Edited December, 2016
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.
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.
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 the symptom 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 recent 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.
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.
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.
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 becoming more 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. Diarrhoeic faecal samples are preferable for testing for T. foetus by the above methods, and colonic flushing can be used to obtain samples. 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 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.
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