Thread: Tritrichomonas Foetus

Tritrichomonas Foetus, also referred to as "Tritrich", "T. Foetus" and "TF" is a microscopic single-celled flagellated (having whip-like appendages) protozoan parasite that has traditionally been identified as an STD in cattle. 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 in the USA, that have demonstrated that T foetus may also be an important cause of diarrhea in cats. It can infect and colonize in the large intestine, and can cause prolonged and intractable diarrhea. Although the diarrhea may be persistent and severe, most affected cats are otherwise well, and do not show significant weight loss.

Studies have shown that this parasite mainly causes colitis (large bowel diarrhea) with increased frequency of defecation, semi-formed to liquid feces, and sometimes fresh blood or mucus is found in the feces. With severe diarrhea the anus may become inflamed and painful,and in some cases the cats may develop fecal incontinence. Although cats of all ages can be affected with diarrhea, 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 catteries. 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 unrecognized cause of diarrhea 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 fecal samples from cats with diarrhea 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.

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.

Diagnosis

Assessment of the cats feces 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 fecal smears (not as effective as other means, because they are so microscopic)
(ii) using a specific culture system (referred to as a "pouch test")
(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
Diagnosis of T foetus infection is usually quite straightforward. The organism exists in the intestine as small, motile trophozoites, and these can be detected under the microscope. For optimum results, fresh feces should be examined, and if any mucus has been passed with the feces this is the most likely place to find the organisms. Smears of feces/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 fecal 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 fecal 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 feces (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 feces 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 by 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 from Capital Diagnostics in Edinburgh (Capital Diagnostics, SAC Veterinary Science Division, Bush Estate, Penicuik, Midlothian, EH26 0QE: Tel. 0131 535 3145). Alternatively, samples can be submitted to the College of Veterinary Medicine, North Carolina State University (USA) for this test – information on this is available at: gookin_jody.html. [I, Rozsmom, had the DNA tests done through my vet in Massachusetts, sent to a medical lab in Boston]

Prognosis

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 diarrhea took an average of nine months, with occasional cats having diarrhea persisting for more than two years, while in others it resolved after two months. It appears that most infected cats continue to shed low levels of the organism in their feces for many months after the resolution of the diarrhea.

(Continued in next post)