System](https://www.merckvetmanual.com/digestive-system/giardiasis-giardia/giardiasis-in-animals). Merck Veterinary Manual. 4. [Prevalence of Giardia duodenalis genetic assemblages isolated from dogs and cats in Poland](https://pubmed.ncbi.nlm.nih.gov/41064408/). Journal of veterinary research, 2025. 5. [Comparison of multilocus genotyping and a commercial beta-giardin qPCR assay for detection of Giardia duodenalis zoonotic assemblages in cat and dog samples](https://pubmed.ncbi.nlm.nih.gov/41952221/). Parasites & vectors, 2026. 6. [Molecular detection and genetic characterization of Giardia duodenalis in temple stray cats in Bangkok, Thailand](https://pubmed.ncbi.nlm.nih.gov/42812357/). Frontiers in parasitology, 2026. 7. [Omeprazole as a Novel Treatment Option for Giardiasis in Cats](https://pubmed.ncbi.nlm.nih.gov/42035445/). Veterinary medicine and science, 2026. ## Further Reading - [Disorders Caused by Protozoa of the Digestive System in Cats - Cat Owners (Merck Veterinary Manual)](https://www.merckvetmanual.com/cat-owners/digestive-disorders-of-cats/disorders-caused-by-protozoa-of-the-digestive-system-in-cats) - [Gastrointestinal Parasites of Cats - Cat Owners (Merck Veterinary Manual)](https://www.merckvetmanual.com/cat-owners/digestive-disorders-of-cats/gastrointestinal-parasites-of-cats) - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners)