Giardia is a very common (worldwide) cause of digestive upset in cats. Lots of cats infected with Giardia shed their infective cysts but don’t show any symptoms. When symptoms do arise, occasional or ongoing abnormal stools (soft stool or diarrhea) are most common. Special testing (Giardia by ELISA and/or Giardia by PCR) is needed to reliably detect these microscopic protozoa. Giardia by ELISA is a very reliable test and used for both normal or abnormal appearing stools. Many veterinarians recommend including Giardia by ELISA (ClueJay Cat Stool Test Level 2) every time a cat stool is examined. For cats with ongoing (chronic) abnormal stools, including a Giardia by PCR (ClueJay Cat Stool Test Level 3) is an additional way to detect Giardia infections.
Giardia infection is very common in cats. While cats don’t always show signs of illness, infection can lead to poor absorption of food, soft stool or diarrhea.
Companion Animal Parasite Council (CAPC)
All About Giardia
Giardia are parasites that can inhabit and damage the intestines of many animals, including cats, dogs and people. Like coccidia, Giardia are protozoa and not “worms”. Neither are susceptible to “deworming” medications used for roundworms, hookworms, tapeworms, or whipworms.
Giardia have tails (called flagella) and form cysts while coccidia are tailless and form spores (oocysts). Both are single-celled parasites capable of infection and shedding without causing symptoms. With the naked eye you won’t ever see Giardia (or coccidia) in your cat’s stool. This is because all stages of their life are microscopic.
There is only one species of Giardia important in cats and people (Giardia duodenalis), which goes by several names: G. duodenalis, G. lamblia, G. intestinalis, or G. enterica.[3,6,7] Subtypes (genotypes) of Giardia duodenalis are called “assemblages” (from A to G). Cats most commonly become infected with Giardia subtype F.[3,4,6]
Giardia infection is worldwide and common in most types of domestic and wild mammals, many birds, and people. It is a common intestinal parasite of cats. Since many cats shed Giardia cysts into the environment without showing any symptoms, uninfected cats can pick up Giardia from infected cats through housing (shelters, kennels, catteries) or outdoor exposure. Thus Giardia infection is more likely for cats housed together (catteries), socialized with other cats, or sharing litterboxes. There are areas of the U.S. where Giardia infections are more common, but it is essentially everywhere.
While Giardia is common, finding it under the microscope isn’t. Only very occasionally are the Giardia cysts or motile trophozoites identified in a normal cat stool test (fecal ova and parasites). Most of the time, Giardia cyst antigen by ELISA (ClueJay Cat Stool Test Level 2) and/or Giardia by PCR (ClueJay Cat Stool Test Level 3) is needed to detect the presence of this parasite in cat stool.
Giardia are not viruses, bacteria or worms. They are protozoa that take on two forms: a motile, feeding trophozoite and a hardy, infective cyst. Both forms are very difficult to find under the microscope so it’s best to search for Giardia using special test techniques (ClueJay Cat Stool Test Level 2 or 3).
Trophozoites are the feeding form of the parasite that lives within the cat (“troph” means nourishment and “zoon” means animal). In certain orientations under the microscope, Giardia trophs are shaped like teardrops or tennis rackets with what appear to be “eyes”. The eyes are a pair of nuclei (containing the genetic material). Attached to the teardrop are four pairs of thin, whip-like tails called flagella, which are used like small propellers to swim. One side of the troph is pushed in (concave) to form an adhesive, sucking disk used to attach to and feed on the small intestine of the cat.
Giardia trophs are not designed to survive outside of the cat. If passed in the stool they quickly (within 30 minutes) die and decompose, so are only rarely seen in typical stool test preparations (fecal ova and parasite test). For protection, the trophs enclose themselves in an elliptical cyst before passing into the stool. While the cysts can occasionally be seen in an O&P (ova and parasite) stool preparation, this is not a reliable method for finding them. The cysts are transparent and very, very small. They are much smaller than worm eggs and even smaller than coccidia spores. Even more challenging, the tiny cysts look different when there is just one versus two trophs within the cyst (two “eyes” versus four “eyes”), or if damaged (half-moon appearance). Often Giardia cysts can’t be distinguished from yeast or plant pollen with certainty. Therefore, special testing (ELISA or PCR) is used to reliably test for the presence of Giardia.
Giardia infections don’t always cause symptoms in cats but when they do, occasional or ongoing soft stool or diarrhea is the most likely sign. Diarrhea from Giardia may appear soft, frothy, greasy, with mucus and foul-smelling odor.[4,5,6] It isn’t usually watery or bloody. However, giardiasis (infection from Giardia) should be considered when any cat or kitten has abnormal stool.
Lots of cats carry and shed Giardia while being otherwise healthy. The damage to their intestines is mild enough (likely from a low number of Giardia trophozoites) that no symptoms appear. While they risk spreading the infection to other cats through stool (sharing litterboxes), they may remain healthy even without treatment. [2,3,4]
Some longer-term Giardia infections can cause serious harm to the cat or kitten. The presence of high numbers of feeding trophs, plus the toxins they produce, and inflammation from the cat’s own immune response can result in considerable damage to their small intestine. The damage prevents the cells of the intestine from digesting and absorbing nutrients normally. This can lead to ongoing or occasional soft stools or diarrhea, poor coat appearance, weight loss, and sometimes vomiting.[1,2,6] In very severe cases, giardiasis can lead to debilitation and death.[1,2]
Giardia duodenalis cysts contaminate the indoor or outdoor environment from the stool of an infected cat. With humidity and moisture (dampness), Giardia cysts can survive for weeks to months indoors within a cattery, kennel, shelter, or household, or outdoors in soil, grass, or standing water.[1,4,6] Giardia is usually more common in areas with a high number of cats, including catteries, kennels, and shelters.[3,5]
Cats become infected or re-infected by accidently swallowing the giardia cysts.[1,2,3,5,6] The cysts are ingested from eating soil (self-grooming), grass or plants, or drinking water that had been contaminated with cysts.[1,3] Since Giardia cysts are infectious immediately upon passing in the stool, cats can also easily pick up infections from mutual grooming, or even by self-grooming after using a shared litter box.
Cats and kittens that are immune-suppressed, fighting off other infections, getting regularly re-infected with Giardia, and/or in stressful conditions (like being transported/relocated or housed in groups) are more likely to get sick with giardiasis (diarrhea, weight loss).
The life cycle of Giardia duodenalis is relatively simple, especially when compared to other protozoa like coccidia. There are only two forms of Giardia: a hardy, infective cyst and a feeding trophozoite. The “troph” is the motile form found in the small intestines of the cat while the cyst is the infective form of the troph used for “safe travel” in the environment.
When a cat (or other animal) swallows a Giardia cyst, typically two single-celled trophozoites emerge. They use their flagella “tails” to swim to the inside wall of the small intestines and attach using their concave sucking discs. They don’t enter the intestinal cells like coccidia or pass through the intestinal walls like roundworm larvae. They just attach, suck nutrients, and produce toxins which damage the intestinal cells and their brush-like villa (hairs).[3,4] The damage to the intestinal cell villa results in poor food digestion and absorption by the cat or kitten. Within the small intestines the trophs multiply their numbers by simply duplicating themselves (binary fission).[3,4]
Trophs are too fragile to survive in stool or water outside the cat and decompose quickly. This form is only sometimes seen in watery stool or diarrhea when immediately examined under a microscope. Trophs are not infectious to other cats or re-infective to the same cat. The way giardia trophs survive outside of the cat and transmit infection is by encysting.[3,4] Essentially the troph covers itself in a protective, immobile cocoon called a cyst. Shedding of these hardy cysts by the infected cat is intermittent but can go on for days or weeks at a time. The cysts are immediately infective and can survive in the environment for days, weeks, or even 1-3 months (especially with moisture and cool temperatures). Thus catteries, kennels, shelters, and home environments can become and stay contaminated with Giardia cysts with continued shedding by infected cats.
Human infection of Giardia (giardiasis) is common worldwide and sometimes called “Traveler’s Diarrhea” or for outdoor enthusiasts, “Beaver Fever”. It is usually transmitted through contaminated (human feces) drinking water, recreational water (swimming), or uncooked food. To avoid infection, it is best to avoid drinking from an untrusted source.[3,4]
There are seven subtypes (genotypes) of Giardia which infect animals. The Giardia subtype that typically infects cats (subtype F) is generally only infective to cats, while the subtypes known to infect dogs (subtypes D and F) are usually only infective to dogs. For people, subtypes A and B are the most common infective forms.
Since the subtype of Giardia infecting cats is different from the subtypes for people, the risk of humans getting giardiasis from a cat is extremely small.[1,3,7] However since transmission may be possible, people should practice good hygiene (washing hands; avoiding contact with cat stool) around cats that carry Giardia. This is especially true for people that have compromised immune systems and are more susceptible to infections. If your cat had carried or does carry Giardia and you or a family member that interacts with the cat becomes sick with intestinal problems, then be sure to tell the human healthcare professionals. While the risk for humans getting giardiasis from a cat is low, it isn’t zero.
Even with good hygiene, Giardia infections are quite common and probably the most common intestinal parasite of cats. Cats become infected by swallowing the Giardia cysts.[1,3] Since Giardia cysts are infectious immediately upon passing in the stool, cats can easily pick up infections from mutual grooming, or even by self-grooming after using a shared litter box.
Try to prevent your cat from eating grass or plants where other cats frequent; or drinking from water (puddles) that could have been contaminated with Giardia. Giving your cat constant access to fresh, clean water and quickly picking up and properly disposing of cat stool are the two most practical ways to prevent Giardia infections. Although preventive measures are helpful, infections are still possible. For this reason, it’s recommended that adult cats have their stool tested 1 to 2 times a year for Giardia, and up to 4 times in the first year for kittens.
Most veterinarians will recommend treating cats infected with Giardia when symptoms like soft stools or diarrhea are present. Sometimes for mild symptoms the treatment is simply supportive, like switching the cat temporarily to a bland home diet or prescription diet. If the symptoms are worse or not resolving, veterinarians may also prescribe medication targeting the disease-causing Giardia trophozoites.
Many veterinarians will also encourage owners to treat Giardia infected cats without symptoms. This is the same medical approach (treating even if symptoms aren’t present) typically used for roundworms, hookworms, tapeworms, whipworms, and coccidia. The rationale for this is threefold: parasite infections can worsen over time and lead to symptoms and disease, cats with intestinal parasites can be expected to shed them in their stools and risk infecting other cats, and some parasites can infect and harm people. These are all sensible reasons to try and eliminate Giardia infections in cats, even if the cat doesn’t have symptoms at the time of diagnosis.
However, not all veterinarians recommend treating Giardia infections in cats without symptoms. One reason is because many cats carrying Giardia don’t show any signs of illness. In these cases, the cat’s immune system is probably keeping the infection under control. Another reason is that medication side effects can (rarely) occur. There are currently no FDA-approved medications to treat this parasite in the U.S. and response to treatment (elimination of Giardia) isn’t always successful. This is most likely because the cat remains in an environment where re-infection keeps occurring, but not always. Other considerations for treatment failure are poor immune response, drug resistance, or the trophozoites are in the gallbladder or ducts of the pancreas where the medication is less effective.
Getting ahead of a Giardia infection can be a tough task with multiple cats, especially in a cattery, multi-cat household, or shelter. Regularly disinfecting these indoor environments can help kill the cysts. Use chlorine bleach (at 1:32 or 1:16 dilutions, or 1-2 cups in a gallon of water (60-120 ml/L)), Lysol®, and quaternary ammonium compounds like Parvosol®. Thoroughly clean the cat’s living and sleeping areas that were contaminated with stool and if possible, allow to dry for several days before reintroducing cats to those areas. Giardia cysts are quite susceptible to drying. Bathing the dog is also recommended (especially in association with treatment) to wash away cysts on the fur that could get ingested during self-grooming.
ClueJay does not dispense or prescribe medications and there are no FDA-approved medications in the U.S. for Giardia treatment. That said there are two off-label medications (not approved by the Food and Drug Administration (FDA)) for the treatment of Giardia, but are approved for other treatments) medications that are commonly used: metronidazole and fenbendazole. Metronidazole is only available with a veterinarian’s prescription while fenbendazole is also available over-the-counter (OTC). However, because fenbendazole is not approved for this use you won’t find an OTC product with Giardia as a treatment indication. Further, the usual dosing directions on the OTC product probably won’t be effective for Giardia. Unlike some dewormers, neither of these medications are included in monthly heartworm preventatives.
While it is always best to consult with a veterinarian prior to administering any medication, even an OTC version, it’s especially true for off-label treatment of Giardia. There may be patient-specific reasons to choose one medication over another (e.g., underlying health conditions), or reasons to combine them together (or with other drugs like pyrantel) for better safety or effectiveness. Always read the medication administration directions carefully and be on the lookout for potential side effects (like vomiting) when any medication is administered.
Simply put, include a test for Giardia whenever a cat has abnormal stools (soft stool or diarrhea). Even better, include a test for Giardia every time a stool test is done for wellness (once or twice yearly). Need details? Read on.
Veterinarians recommend stool (fecal) testing kittens 2 to 4 times during their first year of life, and 1 to 2 times each year in adult cats (every 6 to 12 months). Veterinarians often call this stool health test a “Fecal O&P”, with the O&P meaning “ova (eggs) and parasites”. It includes special preparations of the stool sample and analysis using a microscope to look for roundworms, hookworms, tapeworms, whipworms, and coccidia. While the Giardia cysts can occasionally be seen using this test type, it is not a reliable method for finding them. The cysts are transparent and very, very small. They are much smaller than worm eggs and even smaller than coccidia spores. Even more challenging, the tiny cysts look different when there is just one versus two trophozoites within the cyst (two “eyes” versus four “eyes”), or if damaged (half-moon appearance). Often Giardia cysts can’t be distinguished from yeast or plant pollen with certainty. Giardia trophozoites (the motile form in the intestines) are even more rare to see with a microscope because they decompose quickly after being passed in the stool. Occasionally if a veterinarian can examine loose, fresh stool right away they can see the trophs before they dissolve. ClueJay Cat Stool Test Level 1 is a stool O&P, so is unlikely to identify Giardia cysts or trophs. However, they will get reported if discovered.
A much more reliable approach is to use a special stool test called “Giardia cyst antigen by ELISA”. An antigen is simply a protein (part of the cyst) which the assay (ELISA) is designed to find. Some veterinarians run the bench-top version of this test at their practice with trained veterinary technicians. Most however, “refer” or ship their patient’s stool samples to an external animal reference laboratory for preparation, analysis, and reporting, where the laboratory technicians and testing processes for Giardia are more specialized. These reference labs typically use microassay wells and high-tech absorbance (wavelength) readers to improve detection success for Giardia. ClueJay Cat Stool Test Level 2 and 3 includes both the stool O&P test and this reference lab version of the Giardia by ELISA test.
Many veterinarians include Giardia by ELISA testing with every stool test done through their practice, whether the stool is normal or abnormal in appearance. This speaks to the commonness of Giardia infections in most areas of the U.S. It also reflects their belief in the importance of knowing if their patients (healthy or not) are infected. This same test is also used to recheck stool samples after treatment. Typically, this “recheck” stool test is done within 2-4 weeks after treating a cat or kitten for Giardia to help confirm that the treatment was effective. If you have other cats in the household, they should be tested as well since Giardia in one cat can often mean Giardia in others.
Another very reliable testing approach for identifying Giardia are Polymerase Chain Reaction (PCR) assays. These tests are designed to find the DNA of Giardia and are done almost exclusively through laboratories that specialize in this type of testing. PCR can detect very small amounts of Giardia DNA present in a cat’s stool sample, from either the Giardia cysts or the trophs. For cats with ongoing intestinal problems, vomiting, soft stools, diarrhea, or weight loss, it’s a good idea to add a Giardia by PCR if the Giardia by ELISA is negative, or just do both simultaneously. ClueJay Cat Stool Test Level 3 includes the stool O&P test, a reference lab Giardia by ELISA, and a specialty lab Giardia by PCR along with PCR for other disease-causing protozoa, bacteria, and viruses found in cat intestines.
With the simple and convenient ClueJay testing solution from home (ClueJay Cat Stool Test Level 2 or 3), you can directly access these professional lab tests for Giardia that many veterinary professionals use every day.
A cat can test positive for Giardia using ClueJay Cat Stool Tests Levels 1, 2, or 3.
ClueJay Cat Stool Test Level 1 is a reference lab stool O&P (fecal ova and parasites) which screens for roundworms, hookworms, tapeworms, whipworms, and coccidia. On rare occasions though, Giardia is “found” under the microscope with this type of test. However, Giardia is much smaller than worm eggs and even smaller than coccidia spores under the microscope, so it’s hard to be certain. It’s best to consider this a “tentative finding of Giardia” or “finding suspicious of Giardia”. When this happens (Giardia suspected from stool O&P), we recommend double-checking with a Giardia by ELISA test through your veterinarian or using ClueJay Cat Stool Test Level 2. A positive ELISA confirms that the initial suspicion was right, and Giardia was present in the stool. If the ELISA comes back negative, then what looked like Giardia (cysts or trophs) wasn’t, and that’s good news. Summary: the stool O&P (Level 1) is a great test to find worms and coccidia, but not Giardia.
ClueJay Cat Stool Test Level 2 adds Giardia by ELISA to the reference lab stool O&P test. This specialized ELISA testing is the standard approach for Giardia testing normal or abnormal appearing stools. It is a much more reliable test for this parasite than the O&P because it uses antibodies (immune proteins) to seek out and attach to any Giardia cyst protein in the sample. A positive test means this Giardia cyst protein was detected in the stool. Most veterinarians then assume the cat is infected with Giardia (called giardiasis) and provide consultation on whether to treat the intestinal infection. A false (wrongly) positive result is possible but rare when using microassay wells and high-tech absorbance (wavelength) readers standard for ClueJay Giardia by ELISA tests. A Giardia by PCR (ClueJay Cat Stool Test Level 3) can be used as a double check for a positive (or negative) Giardia by ELISA result.
ClueJay Cat Stool Test Level 3 adds PCR assay tests (including Giardia by PCR) to the Giardia by ELISA and reference lab stool O&P test. The PCR assay is used to identify Giardia DNA, so it looks for Giardia in a different way than ELISA. Think of it as a very reliable double- check to the ELISA result. A positive PCR test means Giardia DNA (from cyst or troph forms) was detected in the stool. Most veterinarians then assume the cat is infected with Giardia (called giardiasis) and provide consultation on whether to treat the intestinal infection. In most circumstances the results of Giardia by ELISA and Giardia by PCR are identical for the same stool sample (both results negative or both positive). However, on occasion the results don’t match. For a variety of rational reasons, every test can (usually rarely) provide a false (wrongly) positive or false (wrongly) negative result. This is what leads to the development of tests for the same parasite approaching detection differently (such as with Giardia by ELISA and Giardia by PCR).
A Giardia positive result from either ClueJay Cat Stool Test Level 2 (ELISA) or Level 3 (PCR) likely means your cat is infected with Giardia and should be treated; but not always. Healthy cats and kittens with strong immune systems might clear or suppress a Giardia infection on their own, so some veterinarians may hold off treating in certain cases. A test result is not the same as a veterinarian’s diagnosis, so it’s always best to consult with a veterinarian about your cat’s test results to determine the safest and most effective treatment and prevention plan, and when to do follow-up stool tests. Most veterinarians will recommend rechecking a cat’s stool sample within 2-4 weeks after treatment for Giardia. If you have other cats in the household, they should be tested as well since Giardia in one cat can often lead to Giardia in others.
It’s important to know that some cats will continue to test positive for Giardia for an unknown period of time after treatment. This is most likely because the cat remains in an environment where re-infection keeps occurring, but not always. Other considerations for treatment failure are poor immune response, drug resistance, or the trophozoites are in the gallbladder or ducts of the pancreas where the medication is less effective.
A cat can test negative for Giardia using ClueJay Cat Stool Tests Levels 1, 2, or 3.
ClueJay Cat Stool Test Level 1 is a reference lab stool O&P (fecal ova and parasites) which screens for roundworms, hookworms, tapeworms, whipworms, and coccidia. The presence or absence of Giardia cannot be reliably determined with this type of testing. While the stool O&P (Level 1) is an excellent test to detect worms and coccidia, it’s not the right test for Giardia.
ClueJay Cat Stool Test Level 2 adds Giardia by ELISA to the reference lab stool O&P test. This specialized ELISA testing is the standard approach for Giardia testing normal or abnormal appearing stools. It is a much more reliable test for this parasite than the O&P because it uses antibodies (immune proteins) to seek out and attach to any Giardia cyst protein in the sample. A negative test means this Giardia protein was not detected in the stool. Most veterinarians then assume the cat is not infected with Giardia (called giardiasis) and provide consultation on how to prevent an infection in the future. False (wrongly) negative results are possible though. With Giardia this can happen because the Giardia trophozoites in the cat’s intestine were not shedding cysts at the time the stool sample was collected. Without cyst proteins, the test will come up negative even though the cat is infected. For healthy cats with normal stools, additional searching for Giardia isn’t necessary until the next stool test in 6-12 months. However, if your cat has symptoms consistent with giardiasis such as intestinal upset, soft stools, diarrhea, vomiting, or weight loss, then consider re-testing for Giardia but this time by PCR (ClueJay Cat Stool Test Level 3).
ClueJay Cat Stool Test Level 3 adds PCR assay tests (including Giardia by PCR) to the Giardia by ELISA and reference lab stool O&P test. The PCR assay is used to identify Giardia DNA, so it looks for Giardia in a different way than ELISA. Think of it as a very reliable double- check to the ELISA result. A negative test means Giardia DNA (from cysts or trophs) was not detected in the stool. Most veterinarians then assume the cat is not infected with Giardia (called giardiasis) and provide consultation on how to prevent an infection in the future. In most circumstances the results of Giardia by ELISA and Giardia by PCR are identical for the same stool sample (both results negative or both positive). However, on occasion the results don’t match. For a variety of rational reasons, every test can (usually rarely) provide a false (wrongly) positive or false (wrongly) negative result. This is what leads to the development of tests for the same parasite approaching detection differently (such as with Giardia by ELISA and Giardia by PCR). Since cats shed Giardia cysts intermittently, it’s possible to test a stool sample from an infected cat without any cyst protein. In this case the ELISA will be negative (falsely because the cat has the infection). Since trophs don’t normally leave the intestine, a stool without either trophs or cysts could be falsely negative with PCR. That said, a cat with giardiasis is very unlikely to be negative on both ELISA and PCR.
A Giardia negative result from either ClueJay Cat Stool Test Level 2 (ELISA) or Level 3 (PCR) likely means your cat is not infected with Giardia, which is great news. No one wants their cat or kitten shedding Giardia into the home or community environment, putting other cats at risk of infection. Depending on their lifestyle, cats can remain at risk of Giardia exposure so a negative test result today doesn’t mean it couldn’t be positive later. This explains why regularly testing for Giardia (1-2 times per year in adult cats; 3-4 times for kittens) is recommended by many veterinarians along with good hygiene (cleaning up cat stool quickly) throughout the cat’s life. If you have other cats in the household, they should be tested as well since Giardia in one cat can often lead to Giardia in others. Cats negative on both Giardia by ELISA and Giardia by PCR but still with Giardia-like symptoms such as abnormal stools, likely have a different explanation for the symptoms. Please consult with a veterinarian if this is the situation with your cat.
- American Kennel Club, The Facts You Need to Know About Giardia in Dogs
- Pets & Parasites, Cat Owners – Giardia in Cats
- Companion Animal Parasite Center, Giardia
- Merck Veterinary Manual, Overview of Giardiasis
- PetMD, Parasitic Diarrhea (Giardiasis) in Cats
- VCA Hospitals, Giardia in Cats
- Centers for Disease Control and Prevention, Parasites – Giardia
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