There are numerous parasites and pathogenic organisms that can infect cats. Tritrichomonas foetus, while traditionally recognized as a parasite that causes reproductive harm in cattle, has been added to the list of potential causes of diarrhea in our feline companions. Cats kept in groups, such as in breeding catteries and shelters, are especially susceptible to Tritrichomonas. The parasite is spread through a fecal to oral transmission route, so cats who share litter boxes can pick up the organisms on their feet and ingest them while grooming. It can remain viable and infectious for up to three days in fecal material, and it is resistant to drugs typically used to treat diarrhea caused by similar organisms.
Tritrichomonas foetus is microscopic; thus, it will not be visible in the stools of infected cats to the unaided eye. It is a flagellated protozoan, a single-celled organism that is able to propel itself by the use of whip-like appendages called flagella. These organisms may be mistaken under the microscope for Giardia, a similar parasite common in pets. When misidentified and treated with traditional anti-protozoan drugs, the diarrhea caused by the parasite will persist or only temporarily improve.
The symptoms associated with Tritrichomonas typically occur within days of infection; however, some cats may be silent carriers of the parasite, exhibiting no symptoms at all. They can be reservoirs of infection for subsequently exposed cats. Large bowel colitis, characterized by bloody diarrhea with mucous, is the typical presenting symptom. Affected cats are usually generally healthy, alert and active, with the only signs of illness being the presence of anal redness or swelling, and painful defecation. Involuntary dribbling of feces may be present. Vomiting does not usually accompany T. foetus infections.
Tritrichomonas is suspected in any case of feline diarrhea that is refractory to treatment. There are several methods of testing for the parasite available to the veterinarian. It is important to screen all cats with diarrhea for Tritrichomonas if T. foetus is initially suspected. Screening involves testing a fresh stool sample for visual confirmation of the motile flagellates under the microscope. This test is called a direct smear, and must be performed in-house, because the protozoa will quickly desiccate and become unidentifiable at the reference laboratory. The parasite may be missed altogether if the fecal sample is too dilute or if there are very low numbers of the organisms.
The stool can also be cultured for Tritrichomonas. A specially designed culture bag called the InPouchTF can be used to grow and increase the numbers of the parasites until they can be identified under the microscope.
There is also a DNA test available to confirm the presence of Tritrichomonas in feces. This is called a PCR test or Polymerase Chain Reaction test. While it is the most sensitive test available, it is also relatively expensive and requires a larger amount of fresh stool to analyze. It is not widely available and must be run at a specially equipped reference lab. The PCR test is usually reserved for patients that are highly suspected of T. foetus infection, but all other testing has been inconclusive.
The treatment for Tritrichomonas involves the off-label use of a poultry antibiotic called ronidazole. It is not approved by the FDA for use in cats; therefore, it must be compounded at a pharmacy into a capsule at a dose suitable for a feline patient. Because of its very unpalatable taste, it is unlikely to be compounded into a chewable or liquid oral form. Ronidazole has the potential for neurotoxicity; so, it should only be used on cats that have been confirmed positive for T. foetus. Owners must wear gloves when handling the drug. It is given once daily for two weeks, after which the diarrhea should be resolved. It is recommended that a PCR test be used at the end of treatment to confirm the total eradication of the parasites.
It should be noted that clinical remission of diarrhea has been shown to occur in many infected cats, usually by 2 years of age, even if they are not treated.