Giardia in Cats: A Complete Pet Owner’s Guide to Giardiasis

Giardia is a widespread parasite that can also affect your cat. Learn what it is and its symptoms, as well as what to do if you suspect your cat has giardia.

Giardia trophozoites in microscopic examination. Giardia in cats

Giardia in cats is challenging to completely eradicate since the cysts are extremely likely to reinfect after being shed. Therefore, preventing environmental fecal contamination is essential to preventing reinfection.

Giardia in cats is one of the most widespread parasites in the world. Giardia is infectious to felines, dogs, and humans. It is also infectious to an enormous variety of other animals. This infection has a growing presence in our environment.

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What is Giardia?

Giardia is a parasite that causes a diarrheal disease known as Giardiasis. Giardia can not only affect cats, but also other types of animals and pets such as dogs and even humans. 

This parasitic disease is associated with diarrhea and chronic digestive and metabolic disease.

And so, giardiasis is a microscopic protozoan parasite that causes intestinal infections in both humans and animals. It is also known commonly referred to as G. intestinalis or G. lamblia.

Giardia is a single-celled parasitic species, and contrary to what we’d commonly assume, it is not a worm, bacteria, or virus. It has seven genotypes, with different one’s infecting, humans, dogs, and cats.

Interestingly, the parasite is found all over the world and is a common cause of ‘traveler’s diarrhea’ in humans. And it is also the most common cause of water-borne outbreaks of diarrhea in the United States.

People who drink contaminated water while camping or hiking may get ‘beaver fever,’ which is another name for giardiasis. 

Unfortunately, this parasite has the ability to cause serious illness in cats and other pets if they’re not provided with the right treatment.

How Do Cats Get Infected with Giardia?

Diagrammatic view of the life cycle of giardia in cats. Image showing the transmission of Giardiasis from food and water to humans and animals (cats)
Giardia in the cats’ life cycle and life stages (bottom). Source – CDC 

When a cat consumes the cyst stage of the parasite, it gets infected with Giardia.

The cyst undergoes transformation once it enters the cat’s intestine to become the ‘trophozoite’ or feeding form of the organism. It then clings to the intestinal wall to feed.

If there are sufficient numbers, clinical signs of damage to the intestinal wall will begin to appear.

Trophozoites reproduce by dividing, and some undergo cystic transformation. The cat eventually excretes contagious cysts in its stool.

In dogs, it takes 5 to 12 days for cysts to pass through the feces, while in cats, it takes 5 to 16 days. These cysts can infect another animal immediately.

Giardiasis can be spread by eating or sniffing cysts found in contaminated soil, or by drinking contaminated water.

For Giardia in cats, the contamination usually occurs when they drink water from:

  • Rivers
  • Lakes
  • Puddles
  • Other contaminated water sources.

Cats that live outdoors are, unfortunately, more exposed to the disease. In healthy adult cats, this disease is uncommon. When there are a large number of cysts in the environment due to fecal contamination, the likelihood of developing disease increases.

Cats, especially kittens and elderly cats, are more susceptible to this disease, and it spreads rapidly in overcrowded conditions with groups of cats like a cattery, pet store, or animal shelter.

It has been shown that kittens, in comparison to adult cats, shed more Giardia cysts in their feces.

How Do Indoor Cats Get Giardia?

Unfortunately, protecting your cat from giardia is not all about keeping them indoors. In fact, many indoor cats can get giardia as well. 

The ones at greater risk are those cats from households that also include dogs. This is because a dog can easily bring in giardia when it goes outside.

Cats can also contract giardia from one of their human household members if they’re infected with Giardiasis. This is why it’s essential to follow good hygiene protocols.

The Life Cycle of Giardia

Microscopic view of oval-shaped Giardia cyst.
Source: Wikipedia

Giardia in cats has two main stages in its life cycle:

  • The cyst
  • 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 time. Trophozoites, on the other hand, do not survive in the environment but can cause infections in some cases (fecal-oral contact), too.

Giardia cyst in a microscopic examination. The cyst has an oval shape, and it has a strong outer layer that 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. Giardia in cats
Anatomy of Giardia trophozoite (left) and Giardia cyst (right). Source – Wikipedia.

Giardia in cats occurs 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 exocyst into trophozoites. As opposed to the cystic stage, the trophozoite is mobile. 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.

Types of Giardia Organisms in Cats

There are two types of Giardia organisms. In the intestines of infected animals is a fragile feeding form known as the trophozoite.

Cystic forms, which are shed in feces, are extremely resilient and can survive for months, particularly in damp and watery environments.

As is evident, giardiasis is a common cause of diarrhea in both animals and humans. However, many cats are infected without showing clinical signs, or the diarrhea is misdiagnosed as ‘non-specific.’

Unfortunately, giardiasis in cats is almost certainly underdiagnosed and underreported.

What happens if Giardia in cats goes untreated?

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 leads 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 of Giardia in cats 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 the 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 cystic 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 in cats 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 in cats 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:

What are the Clinical Signs and Symptoms of Giardiasis?

Giardia in cats can be either very simple to diagnose or very difficult, depending on the cat’s age and the health of its immune system.

Giardia in cats’ kittens can have a violent evolution, which makes it easy to notice. Giardia in older cats, on the other hand, can shift into a chronic digestive disease that displays generic symptoms.

This makes it important for pet owners to understand the different clinical signs of giardia in cats to be able to get the right treatment.

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

Diarrhea

Diarrhea is the main symptom of giardia in cats. It is caused by the damage the trophozoites do to the intestinal wall, as well as the improper digestion that occurs as a result.

An acute, sudden onset of foul-smelling diarrhea is brought on by these microscopic parasites attaching themselves to the intestinal wall. It is often pale in color and is poorly formed because food is not digested properly. 

The stool has a very foul smell, it is pale in color and is poorly formed because the food is insufficiently digested. It’s also common to notice excess mucus in the feces of infected cats.

When Giardia in cats occurs for the first time, the diarrhea is acute, but its evolution can be continuous or intermittent.

In older cats, with strong immune systems, 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, diarrhea, associated with malabsorption, can be debilitating.

Digestive Symptoms

Giardia in cats also displays other digestive symptoms, such as:

  • Loss of appetite
  • General apathy
  • Abdominal pain
  • Bloating
  • Vomiting.

The severity of these symptoms differs according to the evolution of the disease.

Weight Loss

As a result of the malabsorption 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 Giardia in cats and the kitty’s immune system.

  • In kittens and cats with poor immune systems and when Giardia also causes severe diarrhea, the weight loss is very easy to notice because they lose a large amount of weight in a short period.
  • 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.

Unfortunately, it’s important to note that it’s also possible for your cat to be infected while showing no signs of illness.

How is Giardia Diagnosed in Cats?

If your cat has diarrhea, you should take him to the vet as soon as you can for treatment since cats can easily get dehydrated if they don’t receive care.

Tell the vet how frequently diarrhea has occurred as well as when the symptoms first appeared. Giardia in cats is characterized by strong-smelling, soft fecal matter. The vet will want to know if your cat’s feces looks and smells like this.

Also, make sure to explain in detail what your cat has been eating to the vet. Changes in nutrition can induce diarrhea in cats, so if you haven’t made any changes, it’s necessary to rule this out as a possible cause.

To obtain an accurate diagnosis, the doctor will most likely need to test your cat’s stool.

How Do You Test for Giardia in Cats?

For an accurate diagnosis, either a fecal smear or fecal flotation test will be done on the sample. If your cat has Giardiasis, the parasite will be present in his fecal matter.

However, it’s not guaranteed that every stool sample will contain the parasite as these tiny giardia cysts tend to shed inconsistently.

Therefore, the vet may need to test multiple samples to confirm it is indeed giardiasis that’s the cause of the symptoms your cat is suffering from. He may ask to test samples from three different days before making an official diagnosis.

Numerous diagnostic comparison studies have been undertaken to determine the best test for detecting Giardia in cats, with one common result — no single test detects all infections.

What is the Treatment for Giardiasis in Cats?

In the United States, no drugs have been approved for the treatment of Giardia in cats.

However, they can be treated with medicine that has been approved for the disease in Europe: a combination of antiparasitic medications. Several types are needed because some are efficient for the cysts, and others for the trophozoites.

Aside from the antiparasitic medication, cats also need the symptoms to be treated, as well. A change in the diet that will help them regain the correct amount of nutrients is required, too.

However, Giardia in cats has been treated safely and with varying degrees of efficacy with:

  • Febantel (which is metabolized to fenbendazole after oral administration)
  • Fenbendazole
  • Metronidazole.

The two medications that are most frequently used to treat Giardia are fenbendazole and metronidazole.

These drugs often come in coated tablet form because they can be quite bitter. The tablet must frequently be split in half, exposing the bitter contents, in order to administer the proper dose to cats.

The bitter taste of these drugs can be masked by having them prepared in flavored formulas by a veterinary compounding pharmacy. The duration of oral administration is usually five to seven days.

Both fenbendazole and metronidazole may be administered individually or in combination.

The combination of the two drugs is typically given to cats with resistant diarrhea that has not responded to treatment. If dehydration or severe diarrhea are present, it may be necessary to administer additional supportive medications.

The best treatment option for your pet can be determined with the help of your veterinarian.

Giardia cysts spread disease as soon as they are released into the environment, so feces should be cleaned up and disposed of quickly. Regular bathing is necessary to remove cysts from the hair coat of infected animals.

Prevalence of Giardia

Giardia in cats has a worldwide distribution and is found in every region of the U.S. The prevalence of Giardia in cats varies greatly depending on:

  • Population, including:
    • Individual pets
    • Group-housed pets
    • Breeding colonies
    • Shelter animals
    • Stray animals
  • Geographic location
  • Diagnostic method used. 

For example:

  • In a survey that used a patient-side antigen test in symptomatic cats from throughout the U.S., 10.8% (512/4977) of cats were positive for Giardia
  • Another survey identified Giardia infection in 31% (36/117) of tested cats from international catteries. 
  • In 2020, the national prevalence of Giardia in cats in the U.S. was 4%. These data were generated by the CAPC from more than 1.8 million feline fecal samples tested for the presence of Giardia by reference laboratories.

But as they do not include cats not taken to the veterinarian or stray cats, and not all veterinary clinics use reference laboratories, 4% can be considered a baseline minimum prevalence is largely asymptomatic individuals.

How to Prevent Giardia in Cats

Bathing is essential for any infected animal in the house to remove fecal debris carrying cysts from the fur.

It’s also a good idea to clean the cattery or home, including the crates, litter boxes, and beds. At the beginning and during the treatment, using a shampoo with chlorhexidine to wash or shampoo the animal, or at least the perianal area, can help get rid of the cysts.

To keep the parasite from spreading, new cats could be tested before they move into a home with other cats. This is possible during the quarantine period.

Zoonotic Implication of Giardia in Cats

Many European studies (in Germany, Italy, Spain, Greece, and Poland) demonstrated the presence of subgroup A in cats, either alone, or as a dual infection. 

Genotype B has also been identified in cats, but A is most prevalent, according to the different European studies and a Canadian one.

The risk of harboring zoonotic Giardia seems to be higher in young cats in less than one year compared to older cats.

A recent study failed to detect zoonotic assemblages in 3 Giardia positive dogs and 2 positive cats living in the Alava region of Spain, suggesting that household transmission of Giardia by pets, if it occurs, is infrequent.

In this study, no simultaneous infections in human and canine/feline hosts by G. duodenalis were demonstrated. Although 29% of dogs and 5.9% of cats tested positive and there was a presence of zoonotic assemblage A was detected in cats in a shelter in the same region.

On the other hand, a study conducted on children from poor environmental conditions in Slovakia showed that cat-specific assemblage F is present in humans in Europe.

To date, there is no study demonstrating direct transmission of Giardia from cats to humans and the main sources of contamination for people appear to be raw vegetables and water.

Moreover, the prevalence of Giardia infection in asymptomatic cats is low in most European countries.

Although there is no proof of direct transmission of Giardia from cats to humans and considering that zoonotic species are sometimes detected in infected (young) cats, the zoonotic potential of Giardia in cats should be considered.

Especially where young cats are living with immunocompromised people. Testing such cats is therefore recommended.

FAQs About Giardia in Cats

Can I get a Giardia infection from my pet?

You can get infected by your cat, but it’s not common. Giardiasis is one of the most common intestinal parasitic infections in cats.

This is because most cats get Giardia from drinking water that is contaminated. And it may be transmitted from cats to humans.

Previously, it was thought that cats and dogs, as well as wildlife, were the primary sources of infection for people.

Genotype A can infect people, dogs, and cats, whereas genotype B can only infect dogs.

But there is also the possibility of human-to-human transmission, and many outbreaks are caused by contaminated water supplies.

How is Giardia in cats spread?

The most common medium of transmission is through contaminated water and food.  
Giardia in cats can be transmitted by:
– Eating or sniffing the cysts from contaminated ground
– By drinking contaminated water. 
Ingestion of food, and soil contaminated with human feces, is a phenomenon particularly common in many developing countries.

How does my cat get infected with Giardia?

A cat becomes infected with Giardia after swallowing the cyst stage of the parasite. This can happen from several causes such as:
– Being in contact with infected feces (poop) from another dog or cat.
– Rolling and playing in contaminated soil.
– Licking its body after contact with a contaminated surface (for example, a dirty litter box, or dog cage or crate).
– Drinking water from a contaminated creek, pond, or other body of water.

Who is at risk of getting infected with Giardia?

According to CDC, those at greater risk are:

– People in childcare settings.
– People who are in close contact with someone who has the disease.
– Travelers within areas that have poor sanitation.
– People who have contact with feces during sexual activity.
– Backpackers or campers who drink untreated water from springs, lakes, or rivers.
– Swimmers who swallow water from swimming pools, hot tubs, fountains, or untreated recreational water from springs, lakes, or rivers.
– People who get their household water from a shallow well.
– People with weakened immune systems.
– People who have contact with infected animals or animal environments contaminated with feces.

How do I protect myself if my cat has a Giardia infection?

Here are a few tips you can follow that will protect you from contracting giardia if your cat currently has it:

1. Wash the cat frequently and keep it isolated until all symptoms have cleared up.
2. Disinfect your home properly with disinfectant.
3. Always wear protective gloves when gardening to reduce the risk of coming in contact with infected poop.
4. Wash your hand properly after using the toilet, after handling cat feces, and before handling, preparing, or serving food.

How long does Giardia survive in the environment?

In the soil

In cold temperatures (around 4ºC/39.2ºF), Giardia can survive for approximately 7 weeks (49 days).

At room temperature (around 25ºC/77ºF), Giardia can survive for approximately 1 week (7 days).

Dry vs. moist surface or environment

In a dry, warm environment that experiences direct sunlight, Giardia can survive for only a few days.
In a moist, cool environment, Giardia can survive for up to several weeks.

Water

In water temperatures below 10ºC/50ºF (for example, lake water or puddle water during the winter, refrigerated water), Giardia can survive for 1–3 months.

In water temperatures above 10ºC/50ºF (for example, river water during the fall, tap water, and puddles during the summer), Giardia can survive for shorter periods of time in colder temperatures.

For example, in water above 37ºC/98.6ºF, Giardia can survive less than 4 days.

How often and for how long should I clean and disinfect after my dog or cat is diagnosed with Giardia?

Clean and disinfect regularly (for as long as your pet is sick) all potentially contaminated items:

– Toys
– Water bowls
– Food bowls
– Pet bedding
– Floors
– Dog crates
– Linens
– Towels
– Litter box
– etc.

If your pet is taking medication, you need to clean and disinfect frequently (daily if possible), until a few days after the last dose of medicine is given.

Giardia’s survival depends on many factors, so we strongly advise that you consult your veterinarian for further advice.

How do I prevent my dog or cat from getting reinfected, or getting my other pets sick, during treatment?

If you have other dogs or cats, make sure you tell your veterinarian, even if they are not showing signs of diarrhea.
Other pets may also be put on medicine depending on the situation.

Even animals showing no signs of Giardia infection could be infected and shedding Giardia into the environment.

Bathe all household pets with pet shampoo, following the medical treatment, to ensure no fecal residue is in the pet’s coat.

Clean dogs’ and cats’ environment (holding areas, floors, crate, etc.) and wash their water bowls daily with soap and water.

Limit your dog’s access to untreated surface water (creeks, ponds, lakes). Do this to avoid re-infecting your animal or contaminating the water, which could make other animals sick.

Best Advice for Giardia from Veterinarians: 

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 @ Safehounds.com

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

Giardia in Ragdoll cat named Jinxy. Cat snuggled between a couch and pillow

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.

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 reacted 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 diarrhea. The metronidazole cleared 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 is good. So I gradually switched him to high-quality canned 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 paste. 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 Chewy.com.

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.

I feel fortunate to be able to work with a veterinarian who is focused on resolving issues and taking the time for that.

Pretty Ragdoll cat with bright eyes sitting on a couch. Giardia in cat
Pretty Ragdoll cat with bright eyes sitting on a couch.

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.


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

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One Comment

  1. 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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