Here it is, you may have already seen it - if so sorry for the long post.
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 do not show 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.
Diagnosis
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 quite 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 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 Caroline State University (USA) for this test – information on this is available at:
www.cvm.ncsu.edu/mbs/gookin_jody.htm.
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 diarrhoea took an average of nine months, with occasional cats having diarrhoea 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 faeces for many months after the resolution of the diarrhoea.
Treatment
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) may have good efficacy against T. foetus infection in cats (JVIM, 2006;20;536). 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). However, ronidazole is not licensed for use in cats; it should only be used with caution and with informed, signed, owner consent. Initial studies suggested that a dose of 30-50mg/kg once to twice 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 giving it only once daily, and reducing it even further for young kittens or cats with hepatopathy; (10mg/kg once daily for two weeks). To ensure that each kitten receives the correct dose, and so reduce the risk of side effects, it is also important to weigh the kittens prior to ordering the reformulated capsules. The bitterness of the powder means that it must be placed in capsules prior to administration.
Ronidazole (10% powder preparation) is commonly used to treat trichomoniasis in birds (e.g. pigeons). However, it is not available in this form in the UK, and the consistency of the 10% formulation is difficult to guarantee. Therefore, we have gained permission from the Veterinary Medicines Directorate (VMD) to use 100% pure chemical grade ronidazole to treat T. foetus infected cats. This is the form that is now used in the USA. In the UK it can be obtained upon receipt of a signed named-animal prescription as capsules from Nova Laboratories, Tel: 0116 223 0099. While the VMD have agreed to our use of this chemical in these cats, they strongly recommend that detailed records are maintained and that no cat is treated without first obtaining informed, signed, owner consent. In addition, we should compile data on all potential adverse effects: send case information on any potential adverse effects to Danielle.Gunn-Moore@ed.ac.uk.
Care should be exercised in the use of ronidazole, as there are very few studies of its use in cats, and long-term studies in other species have suggested some potential toxicity concerns. (In many countries its use in food-producing animals has been banned to minimise human exposure). Careful handling of the drug is therefore advised. It should never be given to pregnant queens (or queens about to be put to stud): it is very teratogenic and may result in a number of different and severe defects.
Since the diarrhoea does resolve over time, and is often more of an inconvenience than being associated with significant adverse effects in affected cats, it may not be necessary or advisable to treat all affected cats with ronidazole. Using a simple highly digestible diet or a high fibre diet may result in improved faecal consistency, and this may be sufficient to control the clinical signs in some cats.
Can T. foetus infect people?
It is thought that T. foetus is unlikely to infect humans; however as a precaution people in contact with infected cats are advised to take basic hygiene precautions to avoid ingesting the parasite. These precautions will also help to prevent the spread of the infection to other cats, and prevent humans from being infected with other infections that the cat may carry.
Suitable hygiene precautions include:
Washing hands thoroughly after handling cat faeces
Washing hands thoroughly after cleaning cat litter trays, whether the cat has diarrhoea or not
Cat scratches or bites should always be washed immediately with soap and water. Seek medical attention as soon as possible if signs of infection appear, such as redness, pain or swelling.
Persons with a weakened immune system should not handle their cat’s faeces or litter box, they are advised to wash their hands after handling their cats, and they are advised not to keep cats that have persistent diarrhoea. If their cat develop diarrhoea it should be fully investigated and if found to be infected with Tritrichomonas foetus it should be treated with ronidazole and then re-tested, or (at least temporarily) re-homed until the infection has resolved
