Tritrichomonas foetus is a microscopic single-celled flagellated protozoan parasite that has traditionally been identified as a cause of reproductive disease in cattle (infertility, abortion and endometritis). It has been found all over the world, but the widespread use of artificial insemination in breeding cattle has led to the virtual elimination of this organism from the cattle population in many countries including the UK and much of Europe.
Infection in Cats
There have been a number of recent studies, mostly form the USA, that have demonstrated that T foetus may also be an important cause of diarrhoea in cats. It can infect and colonises the large intestine, and can cause prolonged and intractable diarrhoea.
Studies have shown that this parasite mainly causes colitis (large bowel diarrhoea) with increased frequency of defaecation, semi-formed to liquid faeces, and sometimes fresh blood or mucus in the faeces. With severe diarrhoea the anus may become inflamed and painful, and in some cases the cats may develop faecal incontinence. Although cats of all ages can be affected with diarrhoea, it is most commonly seen in young cats and kittens, the majority being under 12 months of age. Most of the affected cats have come from rescue shelters and pedigree breeding colonies. Abdominal ultrasound examination may show corrugation of the large bowel and local lymphadenopathy. Colonic biopsies from affected cats typically show mild to severe inflammatory changes with infiltration of lymphocytes and plasma cells – a pattern commonly seen with other infectious agents and with inflammatory bowel disease. However, the parasites may be seen in close association with the mucosa. Although the diarrhoea may be persistent and severe, most affected cats are otherwise well, and show no significant weight loss.
Infection is most commonly seen in colonies of cats and multicat households, where the organism is presumably spread between cats by close and direct contact. There has been no evidence of spread from other species, or spread via food or water. In one study, 31% of cats at a cat show in the USA were identified as being infected with this organism, suggesting that this may be an important, common, and previously unrecognised cause of diarrhoea in cats.
Although most information on T foetus infection has come from studies of cats in the USA, we have identified several cases of infection in cats in the UK (mostly in young pedigree cats, and all from multicat households generally with more than one cat being affected), and it has also been identified in cats from Germany, Italy, Spain and Norway. In the UK, up to 30% of faecal samples from cats with diarrhoea are currently being found to be infected; with young pedigree cats (particularly Siamese and Bengal) being significantly more likely to be infected. The evidence therefore suggests that T foetus is probably quite widespread in cat populations, and infection is most likely where there is a high density of cats sharing the same environment.
While T foetus is known to be a significant cause of reproductive disease in cattle (infertility, abortion and endometritis), its role in causing reproductive disease in cats is still unclear. There is one report of a cat from Norway that came from a T foetus-infected household and developed pyometra (which was found to contain T foetus organisms). The cat may have been predisposed to the infection by having received six weeks of oral contraceptive (medroxyprogesterone acetate). It has also been suggested that tom cats may be able to harbour the infection in their prepuce.
Assessment of the cats faeces for the presence of T foetus can be made using a number of different methods (see below for more details); (i) looking for moving parasites in fresh faecal smears (ii) using a specific culture system or (iii) by detection of T foetus DNA using PCR. The different methods have differing sensitivities: in one study direct smears were positive in 5/36 cases, culture in 20/36, and PCR in 34/36 cases; so the PCR is by far the most sensitive test, but even this can be hampered by intermitted shedding of the parasite.
Diagnosis of T foetus infection is usually straightforward. The organism exists in the intestine as small, motile trophozoites, and these can be detected under the microscope. For optimum results, fresh faeces should be examined, and if any mucus has been passed with the faeces this is the most likely place to find the organisms. Smears of faeces/mucus diluted with some saline can be made on a microscope slide. A cover slip can be pressed over the smear and then the slide can be examined under x200 and x400 magnification. In most clinically affected cats, large numbers of the small motile organisms can be seen – they appear a little bit like microscopic tadpoles with very short tails (!), and have an undulating membrane that runs over the length of the body. Their movement is described as ‘jerky, forward motion’. Examination of multiple smears and multiple faecal samples will improve the detection of the organism. Rectal swabs can also be examined for the organism – a cotton swab can be inserted into the anus and rotated over the colonic mucosa – this is then withdrawn and a smear made on a microscope slide which is again diluted with saline and examined as above. The organism needs to be distinguished from Giardia, another protozoan parasite, but with Giardia infection the trophozoites tend to be far fewer in number, they are binucleate with a concave ventral ‘sucker’, and do not exhibit the same forward motion as T foetus. If a cat has received recent antibiotic therapy, this can suppress the number of T foetus trophozoites shed, and can make the diagnosis more difficult. In such cases, more sensitive diagnostic techniques may be preferable.
Two other diagnostic tests are available which are both more sensitive and specific for this organism. Firstly, the organism can be cultured from faecal samples using a system developed for diagnosis in cattle. The ‘In Pouchtm TF’ test (BioMed Diagnostics, Oregon, USA) uses a liquid culture system in a sterile plastic pouch. The pouch can be inoculated with 0.05g of faeces (about half the size of a small pea). The pouches are incubated at room temperature and can be examined microscopically for the motile organisms every two days for 12 days. This test is more sensitive than direct examination of faeces and helpful for detecting infections where direct smears are negative. Giardia, and other similar organisms will not grow in this specific culture medium. In the UK, this system was available from Capital Diagnostics in Edinburgh (0131 535 3145) but its high prevalence of false negatives (due to the parasite dieing in the cold UK postal system) means that it is not recommended as the PCR is far more sensitive.
The most sensitive and specific test is a PCR (polymerase chain reaction) test – a sophisticated test that can detect the presence of the genetic material of the organism. This is an extremely sensitive test that is available in the UK and US from a number of laboratories (please see below).
Current information suggests the long-term prognosis for infected cats is good, and that they will eventually overcome the infection. However, this is a slow process – in one study of infected cats, resolution of the diarrhoea took an average of nine months, with occasional cats having diarrhoea persisting for more than two years, and rarely for life. It appears that most infected cats continue to shed low levels of the organism in their faeces for many months after the resolution of the diarrhoea.
Most studies on treatment of T foetus infection in cats have been unrewarding. The organism is resistant to most traditionally used anti-protozoal drugs such as fenbendazole and metronidazole. The use of a variety of different antimicrobial drugs has been reported to improve faecal consistency during therapy of infected cats, possibly because of interaction between T foetus and the bacteria normally present in the intestine. However, such antibiotic use is not recommended as it may ultimately prolong the shedding of the organism, and does not resolve the underlying problem.
A recent study by Dr Jody Gookin at the North Carolina State University (who has performed most of the work on this infection in cats) identified that ronidazole (an antibiotic similar but not the same as metronidazole) has good efficacy against T. foetus infection in cats (JVIM, 2005 19: 436; JVIM, 2006 20: 536-543). From limited studies its use appears to be relatively safe in cats, although a small number of patients have developed neurological signs e.g. twitching and seizures, which have resolved on stopping the drug. (The neurological signs are similar to those seen in some kittens, or cats with liver disease, when they are given standard or high doses of metronidazole).
Ronidazole is not licensed for use in cats; it should only be used with caution and with informed, signed, owner consent (see Ronidazole treatment sheet for owners). Initial studies suggested that a dose of 30-50mg/kg once daily for two weeks is capable of both resolving clinical signs and potentially eradicating the T. foetus. However, keeping to the lower end of the dose is advisable (30mg/kg), as is reducing it even further for young kittens, or cats with hepatopathy; (10mg/kg once daily for two weeks). The bitterness of the powder means that it must be placed in capsules prior to administration.
Care should be exercised in the use of ronidazole; there are very few studies of its use in cats, and long-term studies in other species have suggested potential toxicity concerns (and in many countries its use in food-producing animals has been banned to minimise human exposure). Careful handling of the drug is therefore advised.
This information published with permission from http://www.fabcats.org/
Dr Andy Sparkes BVetMed PhD DipECVIM MRCVS, RCVS Specialist in Feline Medicine
Scientific Editor of the Journal of Feline Medicine & Surgery
Ellie Mardell MA VetMB CertSAM MRCVS
The Feline Centre, University of Bristol
Kirsty Wood BVSc MRCVS
The Feline Unit, Animal Health Trust
Professor Danièlle Gunn-Moore
BSc, BVM&S, PhD, MACVSc, MRCVS, RCVS Specialist in Feline Medicine
Head of Feline Clinic, University of Edinburgh