Tritrichomonas Foetus

Tritrichomonas foetus is a single-celled microscopic protozoan parasite of cats and cattle. It causes the disease trichomoniasis. Some researchers refer to the species in cats as Tritrichomonas blagburni

Tritrichomonas foetus infects the reproductive organs of cattle. In cows, it causes fertility issues including:

• infertility;
• pyometra (infection of the uterus);
• death of the embryo or abortion.

It is asymptomatic in bulls. T. foetus is spread venereally via sexual reproduction or close contact from the bull to the cow. trichomoniasis outbreaks in a herd and the subsequent drop in fertility can cause severe financial loss for cattle farmers – the use of artificial insemination and vaccination can reduce this risk.

Studies have found that in laboratory settings T. foetus from cats can infect cattle (and vice-versa) resulting in similar but not identical diseases. It is unknown how likely it is for the parasite to spread between the two species in the wild – some researchers claim it is unlikely, and a subsequent study has even put forward the parasite in cats should be considered a different species, Tritrichomonas blagburni, due to these differences.

Tritrichomonas foetus infects the gastrointestinal tracts of cats, mainly the last part of the small intestines and the beginning of the large intestines. It is believed to be spread mainly via the faecal-oral route from litter trays, contaminated food and water bowls, close contact and the environment. Unlike other similar parasites (e.g. Giardia), T. foetus cannot survive for long periods in the environment. There have been only a few cases where T. foetus has been found in the reproductive tract of cats and has caused pyometra. It is unclear whether it can be transmitted venereally as in cattle. Unlike other protozoan parasites, there is no evidence T. foetus can be found normally in a cat’s GI tract as a commensal organism. One study found that T. foetus can be transmitted from slugs artificially infected with the parasite, but it is unknown if cats can be infected via slugs naturally either.

Cats infected with T. foetus have been identified in Europe, North America and Asia. Some studies initially identified younger cats as being more vulnerable to infection, but this does not always appear to be the case. Any cat with diarrhoea in the house (either due to T. foetus or another disease) raises the risk of other cats becoming infected. Infection with other protozoal parasites also increases the risk of T. foetus infection.

There has also been limited evidence demonstrating that being male, sharing a house with at least two other cats, and eating raw food all increase the risk of infection, but the study sizes have been too small to prove these associations yet. However, the condition is most common in younger cats and those from colony conditions (large pedigree breeding colonies and rescue cats)

As it lives in the latter part of the intestines, T. foetus tends to cause disease here. However, some cats infected with T. foetus show no clinical signs of disease. These cats can still shed the parasite in their faeces, thus can be infectious though they themselves are not unwell.

Clinical signs of trichomoniasis usually start 2-7 days post-ingestion of the parasite. For cats showing symptoms, the most common symptom is soft yellow-green smelly ‘cow-pat’ diarrhoea from the large intestine. This can be produced a normal amount or up to eight times a day. Mucus and fresh red blood are commonly seen too. Often the cat will strain when passing faeces, and there may be flatulence. If not treated, the diarrhoea can persist for months, in some cases up to two years, before the disease ends. Diarrhoea can be constant or intermittent during this time. Some cats will appear to recover, then have a brief but severe relapse of diarrhoea.

Around 20% of cats will show systemic symptoms such as weight loss, vomiting, going off their food, a fever and depression. Young kittens can also have faecal incontinence, swelling and an inflamed anus. trichomoniasis is rarely fatal, and only reported in kittens.

Any cat with chronic large intestinal diarrhoea (determined by a vet) could have a T. foetus infection. A thorough history and physical exam by a vet is a good starting point, focussing particularly on the type of diarrhoea the cat has. Remember that many cats will be systemically healthy.

The most common condition that may be confused for T. foetus is Giardia, a similar parasite. Giardia causes small intestinal diarrhoea, which may be able to be distinguished by a vet based on history. No research has yet demonstrated any usefulness with blood testing in diagnosing T. foetus, while ultrasonography shows non-specific corrugation of the large intestine and enlargement of nearby lymph nodes, which may also be seen with many other intestinal conditions.

Faecal tests are the preferred method of diagnosing trichomoniasis. Samples of diarrhoea can be collected by an owner or can be taken directly from the intestines via flushing by a vet. Diagnosis can sometimes be made by looking at a sample under a microscope to view the parasites. Giardia and T. foetus look similar under a microscope, but a skilled microbiologist can differentiate the way the parasites move in liquid. Faeces are sometimes cultured to grow more parasites, increasing the chances of viewing one under a microscope.

If further testing is needed, faecal samples can be tested for the genetic material (either DNA or RNA) of T. foetus via PCR testing, and antigens to Giardia via ELISA testing. Unfortunately, not finding the DNA/RNA of T. foetus does not always rule out infection. Remember that cats can - and frequently do - have infections with both parasites.

The gold standard for diagnosis is via histopathology. This involves taking a biopsy from a cat’s bowels, usually under general anaesthetic via endoscope or surgery. A biopsy will show the effects of colitis due to infection, as well as the parasite itself. Special tests are needed to view the parasites in tissue. Again, not finding T. foetus does not rule out infection.

In many cases, treatment is not required as the cat is asymptomatic; and in almost all cases it will resolve on its own eventually. If the diarrhoea is minor and manageable, then supportive treatment with diet and probiotics/prebiotics may be sufficient.

The treatment of T. foetus requires antimicrobial drugs. Some cats with chronic diarrhoea are given antibiotics – it has been noted that those with trichomonas often respond initially to treatment and the diarrhoea improves, but the diarrhoea then returns once treatment has stopped. It has been theorised that this is because antibiotics will kill bacteria the parasites feed off of, thus reducing their population.

The drug shown to be most effective against T. foetus is ronidazole, a drug similar to the more common antibiotic metronidazole. T. foetus is likely to be resistant to metronidazole as it rarely treats the infection. Unfortunately, ronidazole is not licensed for use in cats so must be used off licence. Treatment is given orally, usually got for 14 days. The drug has not been widely tested in cats, and can cause toxicity at higher doses, causing neurological signs, so care must be taken to dose correctly. The use of a probiotic alongside may reduce the dose of ronidazole needed and the chance of relapse. The lowest dose is recommended for young kittens or cats with liver disease. Other antiprotozoal drugs have been tested with mixed results.

Diarrhoea can persist for a few weeks after treatment as the intestines heal. Infected cats should be isolated from other cats until this resolves. Treatment is not always effective due to resistance of T. foetus. Remember that T. foetus tends to resolve after a maximum of two years without treatment, so if the cat is well and the owner can manage the diarrhoea, treatment may not be necessary.

Relapses are not uncommon, so careful monitoring and the possibility of a second course of treatment should be expected. All cats in the house are likely to be at risk from T. foetus infections too, so should be tested as well, even if they do not have diarrhoea. Ensuring that litter trays and surfaces are regularly cleaned will reduce the risk of transmission.