Edited October, 2018


The Tritrichomoniasis guidelines were first published in the J Feline Med Surg 2013; 15: 647-649 by Tim Gruffydd-Jones et al. The present guidelines were updated by Séverine Tasker.





Tritrichomonas is a protozoan organism that can cause large bowel diarrhoea in cats. It is specific to cats, distinct from other tritrichomonas species and not considered to be zoonotic. Infection is most common in young cats from multicat households, particularly pedigree breeding catteries. Affected cats show frequent foetid diarrhoea, often with mucus, fresh blood and straining, but generally remain bright and do not lose weight. Diagnosis of infection is usually based on direct microscopic examination of freshly voided faeces. PCR testing is more sensitive but may detect infections unrelated to diarrhoea and therefore requires care in interpretation. The treatment of choice is ronidazole, which should be used with care as it is an unlicensed drug for cats with a narrow safety margin. Clinical signs are generally self-limiting in untreated cases but may take months to resolve.



Fig. 1 Tritrichomonas (T.) foetus, stained with Lugol’s iodine. Three anterior flagellae can be seen, and an undulating membrane runs the length of the body. (Courtesy

Fig. 1 Tritrichomonas foetus, stained with Lugol’s iodine. Three anterior flagellae (“tri”) can be seen, and an undulating membrane runs the length of the body. (Courtesy




Tritrichomonas (T.) foetus is a highly motile flagellate protozoan parasite (Fig. 1) that resides in the large intestine of cats, where it causes a pathology (Gookin et al., 1999, 2001; Levy et al., 2001, 2003). It is distinct from Pentatrichomonas hominis, which infects humans (Levy et al., 2003). T. foetus is also recognized as a parasite of the reproductive tract of cattle. However, Tritrichomonas isolated from cats does not cause the same pathology as bovine isolates in experimental infection of cattle, and vice versa. Furthermore, recent molecular studies have identified sequence differences between feline and bovine isolates suggesting they are distinct strains, or even species, and a new name of Tritrichomonas blagburni has been proposed for the feline species (Walden et al., 2013), although this terminology is not yet widely accepted (Yao and Koster, 2015), and T. foetus will be used for the remainder of these guidelines.



Life cycle

During replication in the mucus of the large intestine, trophozoites are produced by binary fission and excreted in the faeces. No oocyst form exists for Tritrichomonas. Transmission occurs via the faecal-oral route. The trophozoites have very limited ability to survive outside the cat and do not persist in the environment.




Prevalence studies have given variable results, depending upon the test used, but the background of the cats is also an important variable. Surveys based on PCR testing give the highest prevalence, sometimes over 70%. This makes it difficult to show an association between infection and signs of diarrhoea; the test may detect infections not associated with the clinical picture. In other studies a figure of up to 30% has been found, but when comparing the prevalence in cats with clinical signs with that in healthy cats from the same background, there has not always been a clear difference. Infection is more common in cats from multicat environments, particularly from breeding colonies, and in some studies purebreds are at increased risk of infection (Yao and Koster, 2015). Groups may be affected, but also single cats within the household. Infection is generally more common in young cats, with most studies reporting increased levels of T. foetus infection in cats of 1 year of age or less (Yao and Koster, 2015). A survey in Canada reported an association between infection and attendance at cat shows (Hosein et al., 2013). Recently a review article has summarised the varied T. foetus prevalences found worldwide (Yao and Koster, 2015), with T. foetus reported in Europe, North America, Australia, New Zealand and Asia. Infections in South American cats have also now been documented (Hora et al., 2017, Duarte et al., 2018).

Studies in Europe have concentrated on cats with chronic diarrhoea, and T. foetus has indeed been detected in the faeces of up to 39% of cats in the UK, Austria, Greece, Italy, Spain, Switzerland, and the Netherlands (Arranz-Solis et al., 2016; Burgener et al., 2009; Frey et al., 2009; Gookin et al., 2004; Gunn-Moore et al., 2007; Holliday et al., 2009; Kuehner et al., 2011; Mardell and Sparkes, 2006; Paris et al., 2014; Steiner et al., 2009; van Doorn et al., 2009; Xenoulis et al., 2010).




The mechanism by which Tritrichomonas induces diarrhoea is not clear. It resides in the mucus on the mucosal surface of the large intestine and adherence factors may be important. The organism may produce toxins and induces an inflammatory response in the colon. Recently, the cysteine protease CP30 has been identified as a potential virulence factor in T. foetus-induced adhesion-dependent cytotoxicity in the feline intestine, and could be targeted for future treatment strategies (Gould et al., 2017).



Clinical signs

Not all infections are associated with clinical signs. The parasite targets the large bowel, and the features of the diarrhoea are usually suggestive of colitis, with frequent passage of small quantities of liquid to semi-formed faeces, often with blood, mucus and some straining. In one recent study the median duration of diarrhoea was 135 days (Xenoulis et al., 2013). Some affected cats develop faecal incontinence. Sometimes anorexia and depression are reported (Xenoulis et al., 2013). The parasite has been found in the genital tract of cats but does not appear to be linked to reproductive disease, although a case of pyometra in association with T. foetus infection of the uterus has been reported (Dahlgren et al., 2007).  Interestingly a recent report (Pazzini et al., 2018) documented the presence of T. foetus in the nasal cavity of a cat with chronic purulent nasal discharge, in association with Mycoplasma felis, although more work is required to elucidate the pathogenicity of the agent in this anatomical location.




Little is known about the immunity to Tritrichomonas. Infections generally resolve, which suggests that infected cats develop an effective immune response.




The organism can be identified in fresh faeces by direct examination, which reveals the motile trophozoites. The single flagellum induces a jerky forward motion that can aid in differentiation from the trophozoites of giardia. If mucus is passed with the faeces, this represents a good sample for examination. Faeces are suspended in saline and examined under a cover slip at x200-400. Infection can also be diagnosed using PCR, which is now widely available, and by culturing the organism, for which the “InPouch” culture system is used. There are marked differences in the sensitivity of the different diagnostic tests; 14.7% for trophozoite examination and 58.8% for the InPouch culture system (Yao and Koster, 2015). PCR may have the disadvantage of identifying infections, which are not clinically relevant; detection of trophozoites in faecal smears, or culture of the organism may be the best tests for identifying cases for which treatment is indicated, although a positive PCR result in the presence of signs that can be associated with T. foetus infection is usually adequate for diagnosis. Diarrhoeic faecal samples are preferable to increase sensitivity for testing for T. foetus by all of the above methods. Colonic flushing is an excellent method that can be used to obtain samples for T. foetus testing, and can be performed relatively easily in a conscious cat. A lubricated soft catheter is inserted into the cat’s rectum into the colon and flushed with around 10 ml of sterile saline; as much of the fluid as possible is reaspirated and submitted for testing. An online video of this technique is available at (Gookin, 2018), along with other excellent resources on the diagnosis of infection (Gookin and Dybas, 2018), which have been written for owners but which contain excellent information for veterinary surgeons. Trophozoites may be difficult to identify on histopathological examination of colonic biopsies.




The drug of choice is ronidazole, a nitroimidazole related to metronidazole. It is not licensed for use in cats and experience is limited, although it appears to be effective. Informed signed owner consent should be obtained before use. It can be obtained as a powder and formulated in capsules, and tablets are now available from specialist veterinary pharmaceutical companies. There has been recent debate about the appropriate dose – currently 30mg/kg daily orally for 2 weeks is recommended. This is lower than some previous recommendations but reduces the risk of side effects (neurotoxicity as with metronidazole). However, relapses can occur. Preliminary data suggest that the addition of a probiotic to ronidazole therapy may reduce the likelihood of T. foetus relapse (Lalor and Gunn-Moore, 2012). Initial experience indicated that metronidazole is not effective, but this finding needs to be reviewed. The diarrhoea will usually resolve spontaneously in untreated cats although this may take months or longer.

A key unanswered question when infection is identified in a group of cats is which cats should be treated – all animals in a group or just cats with diarrhoea. A reasonable approach is to treat only cats that are showing signs and are positive on faecal smears.

Excellent resources on the treatment of T. foetus infection are available at (Gookin and Dybas, 2018). These guidelines have been written for owners but contain excellent information for veterinary surgeons, and consultation and reference to these guidelines is suggested if further information on treatment of T. foetus is required.






Arranz-Solis D, Pedraza-Diaz S, Miro G, Rojo-Montejo S, Hernandez L, Ortega-Mora M, Collantes-Fernandez E (2016): Tritrichomonas foetus infection in cats with diarrhea from densely housed origins. Vet Parasitol 221, 118-122.


Burgener I, Frey C, Kook P, Gottstein B (2009): Tritrichomonas fetus: a new intestinal parasite in Swiss cats. Schweiz Arch Tierheilkd 151, 383-389.


Dahlgren SS, Gjerde B, Pettersen HY (2007): First record of natural Tritrichomonas foetus infection of the feline uterus. J Small Anim Pract 48, 654-657.


Duarte RP, Rocha PRDA, Nakamura AA, Cipriano RS, Viol MA, Melo GD, Meireles MV, Machado GF (2018): Detection of natural occurrence of Tritrichomonas foetus in cats in Aracatuba, Sao Paulo, Brazil. Pesqui Vet Brasil 38, 309-314.


Frey CF, Schild M, Hemphill A, et al (2009): Intestinal Tritrichomonas foetus infection in cats in Switzerland detected by in vitro cultivation and PCR. Parasitol Res 104, 783-788.


Gookin J. Accessed 9th September 2018. T. foetus Diagnostic Laboratory


Gookin JL, Breitschwerdt EB, Levy MG, Gager RB, Benrud JG (1999): Diarrhea associated with trichomonosis in cats. J Am Vet Med Assoc 215, 1450-1454.


Gookin J, Dybas D. Accessed September 9th 2018. An owner’s guide to diagnosis and treatment of cats infected wtih Tritrichomonas foetus.


Gookin JL, Levy MG, Law JM, Papich MG, Poore MF, Breitschwerdt EB (2001): Experimental infection of cats with Tritrichomonas foetus. Am J Vet Res 62, 1690-1697.


Gookin JL, Stebbins ME, Hunt E, et al (2004): Prevalence of and risk factors for feline Tritrichomonas foetus and Giardia infection. J Clin Microbiol 42, 2707-2710.


Gould EN, Giannone R, Kania SA, Tolbert MK (2017): Cysteine protease 30 (CP30) contributes to adhesion and cytopathogenicity in feline Tritrichomonas foetus. Vet Parasitol 244, 114-122.


Gunn-Moore DA, McCann TM, Reed N, Simpson KE, Tennant B (2007): Prevalence of Tritrichomonas foetus infection in cats with diarrhoea in the UK. J Feline Med Surg 9, 214-218.


Holliday M, Deni D, Gunn-Moore DA (2009): Tritrichomonas foetus infection in cats with diarrhoea in a rescue colony in Italy. J Feline Med Surg 11, 131-134.


Hora AS, Miyashiro SI, Cassiano FC, Brandao PE, Reche A, Pena HFJ (2017): Report of the first clinical case of intestinal trichomoniasis caused by Tritrichomonas foetus in a cat with chronic diarrhoea in Brazil. BMC Vet Res 13.


Hosein A, Kruth SA, Pearl DL, Richardson D, Maggs JC, Peach HA, Peregrine AS (2013): Isolation of Tritrichomonas foetus from cats sampled at a cat clinic, cat shows and a humane society in southern Ontario. J Feline Med Surg 15, 706-711.


Kuehner KA, Marks SL, Kass PH, Sauter-Louis C, Grahn RA, Barutzki D, Hartmann K (2011): Tritrichomonas foetus infection in purebred cats in Germany: prevalence of clinical signs and the role of co-infection with other enteroparasites. J Feline Med Surg 13, 251-258.


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.


Levy MG, Gookin JL, Poore MF, Litaker RW, Dykstra M (2001): Information on parasitic gastrointestinal tract infections in cats. J Am Vet Med Assoc 218, 194-195.


Levy MG, Gookin JL, Poore M, Birkenheuer AJ, Dykstra MJ, Litaker RW (2003): Tritrichomonas foetus and not Pentatrichomonas hominis is the etiologic agent of feline trichomonal diarrhea. J Parasitol 89, 99-104.


Mardell EJ, Sparkes AH (2006): Chronic diarrhoea associated with Tritrichomonas foetus infection in a British cat. Vet Rec 158, 765-766.


Paris JK, Wills S, Balzer HJ, Shaw DJ, Gunn-Moore DA (2014): Enteropathogen co-infection in UK cats with diarrhoea. BMC Vet Res 10, 13.


Pazzini L, Mugnaini L, Mancianti F, Ressel L (2018): Tritrichomonas foetus and Mycoplasma felis coinfection in the upper respiratory tract of a cat with chronic purulent nasal discharge. Vet Clin Path 47, 294-296.


Steiner JM, Xenoulis PG, Read SA, et al (2009): Identification of Tritrichomonas foetus DNA in feces from cats with diarrhea from Germany and Austria. J Vet Intern Med 21, 649. [abstract].


van Doorn DC, de Bruin MJ, Jorritsma RA, Ploeger HW, Schoormans A (2009): Prevalence of Tritrichomonas foetus among Dutch cats. Tijdschr Diergeneeskd 134, 698-700.


Walden HS, Dykstra C, Dillon A, Rodning S, Givens D, Bird R, Newton J, Lindsay D (2013): A new species of Tritrichomonas (Sarcomastigophora: Trichomonida) from the domestic cat (Felis catus). Parasitol Res 112, 2227-2235.


Xenoulis PG, Lopinski DJ, Read SA, Suchodolski JS, Steiner JM (2013): Intestinal Tritrichomonas foetus infection in cats: a retrospective study of 104 cases. J Feline Med Surg 15,1098-1103.


Xenoulis PG, Saridomichelakis MN, Read SA, Suchodolski JS, Steiner JM (2010): Detection of Tritrichomonas foetus in cats in Greece. J Feline Med Surg 12, 831-833.


Yao CQ, Koster LS (2015): Tritrichomonas foetus infection, a cause of chronic diarrhea in the domestic cat. Vet Res 46, 35.


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