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Giardiasis of cats
Giardiasis is an infection of the intestine by a microscopic parasite, Giardia, invisible to the naked eye. It attaches to the lining of the small intestine and interferes with the absorption of nutrients, resulting in diarrhea that lingers...
What is it?
Giardiasis is an infection of the intestine by a microscopic parasite, Giardia, invisible to the naked eye.
It attaches to the lining of the small intestine and interferes with the absorption of nutrients, resulting in diarrhea that lingers, often oily and smelly.
It mainly affects kittens and cats living in groups. Many adult cats harbor the parasite without becoming ill while spreading it throughout their environment.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Persistent or coming-and-going diarrhea, often pasty, greasy in appearance and with a strong odor.
Possible presence of mucus in the stools.
Bulky stools despite a preserved appetite.
Weight loss or stagnation, particularly visible in kittens.
Dull, pitted coat.
Occasional vomiting.
Dehydration and depression when diarrhea persists in a young animal.
Many adult cats show absolutely no signs.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The parasite exists in two forms: an active form attached to the intestine and a resistance form, the cyst, eliminated in the stools.
These cysts are immediately infective as soon as they are released, which distinguishes giardiasis from intestinal worms whose eggs need time to mature.
They survive for a long time in humid and cool environments, particularly in water and on poorly dried surfaces.
A small amount of swallowed cysts is enough to trigger the infection.
The disease is mainly expressed when the intestinal defenses are fragile: young age, stress, unbalanced diet, presence of other parasites.
Young age: kittens are the most affected and the most symptomatic.
Group living and high density of animals.
Insufficient hygiene of litter boxes, bowls and floors.
Access to stagnant water.
Stress linked to adoption, transport or a change of environment.
Diseases or treatments that weaken the immune system.
Simultaneous presence of other intestinal parasites.
Transmission
By ingestion of cysts present in stools, stagnant water, on the floor, bowls, litter boxes or soiled surfaces.
Through grooming: the cat swallows cysts attached to its coat or that of a friend.
Living in a community strongly encourages the circulation of the parasite: shelters, breeders, colonies, households with several cats.
Wet and poorly dried areas are favored reservoirs.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diarrhea that lasts more than a few days, or any diarrhea in a kitten, warrants a consultation.
Diagnosis is based on stool analysis; as the elimination of cysts is intermittent, sampling over several consecutive days clearly improves reliability.
Rapid detection tests exist and are used in addition by the veterinarian.
A broader assessment is carried out if the general condition is altered, giardiasis can coexist with other causes of diarrhea.
A post-treatment check-up is often offered, especially in the community.
All animals in the household are evaluated, including those without any signs.
Treatment
A specific antiparasitic treatment is prescribed by the veterinarian; Common wormers against roundworms are not all active on Giardia, which explains the failure of random treatments.
Drug treatment alone is never enough: without hygiene measures, the cat immediately reinfests itself from its environment.
The hindquarters coat is cleaned, and clipping this area is sometimes useful in long-haired cats, as cysts cling to it.
Litter boxes, bowls and surfaces are cleaned then carefully dried: complete drying is particularly effective against cysts.
A digestible diet and support for the intestinal flora often accompany treatment.
Rehydration is necessary when diarrhea has weakened a kitten.
All animals in the household are treated at the same time when the veterinarian deems it necessary.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Clean the litter box daily and disinfect it regularly, allowing it to dry completely.
Wash the bowls every day and change the water frequently.
Avoid access to stagnant water.
Pick up stools without delay, as cysts are infesting as soon as they are emitted.
Limit overpopulation and respect the number of litter boxes appropriate to the number of cats.
Isolate and examine any new arrival before integrating them into the group.
Wash your hands after cleaning the litter box, and make sure children do it too.
Keep other pest control treatments up to date.
Possible complications
Dehydration, particularly in kittens, may require hospitalization.
Growth retardation and weight loss during prolonged infections.
Chronic diarrhea difficult to control until the environment is cleaned up.
Repeated reinfestations in communities, discouraging if hygiene measures are not applied everywhere.
Worsened when other parasites or intestinal disease coexist.
When to see a veterinarian
Your cat's diarrhea lasts more than two to three days or returns regularly.
Your kitten has diarrhea: consult quickly, dehydration occurs quickly.
The stools are oily, smelly, or contain mucus.
Your cat is losing weight or is not growing normally despite having a good appetite.
He is depressed, refuses to drink or appears dehydrated.
The diarrhea persists despite deworming given at home.
Several cats in the household have loose stools at the same time.
Transmission to humans
Giardia is considered potentially transmissible to humans, but most forms found in cats are adapted to this species and the risk to humans is considered low.
Human contamination would occur by ingestion of cysts present on soiled hands or surfaces, never by a simple caress; in humans, contaminated drinking water remains the most common source.
Fragile people, young children and people whose immunity is reduced, must be more attentive to hygiene measures.
Protective actions are simple: wash your hands after cleaning the litter box and before meals, pick up stools without delay, clean and dry surfaces carefully, do not let children handle the litter box.
In the event of digestive problems in a person in the household, a doctor should be consulted, reporting the presence of animals.
Prognosis
The prognosis is good in healthy adult cats, with diarrhea generally resolving with appropriate treatment.
In kittens treated quickly, growth returns normally.
Difficulties almost always come from reinfestation from a poorly sanitized environment, particularly in a community: this is where long-term success comes into play.
Frequently asked questions
My cat does not have diarrhea but his test is positive, should he be treated?
Not systematically. The veterinarian decides according to the context: presence of young animals, fragile people in the home, community life. A carrier without signs can nevertheless contaminate their environment.
Is a classic dewormer enough?
No. Giardia is not a worm and not all dewormers eliminate it. The appropriate product is prescribed after diagnosis.
Why does diarrhea come back after treatment?
Most often because the cat reinfests itself from litter, bowls or its own coat. Cleaning, thoroughly drying surfaces and caring for the coat are as important as medication.
Can I get giardiasis from my cat?
The risk is considered low, with feline forms being largely specific to cats. Washing your hands after cleaning the litter box remains a common sense precaution, especially with young children.
References
ESCCAP — European Scientific Counsel Companion Animal Parasites
CDC — Centers for Disease Control and Prevention
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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