Tritrichomonas Foetus Infection in Cats

Michael Kearley, DVM
By Michael Kearley, DVM on Jun. 1, 2023

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What Is Tritrichomonas Foetus Infection in Cats?

Tritrichomonas foetus, or T. foetus, is a common parasite that causes chronic feline large bowel diarrhea, often seen in young cats and kittens. T. foetus is especially suspected when symptoms reoccur after typical treatments of most diarrhea causes have been used.

Fortunately, this infection and the chronic diarrhea it causes is often considered more of an inconvenience than a medical emergency. However, because diarrhea has multiple causes and can lead to significant metabolic problems and dehydration, it shouldn’t be ignored. Seek help from your veterinarian promptly if your kitty has diarrhea that persists longer than a few days and has accompanying symptoms (listed below).

Symptoms of Tritrichomonas Foetus Infection

Some cats may not show any symptoms associated with T. foetus infection, especially those that are older and in otherwise good health. For most cats, though, the typical symptom is diarrhea that has an extremely bad odor and often contains mucus and/or bright red blood. Cats with T. foetus infection typically have a normal appetite and do not vomit or experience weight loss. But they can experience:

  • Flatulence

  • Straining to defecate

  • Fecal dribbling/incontinence

  • Inflammation of the anus

  • Increased urge and frequency of defecation

  • Variety of colored stool, though mostly normal

Causes of Tritrichomonas Foetus Infection

T. foetus is a single-celled, pear-shaped protozoan flagellated organism that takes over the cat’s small intestine and colon. Its life cycle consists of only one stage, termed a trophozoite, and once in the gastrointestinal (GI) tract, this reproduces and is then shed in the feces for other cats to ingest, often attributed to grooming—where it can spread to other cats.

Tritrichomonas foetus infection has been found worldwide and in greater occurrences in multi-cat residences such as catteries and shelters. Though all cats are susceptible, young cats and kittens are more susceptible to infection in general, and purebred cats have a higher incidence of infection, probably in association with breeding facilities.

How Veterinarians Diagnose Tritrichomonas Foetus Infection

There are three routes of testing a veterinarian may recommend to diagnose your cat with T. foetus. Fresh fecal samples without litter contaminant are needed. Tests will include:

  • Fecal culture: This test can be performed either in the clinic or at a reference laboratory and often increases the likelihood of detecting the organisms.

    • In some circumstances, a saline flush procedure may be conducted, where a catheter is inserted into the cat’s anus (this often requires sedation), the colon is flushed with saline, and fecal matter is aspirated.
  • PCR: This is the most sensitive test and requires a reference laboratory. It looks for trace DNA of the organism in your cat’s stool. 

  • Fecal smear: Often performed in the clinic, this is a microscopic examination of your cat’s fresh feces.

Bloodwork, routine stool exams (often to rule out other parasitic causes), and imaging such as radiographs or ultrasound may be recommended.

Treatment of Tritrichomonas Foetus Infection

Often, many approaches for treating chronic diarrhea have been tried unsuccessfully before a true diagnosis of T. foetus is confirmed.  

Examples of such treatments include dietary management with a high-fiber diet or a “gastrointestinal-friendly” diet aimed at improving fecal consistency or reducing inflammation in the gut; prebiotics, probiotics, or a combination of both to help promote growth of beneficial bacteria, decrease inflammation, and aid with immune system functions; anti-diarrheal medications; and antibiotics and/or medications such as metronidazole or fenbendazole

Even when diagnosed, these treatments are often unsuccessful, or they may be successful at first only for symptoms to reoccur once medications are finished or the cat’s diet is changed.

Other medications such as tinidazole or ronidazole have been shown to be effective at treating T. foetus infections. Ronidazole is the medication of choice, but it must be used with caution. It should only be used in confirmed cases and by prescription from a licensed veterinarian. Talk to your vet about the risks and benefits of such medication if your cat or kitten has a T. foetus infection.  

Recovery and Management of Tritrichomonas Foetus Infection

For some cats with only mild or intermittent symptoms, or if treatment is not an option due to treatment side effects, cost, or pet parent preference, it should be noted that diarrhea due to T. foetus can resolve on its own, although it could take at least two years and the cats will remain carriers of the parasite for life.

For many cats who receive treatment, the long-term prognosis is good. The duration of the treatment is usually about two weeks, with most cats showing improvement with fecal consistency in just a few days. Diarrhea may persist for a short while after treatment as the secondary inflammation resolves.

Persistent infection can occur in about 25% of cats despite treatment, and these cats may require additional treatment of either a higher dose of medication or for a longer period of time.

Fortunately, the organism doesn’t survive very long in the environment and is easily killed by most routine disinfectants. Measures such as good litter box hygiene (scooping and cleaning daily), isolating infected cats especially during treatment, minimizing stress, and avoiding crowded living conditions are recommended. Screening of all cats in breeding facilities or shelters, when applicable, is also advised. 

Tritrichomonas Foetus Infection FAQs

How do cats get Tritrichomonas foetus infection?

T. foetus is transmitted through the fecal-oral route, meaning for a cat to become infected, it must ingest the organism, which is shed in the feces. Litter box sharing is by far the most common mode of transmission. Indirectly, contaminated food and water bowls and ingestion of certain slugs may also be routes of transmission.

Is tritrichomonas foetus contagious to other cats?

Yes. T. foetus is often passed on to other cats through shared litter boxes, as cats often ingest the organism due to their grooming habits.

Can Tritrichomonas foetus be spread from cats to humans?

Fortunately, no. T. foetus has not been shown to be zoonotic (transmissible from animals to humans). Still, good hygiene and hand washing techniques are advised, and people with a weak immune system generally should refrain from changing the litter box and handling feces. Always consult your doctor with any questions regarding personalized medical advice.

Featured Image:


Yao C, Köster LS. Tritrichomonas foetus infection, a cause of chronic diarrhea in the domestic cat. Veterinary Research. 2015;46(1).

‌Collántes-Fernández E, Fort MC, Ortega-Mora LM, Schares G. Trichomonas. Parasitic Protozoa of Farm Animals and Pets. Published online November 8, 2017:313-388.


Michael Kearley, DVM


Michael Kearley, DVM


Dr. Michael Kearley graduated from the University of Florida College of Veterinary Medicine in 2013. He graduated with a certificate in...

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