Tritrichomonas foetus

Dr Emi Barker BSc (Hons) BVSc (Hons) PhD DipECVIM-CA MRCVS 

Published April 2019 

Reviewed September 2021


Tritrichomonas foetus is a single-celled protozoan parasite that lives within mucus covering the mucosa surface of the distal ileum, caecum and colon of cats. Infection causes inflammation of the mucosa resulting in predominantly large intestinal diarrhoea. Risk factors include young age and coming from a multi-cat / breeding household. Transmission is via the faeco-oral route, with organisms remaining viable in moist faeces for a small number of days.

Different strains of T. foetus infect the reproductive tract of cattle and colonise the nasal mucosa and gastrointestinal tract of pigs. This agent is rarely zoonotic, but good hygiene practice should be applied when handling infected cats or their waste products particularly by immunosuppressed individuals.


Clinical signs

Although cats of any age can be affected, younger cats are over represented. Most cats are presented with a chronic history of waxing and waning, malodourous, large intestinal diarrhoea with variably increased frequency, increased mucus, haematochezia, tenesmus, and flatulence. In some cats this can progress into faecal incontinence, perianal swelling and dermatitis. Cats are often otherwise well in themselves.



Diagnosis is based on direct microscopic visualisation of organisms, culture (using the ‘InPouch’ system), or detection of organism DNA by PCR in faeces, faecal mucus or colonic wash. Microscopically, Trichomonas organisms have a similar size and shape to Giardia spp., but with a different movement pattern (T. foetus is rapid and jerking; Giardia spp. is slow, with a falling-leaf movement). False negative results can occur with all methodologies, therefore, as the colonic mucus is the site of infection PCR of colonic wash fluid increases the sensitivity of detection in infected cats (description and images available in Gookin and others 2017).


Treatment and prevention

Although clinical signs may improve on antibiotics, diarrhoea typically recurs when these are stopped. Feeding of bland or high-fibre diets have also been suggested to be beneficial. Clinical signs can resolve without treatment but affected cats likely remain a reservoir of infection.

The only agent with proven efficacy against T. foetus is ronidazole, which is effective in around two thirds of cases (Xenoulis and others 2013). Current recommended doses are 20-30mg/kg orally once daily for 14 days and should be based on accurate weight measurement (Gruffydd-Jones and others 2013). In young kittens (not £12 weeks age) or cats with hepatic dysfunction doses should be reduced to 10mg/kg to minimise risk of adverse effects. Administration of a probiotic (e.g. Pro-Kolin Enterogenic, Protexin) for four weeks is also recommended (Lalor & Gunn-Moore 2012).

Adverse effects of ronidazole are primarily related to neurotoxicity (lethargy, inappetence, ataxia, tremors, and seizures) with vomiting less frequent. If adverse effects were to manifest, the ronidazole should be immediately discontinued. Metronidazole increases the risk of toxicity, so should not be given concurrently. As it is teratogenic, ronidazole should not be administered to pregnant or nursing queens. Obtaining informed, written, owner consent prior to treatment is strongly recommended and owners should wear gloves when administering.

At time of writing ronidazole is not available as a licensed product for use in cats. Only two UK compounding pharmacies supply reformulated capsules or liquid direct to veterinary practices – Nova Laboratories ( and Summit Veterinary Pharmaceuticals (

To reduce the risk of re-infection and transmission, good hygiene practice (e.g. frequent litter tray emptying and cleaning) should be employed and ideally infected cats isolated. The risks and benefits of treating all cats within a household in should be considered carefully.

Read our surveillance report with a focus on T. foetus here.


GOOKIN, J. L., HANRAHAN, K. & LEVY, M. G. (2017) The conundrum of feline Trichomonosis. Journal of Feline Medicine and Surgery 19, 261-274

GRUFFYDD-JONES, T., ADDIE, D., BELAK, S., BOUCRAUT-BARALON, C., EGBERINK, H., FRYMUS, T., HARTMANN, K., HOSIE, M. J., LLORET, A., LUTZ, H., MARSILIO, F., MOSTL, K., PENNISI, M. G., RADFORD, A. D., THIRY, E., TRUYEN, U. & HORZINEK, M. C. (2013) Tritrichomoniasis in cats: ABCD guidelines on prevention and management. Journal of Feline Medicine and Surgery 15, 647-649

GUNN-MOORE, D. A., MCCANN, T. M., REED, N., SIMPSON, K. E. & TENNANT, B. (2007) Prevalence of Tritrichomonas foetus infection in cats with diarrhoea in the UK. J Feline Med Surg 9, 214-218

LALOR, S., GUNN-MOORE, D (2012): Effects of concurrent ronidazole and probiotic therapy in cats with Tritrichomonas foetus-associated diarrhoea. (Abstract). J Feline Med Surg 14, 651

PAYNE, P. A. & ARTZER, M. (2009) The biology and control of Giardia spp and Tritrichomonas foetus. Veterinary Clinics: Small Animal Practice 39, 993-1007

XENOULIS, P. G., LOPINSKI, D. J., READ, S. A., SUCHODOLSKI, J. S. & STEINER, J. M. (2013) Intestinal Tritrichomonas foetus infection in cats: a retrospective study of 104 cases. Journal of Feline Medicine and Surgery 15, 1098-1103