Tritrichomonas foetus infection in cats

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). This parasite 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 from the USA, that have demonstrated that this parasite may be an important cause of diarrhoea in cats. In cats, T foetus infects 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 defecation, 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 (enlarged lymph nodes). Colonic biopsies from affected cats typically show mild to severe inflammatory changes with predominantly 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 presumably the organism is 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, several cases of infection have been identified 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 (pus within the uterus - 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

Diagnosis of T foetus infection is usually quite straightforward and involves assessing the cat's faeces for the presence of T foetus. This can be done 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 polymerase chain reaction (PCR). The most sensitive and specific test is a PCR test – a sophisticated test that can detect the presence of the genetic material of the organism.

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, eg, 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 30-50 mg/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 (30 mg/kg), as is giving it only once daily, and reducing it even further for young kittens, or cats with hepatopathy; (10 mg/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.

There is a treatment available for T foetus (ronidazole), which is not licensed for use in cats, and is difficult to obtain and has toxicity concerns. For these reasons, treatment needs to be discussed in detail with your vet.

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 measures to avoid ingesting the parasite. These measures 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 not to keep cats that have persistent diarrhoea. If their cat develops diarrhoea it should be fully investigated and if found to be infected with T foetus it should be treated with ronidazole and then re-tested, or (at least temporarily) rehomed until the infection has resolved.

Capital Diagnostics, SAC Veterinary Science Division, Bush Estate, Penicuik, Midlothian, EH26 0QE: Tel. 0131 535 3145).

A real-time quantitative PCR (QPCR) assay is now also available, which incorporates an internal amplification control so that false negative results are avoided. The assay is performed on a small volume of faeces (2-5ml) at a cost of £29 (+VAT); further details on the test and submission forms can be found on http://www.langfordvets.co.uk/lab_pcrnews.htm or by contacting Langford Veterinary Services Diagnostic Laboratories at the University of Bristol, Langford House, Langford, Bristol, BS40 5DU. Tel: +44 (0)117 928 9412 Fax: +44 (0)117 928 9613 Email: lvs@langfordvets.co.uk

In the US 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

Rectal smears can be made using cotton swabs rolled over the rectal wall. Smears can be made on glass slides, and material obtained should be diluted with saline to prevent desiccation.

Typical appearance of a large number of T foetus organisms in a faecal smear under x400 magnification. When examined, the organisms can be seen to be highly motile.

Appearance of an individual T foetus organism stained with Lugol's iodine. Three anterior flagellae can be seen, and an undulating membrane runs the length of the body.