Giardia in Cats

Last Updated on July 8, 2021 by Jenny

Giardia in Cats – Here is Why It Is Especially Dangerous

Giardia is one of the most widespread parasites in the world. It is infectious to cats, dogs, and humans, but also to an enormous variety of other animals, which increases its presence in the environment enormously. This parasitic disease is associated with diarrhea and chronic digestive and metabolic disease. In this article, we are going to outline the most important details about this parasite, its life cycle, its transmission, as well as the main symptoms of giardiasis, and what you should do if your cat should become infected.

Adult Cat after Giardia
This is Jinxy who had Giardia as a kitten. Jinxy’s mom wrote about his story below.

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The Highlights: 

  • Giardia in cats or giardiasis is a disease caused by parasites.
  • It is contagious and needs to be treated by a veterinarian 
  • Symptoms of Giardia are diarrhea, weight loss and digestive symptoms 
  • Hygiene is the most important preventative measure to control Giardia infections in cats and spread in the household. 
  • Recommended product for keeping the litter box as clean as possible is the Litter Robot

What Is Giardiasis?

Giardiasis is the diarrheal disease caused by the Giardia parasite. This parasitic disease commonly occurs in cats, dogs, and people, as well as many other mammals, both wild and domestic, but also birds. There are several species of Giardia, but the most important is G. intestinalis, also known as G. lamblia and G. duodenalis, which can infect cats, dogs, and people. Cats may also be infected by G. felis. However, cross-infections can also occur.

What Is Giardia?

Giardia intestinalis (also known as G.lamblia or G. duodenalis) is a water-borne parasite that can infect all mammals. Giardiasis can be transmitted from humans to animals, and from animals to humans (zoonosis) because the same pathogen is infectious to both humans and animals. It is a flagellated (has a flagellum that enables it to move) single-celled microorganism that commonly causes diarrheal disease all over the world and it is the most common cause of waterborne outbreaks of diarrhea in the United States.

Collage of cats with text \"Giardia in cats - here is why it is especially dangerous\"

How Does Infection with Giardia Occur?

Infection occurs when the host (cat, human, or other mammals) ingests Giardia cysts with contaminated water or, less commonly, with contaminated food or via direct fecal-oral contact (unwashed hands). In cats, the contamination usually occurs when they drink water from rivers, lakes, puddles, or from contaminated sources. 

Outdoor cats are exponentially more exposed to the disease, but also indoor cats from households that also include dogs because the dog can get infected when it goes outside. If one of the human members of the household becomes infected with Giardiasis, he or she could transmit the disease to the cat as well unless solid hygiene protocols are instated.

Life Cycle of Cyst

Giardia life cycle and life stages (bottom) – Source – CDC 

The Life Cycle of Giardia

Giardia has two main stages in its life cycle – the cyst and the trophozoite. While both of these are passed in the infected host’s feces, the cysts are the most infectious because they can survive in the environment for a long period of time. Trophozoites, on the other hand, do not survive in the environment but can cause infections in some cases (fecal-oral contact).

Giardia cyst in microscopic examination

Giardia cyst in microscopic examination – Source – Wikipedia

The cyst has an oval shape and it has a strong outer layer which is adapted to protect it from the harmful effects of the environment. The main role of the cyst is to help the parasite located inside it to survive outside of its host. Cysts are not mobile, so they will remain in the area where the infected host has excreted them, waiting for a new host to come and pick them up.

Anatomy of Giardia trophozoite and Giardia cyst

Anatomy of Giardia trophozoite (left) and Giardia cyst (right) Source – Wikipedia

When the cat ingests the cysts, these pass through the digestive tract. When they are exposed to the highly acidic environment in the stomach, the outer layer which had protected them outside of their host finally breaks down, unleashing the parasite into the host’s digestive tract. When the cysts reach the first portion of the small intestine, the duodenum, they excyst into trophozoites. As opposed to the cystic stage, the trophozoite is mobile because it has 4 pairs of flagella that enable it to move in the intestine. When they reach the brush border of the intestinal wall, they adhere to it using a sucking disk.

Giardia trophozoites in microscopic examination

Giardia trophozoites as seen in microscopic examination – Source – Wikipedia

When the trophozoites feed, they adhere closely to the villi on the brush border and suck in the nutrients, damaging the intestinal wall in the process. Considering that the host usually ingests a large amount of cysts, which excyst into trophozoites, and which reproduce rapidly, the number of trophozoites feeding on the small intestine is enormous, making the damage to the intestinal wall important.

These lesions to the intestinal wall affect the absorption process, which leads to malabsorption in the host (the incomplete absorption of nutrients). The inflammation in the intestine and the improper digestion lead to diarrhea, which has a particularly foul smell because the food has not been fully processed in the digestive tract. This is also the reason why cats suffering from giardiasis lose weight rapidly.

The trophozoites feed on the nutrients they extract from the intestinal wall to gather the resources they need to multiply. Multiplication in Giardia occurs by binary fission, which means that one trophozoite can essentially duplicate itself. This also happens in the duodenum, the first portion of the small intestine (this is why the species is known as G.  duodenalis). Then, as they pass in the jejunum, the second portion of the small intestine, they come in contact with biliary fluid.

The parasite then senses that the surrounding environment is not suitable for it anymore, so it switches back to its survival stage, the cyst. However, only some of the trophozoites form cysts. From the jejunum on, the parasite (both in trophozoite and cystis form) passes through the intestinal tract until it is excreted with the feces into the environment. The trophozoites die quickly outside of the host, but the cyst can resist for a long time, waiting for a new host. Thus, the life cycle of the Giardia parasite is complete.

Epidemiology – This intestinal parasite is distributed globally and it occurs in both developed and developing countries.

Reservoir – The main reservoir for humans are other humans infected with the parasite. Giardia is also particularly prevalent in cattle, especially in calves, which eliminate a large number of infectious cysts in the environment, which contaminate the waters in the region. People who live close to cattle farms should be aware of this and avoid using water from ponds and lakes. They should also wash their hands regularly and avoid touching their mouths with unwashed hands.

Symptoms of Giardiasis in Cats

Giardiasis can be either very simple to diagnose or very difficult, depending on the cat’s age and the health of its immune system. In kittens, giardiasis can have a violent evolution, which makes it easy to notice. In older cats, on the other hand, it can shift into a chronic digestive disease that displays generic symptoms.

Recognizing the Infection with the Giardia parasite

Here are the main symptoms that occur when cats become infected with G. intestinalis:


This is the main symptom of this parasitic infection. It is caused by the damage that the trophozoites do to the intestinal wall, as well as the improper digestion that occurs as a result. The stool has a very foul smell, it is pale in color and is poorly formed because the food is insufficiently digested, which is actually visible – it is mucous, with noticeable fatty portions. In kittens and cats that come into contact with Giardia for the first time, the diarrhea is acute, but its evolution can be continuous or intermittent. In older cats, with strong immune systems, the diarrhea can be limited to a softening of the stool, which is usually not noticed. In cats with poor immune systems, on the other hand, the diarrhea, associated with the malabsorption, can be debilitating.

Digestive Symptoms

Aside from the diarrhea, cats infected with Giardia also display other digestive symptoms, such as loss of appetite, general apathy, abdominal pain, bloating, or even vomiting. The severity of these symptoms differs according to the evolution of the disease.

Weight Loss

As a result of the malabsorbtion caused by the presence of the parasite in the intestine, cats infected with Giardia do not absorb the right amount of nutrients, even though they are fed the right amount of food. This leads to weight loss, which varies in severity according to the evolution of the Giardiasis and the cat’s immune system. In kittens and cats with poor immune systems, in which the Giardiasis also causes severe diarrhea, the weight loss is very easy to notice because they lose a large amount of weight in a short period of time. In older cats with strong immune systems, on the other hand, the weight loss may not be so easy to notice because it happens over a longer period of time.


In the United States, no drugs have been approved for the treatment of giardiasis in cats. However, they can be treated with medicine that has been approved for the disease in Europe – a combination of antiparasitic medication. Several types are needed because some are efficient for the cysts and others for the trophozoites. Aside from the antiparasitc medication, cats also need medication to treat the symptoms, as well as a change in diet that will help them regain the correct amount of nutrients.

Best Advice for Giarida from Veterinarians: 

Best Advice for Giarida

Hygiene is the most important preventative measure to control Giardia infections in cats and spread in the household.  Do not allow your cat to drink from contaminated water sources or eat contaminated food.  Bathe infected animals to remove feces that may contain cysts from their fur coat.  Also, make sure to wear gloves and wash your hands when cleaning and dealing with feces. 

Dr. Michelle Burch, DVM @

Will Giardia go away on its own in cats?
Giardia will usually not go away on its own and many cats need to be on prescription medication to treat it.
How contagious is Giardia in cats?
Giardia is very contagious in cats. It is not uncommon to have outbreaks of it if many cats live in the same home or environment.
Will vinegar kill giardia?
No, vinegar will not kill giardia. Treating giardia requires a course of an antibiotic, called metronidazole, and sometimes also requires fenbendazole, a dewormer.
How do I disinfect my house from Giardia?
Disinfect with diluted bleach- the litter box and areas the cat frequents. Clean the litter box frequently to prevent reinfection. Dr. Leslie Brooks, DVM, MPH Verternary Advisor @ Betterpet
Recommendation for keeping the litter box area clean:

Litter Robot and a full review after 5 years

Giardia in Cats – A Reader’s Experience

Jinxy and Giardia – written by Jinxy’s mom, Judy.

My kitten, Jinxy was born June 11, 2018 and I picked him up when he was approximately 3 months old. He was a wonderful kitten, extremely loving and playful but immediately started to have consistent diarrhea, sneezing, and eye discharge. I initially took him to my veterinarian for a wellness check and testing just to ensure everything was okay. It was quickly determined that he had several issues including calicivirus and mycoplasma. My breeder was excellent in helping me to ensure Jinxy was getting proper treatments and also covered the cost of my vet visits. She suggested giving him plain Greek yogurt and pumpkin to help with the diarrhea issue.
Jinxy as a sick kitten with Giardia
After a few weeks and after taking all of his medications, Jinxy was still experiencing diarrhea so the breeder offered to take him back to her veterinarian to have him checked there. She was concerned because Jinxy has received the calicivirus vaccine and thought he possibly had a reaction to it. At that time her veterinarian discovered he had hookworms which he was immediately treated for. The breeder kept Jinxy for one month to ensure he was diarrhea-free and gave me frequent updates on my kitten’s health which was comforting.
Once we got Jinxy back home, he was fine for a day or two but then diarrhea returned. At that point, I took him back to my veterinarian who did a thorough exam including bloodwork and an extensive intestinal parasite lab test that a normal fecal exam and lab did not include. Several days later we received the lab results confirming our boy had giardia. 
Jinxy’s giardia was treated with metronidazole. He was on this medication for 2 weeks and his persistent diarrhea was eliminated as was the giardia after that. It never returned and neither did the  diarrhea. The metronidazole cleared the diarrhea up within 2 days.
During the time of Jinxy’s giardia treatment, I did extensive research on cat foods and slowly began changing his diet. He had been eating Science Diet dry kitten food and Royal Canin can kitten food. Through research, I discovered neither are good. So I gradually switched him to a high quality can food and a variety of freeze-dried raw foods. Currently, at 2 1/2 years old he is eating Dr Elsey’s Clean Protein can food mixed with Stella & Chewy’s freeze-dried raw chicken, duck, rabbit and Primal freeze dried raw turkey. I add quite a bit of water to this mixture to form a wet pate. He also gets about a tablespoon of Vital Essentials freeze-dried raw mini nibs in the chicken and turkey for a bit of crunchy food. Jinxy eats twice daily. I add Dr Mercola Complete Probiotics to the wet food each time and I also add in 1/2 teaspoon of The Missing Link feline formula. He gets one spirulina tablet daily made by Dr Mercola. I order everything from
The combination of his giardia medication and the food switch completely cured my boy. He has not had one bout of diarrhea in 2 years and has one bowel movement daily that is almost odorless. I have never had to clean his bottom. I believe the food change worked miracles. Jinxy is extremely healthy with great kidney numbers so I’m confident the giardia had no long-lasting effects.
Healthy grown cat after giardia treatment
I feel fortunate to be able to work with a veterinarian who is focused on resolving issues and taking the time for that. When I learned Jinxy had giardia I was worried because I thought it would be difficult to resolve. But with persistence in ensuring he had his litter box cleared 4-5 times daily, making certain he took all medications as directed, and changing his diet, I am fortunate to now have a very healthy cat with no gastric or respiratory issues. 
Jinxy is currently recovering from a broken hind leg and femoral head removal surgery. That’s a story for another time. Sometimes I think there may be truth in a name. 




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One thought on “Giardia in Cats

  1. Patti Johnson says:

    HAPPY NEW YEAR’S EVE! TYSVM for such a SUPER PAWESOME & FABULOUS POST, Jenny honey! What a horrible illness! Yikes! So glad Jinx recovered! A BIG TYSVM to Jinx’ mom, Judy, for sharing! <3

    Big hugs & lots of love & purrs & HAPPY NEW YEAR!!!

    Patti & Miss Pink Sugarbelle 🙂 <3 <3 <3

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