Parasitic Diarrhea (Giardiasis) in Cats

Published on
Last updated on
6 min read

Key takeaways

Giardiasis refers to a parasitic infection by one of several protozoans in the Giaridia family. In many cases this microorganism lives in infected cats without causing any harm or symptoms.

  • In some cases, particularly in cats with compromised immune systems, cats who live in crowded circumstances, or young cats, giardiasis becomes symptomatic, causing diarrhea and abdominal discomfort
  • With severe, long term infections, weight loss, dehydration, loss of appetite and lethargy may occur
  • Veterinary attention is required in cases where symptoms develop
  • Diagnosis is based on physical examination and fecal analysis
  • Treatment includes deworming medications, antibiotics, anti-diarrheals, microbiome restorative therapy and diet therapy
  • During treatment, bathing of the patient is required and careful hygiene practices must be observed
  • Prognosis with treatment is typically good
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A closer look: Parasitic Diarrhea (Giardiasis) in Cats

There are several species of protozoa in the Giaridia family which are intestinal parasites capable of infecting cats.

The severity of giardiasis depends on how severe symptoms are and how long they last. Cats with mild giardiasis experience a few episodes of diarrhea with a small volume of feces. Cats with severe giardiasis experience many episodes of diarrhea with larger volumes of feces. In rare cases, giardiasis continues long term, or is intermittent but long standing. In these cases, weight loss, decreased appetite, and lethargy may occur. Significant weight loss is sometimes fatal in cats.

It is not entirely clear why some cats develop symptoms while others carry the infection without any signs. Additionally, cats who have no symptoms can transmit the infection, making potential sources of transmission very difficult to predict.

It is possible for some types of Giarida to transmit from cats to humans. Humans who are in contact with infected cats or their fecal matter must wash their hands after contact. When transmission between cat and person occurs, the immune system of most humans prevents symptoms from developing. People with compromised immune systems are more susceptible to giardiasis. If symptoms develop, medical attention is required.

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Risk factors

Giardiasis occurs in a significant proportion of the cat population without any symptoms or harm. Cats that develop symptoms require veterinary attention.

Some cats are more susceptible to symptomatic giardiasis including:

  • Young kittens
  • Cats with compromised immune systems due to illnesses such as FIV and FeLV
  • Cats on immune suppressing medications
  • Cats who live in crowded circumstances such as in breeding operations, boarding facilities, shelters, or feral cat colonies

Possible causes

Giardiasis is an intestinal parasitic protozoan infection by one of microorganisms in the Giardia family. The life cycle of Giardia has two stages: the cyst and the trophozoite.

Giardia is only transmissible in its cyst form. This form is excreted with the fecal matter of an infected animal and passes to a healthy animal when it eats or drinks contaminated food or water, or comes in contact with an infected animal or contaminated surface. As a cyst, Giardia is very hearty, surviving in moist, dark environments for weeks or months.

Once it has been ingested, the cyst form sheds its tough exterior, turning into the trophozoite form. This form attaches to the wall of the intestine, sometimes causing symptoms.

Main symptoms

In cases of giardiasis, diarrhea is usually described as:

  • Poorly formed
  • Pale
  • Malodorous

Testing and diagnosis

Cats with the symptoms of giardiasis require veterinary attention.

Diagnostic tools include:

  • Physical examination
  • Fecal analysis
  • ELISA test: a specialized bloodtest

Fecal analysis must be repeated if no evidence of the organism is found and symptoms persist, as false negatives are possible due to the nature of the parasite's life cycle.

Steps to Recovery

Treatments include:

  • Deworming medications
  • Antibiotics
  • Supportive care
  • Microbiome restorative therapy (fecal transplant)

Follow up testing is required to confirm that the infection has been controlled.

The prognosis for cats with symptomatic giardiasis that receive treatment is good. Cats that do not receive treatment, particularly cats who have long-term or intermittent giardiasis and therefore lose significant weight, have a more guarded prognosis.


There are no proven preventative measures to avoid giardiasis infection. Reinfection, or transmission to other cats in a group when a confirmed infection is present in the group can be prevented.

With known infection, bathing with shampoo is recommended in order to rid the fur of fecal matter and parasites to prevent reinfection or transmission to other cats. Once treatment is complete, another bath is necessary.

Litter trays must be emptied daily and fecal matter disposed of carefully during treatment.

Surfaces must be disinfected. Possible methods of disinfection include:

  • Freezing
  • Direct sunlight
  • Chemical disinfectant, especially quaternary ammonia

Prior to disinfection, thorough cleaning to remove all fecal particles is necessary where possible.

Avoiding surfaces that can not be cleaned (soil, grass, etc) is recommended where possible during treatment.

Humans that handle infected cats or their litter trays must wash their hands in order to avoid recontamination of their pet.

Is Parasitic Diarrhea (Giardiasis) in Cats common?

Infection with Giardia is common. Infection cats do not always develop symptoms or illness.

Typical Treatment

  • Anitparasitics
  • Antibiotics
  • Bathing
  • Increased hygiene protocols
  • Supportive care
  • Anti-diarrheals
  • Dietary therapy
  • Microbiome restorative therapy (fecal transplant)
  • Fluid therapy


No Author - Writing for Companion Animal Parasite Council
Lucy J. Robertson - Writing for Merck Veterinary Manual
Sharon Patton , Peter D. Constable - Writing for Merck Veterinary Manual
No Author - Writing for Veterinary Partner
Matt Brewer - Writing for Today's Veterinary Practice

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