Overview of T. foetus in Cats

Tritrichomonas foetus (T.Foetus) is a protozoan parasite that infects pigs, cows, birds, and cats all over the world. Although a single name refers to the species infecting all animals, at the time of writing scientists are in the process of identifying and differentiating Tritrichomonas blagburni, which affects cats, from Tritrichomonas foetus, which affects cattle. T. foetus lives in the intestinal tract of animals and infection is either asymptomatic or results in gastrointestinal symptoms. It is considered one of the most infectious causes of large bowel diarrhea in cats.

Commonly referred to by vets as “tri-trick, ” T. foetus infections show no gender or breed predilection but are most common in young cats and in cats under close confinement such as those in kennels, animal shelters, catteries, hoarding homes, and pet stores. The first case of T. foetus was recorded in 1996 and the parasite can infect cats from 1 month to 16 years of age.

T. foetus lives in warm, moist cavities and thrives in the distal small intestine (ileum) and colon of cats where it causes chronic diarrhea. It is believed that cats can become symptomatic months to years after exposure.

Transmission of T. foetus is by fecal or oral route, and it can live for several days in wet stool. The predominant transmission theory proposes that during litter box usage, a cat can get stool on his paws from an infected cat which is later ingested while grooming. There is no evidence of sexual transmission.

If left untreated, research has suggested that diarrhea may resolve within 2 years but the subject can continue to carry the infection for the rest of their life.

T. foetus can be transmitted to humans in very rare cases. Only one report has been documented in an individual who was severely immunocompromised.

What to Watch For

• Diarrhea may contain mucous and/or blood
• Classic diarrhea is “cow-pie” consistency
• Most cats maintain good body condition and good overall health
• Some cats have a very strong and unpleasant odor to their stool

Diagnosis of Tritrichomonas foetus Infection in Cats

Veterinary care should include diagnostic tests and subsequent recommendations.

Diagnostic tests are needed to recognize T. foetus and exclude other diseases. A test for T. foetus is not a part of routine testing in cats.

Tests may include:

• Direct fecal smears used to look for a stage of the organism called “trophozoites.” A positive direct smear suggests the diagnosis of T. foetus; however, the organism can appear mistaken for a similar organism called Giardia . The treatment for these two organisms is different. Note that this test may only identify 14% of infected cats and an infected cat may still test negative.
• A fresh fecal sample, essential for diagnosis. These can be obtained by collecting a freshly voided sample free of litter or by obtaining a fresh sample with a fecal loop. A colon flush is often required to obtain feces high in the colon where T. foetus congregate. This consists of inserting a small red rubber catheter in to the rectum, flushing in sterile saline and pulling back some of this fluid which is then tested for presence of T. foetus .
• Fecal culture of T. foetus , facilitated by specific culture medium that fosters its growth. A fecal culture can identify infection in up to 55% of cats.
• The Polymerase Chain Reaction (PCR) test, which identifies T. foetus DNA extracted from the fecal sample.
• An enzyme-linked immunosorbent assay (ELISA) test to identify Giardia antigens in the stool, which may be important to rule out concurrent disease. Diagnosis of T. foetus should be considered in any cat that was previously diagnosed with Giardia and fails to respond to treatment.
• Colonic mucosal biopsy to identify parasites in the lining of the colon.
• It is notable that Tritrichomonas foetus cannot be detected by routine fecal float tests as the parasite is routinely killed by refrigeration.

Treatment of Tritrichomonas foetus Infection in Cats

Treatment for pets with T. foetus infection includes treatment with ronidazole. This is the only drug that has been effectively demonstrated to eliminate T. foetus.

There is a narrow margin of safety with this drug; the dose which effectively kills T. foetus is close to the toxic dose. A typical dose is approximately 30 mg/kg once daily for a maximum of 14 days. As a result, very careful observation of side effects is required.

Common side effects of ronidazole in cats include lethargy, lack of appetite, loss of balance and coordination (ataxia), and seizures. Most side effects are associated with higher doses. Cats that develop signs of toxicity will generally return to normal within a week to a month after discontinuation of therapy.

Prevention of ronidazole toxicity includes using the 30 mg/kg dose and monitoring closely for signs of toxicity. Any signs of lethargy and lack of appetite should warrant an immediate call to your veterinarian who will likely discontinue treatment.

Ronidazole should not be used in pregnant cats, nursing kittens and cats, and cats less than 8 weeks of age.

Most cats will return to normal within 8 days to a month following initiation of treatment.