Let’s discuss an uncommon disease of cats you might not have heard of. What is trichomoniasis? What does it do? Could your cat have it? Read on to find out.

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What is Trichomoniasis?

Trichomoniasis is a gastrointestinal disease caused by the organism Tritrichomonas fetus. T. fetus is a protozoan – a single-celled parasite. The most important thing to know is that not all cats infected with T. fetus will have trichomoniasis (the disease) and show symptoms. Many will be asymptomatic (though they can still be infectious). 

The most common symptom of trichomoniasis is diarrhoea. The diarrhoea tends to be soft, yellow-green and very smelly, often described as ‘cow-pat-like’. The frequency of diarrhoea can vary from normal to almost 10 times a day. Often mucous and fresh red blood (haematochezia) will be seen. It can be painful and cause straining and flatulence when your cat tries to defecate. These symptoms can be chronic, or intermittent – some cats will even appear to get over the disease before having relapses. 

Around 1 in 5 cats will show systemic disease, including vomiting, anorexia, fever, weight loss and depression. Young cats and kittens may become faecally incontinent, look swollen and have an inflamed anus. Trichomoniasis is rarely fatal in kittens, and no adult cats have been recorded as dying from it. There have also been isolated cases where cats had a pyometra (uterus infection) with T. fetus.

Without treatment, the symptoms can persist for months or up to two years before self-resolving. Any cat with chronic diarrhoea could have trichomoniasis.  

How Do Cats Get T. fetus?

Cats get infected with T. fetus via the faecal-oral route – this is faeces infected with the parasite being ingested. This means that anything contaminated with faeces, such as food and water bowls, litter trays, fur or bedding, can spread it. Cats in close contact are more vulnerable to infection as T. fetus cannot survive long in the environment. There is no evidence it can be transmitted via sexual reproduction, unlike cattle (more on this later). One study discovered that T. fetus can be transmitted to cats from slugs that were infected with the parasite, but it is unknown if this can occur outside of a laboratory.

Once a cat ingests T. fetus, the parasite migrates to the gastrointestinal tract: mainly the latter part of the small intestines, and the large intestines. Symptoms usually start 2-7 days after infection, though again remember that many cats will show no symptoms though still release the parasite in their faeces to infect other cats. 

Any cat with diarrhoea in the same household increases the risk of other cats catching T. fetus, and if a cat has another protozoan infection, such as Giardia, they are also more likely to get T. fetus too. Any cat living with another cat diagnosed with T. fetus should also be tested for it, even if the first cat does not have diarrhoea.

Some studies have found evidence that being a male cat, living with at least two other cats, and eating raw meat all increase the risk of infection, but the study sizes were too small to prove this conclusively. 

How Do Vets Diagnose Trichomoniasis?

Diagnosing trichomoniasis can be difficult because the symptoms are commonly seen with other diseases. Your vet will start with a thorough history and clinical exam. This will often involve taking your cat’s temperature, feeling their abdomen, checking their alertness and hydration, and more. Trichomoniasis cannot be definitively diagnosed this way, and other diseases such as Giardia, roundworms or inflammatory bowel disease may also be considered. 

Stool sampling is the most common method for identifying T. fetus. Diarrhoea is collected by the cat’s owner or taken directly from the intestines by a vet via a flushing technique. The samples are diluted and looked at under a microscope. The parasite Giardia looks very similar to T. fetus but experienced microbiologists can observe how they move differently to distinguish the two. If there are not enough parasites to see in the sample the faeces may be cultured to grow more. The faeces can also be tested for the DNA/RNA of T. fetus via PCR testing.

The best way to diagnose trichomoniasis is histopathology, where a piece of tissue from a cat’s intestines are removed via endoscopy or surgery, under anaesthetic. Special tests are performed on the tissue to show the parasite.

Unfortunately, not finding evidence of T. fetus does not rule out infection, so it should always be a consideration for cats with chronic diarrhoea unless another disease is identified as the cause. 

Exactly how is Trichomoniasis Treated?

Treatment of trichomoniasis can be difficult. Historically, cats were given a wide range of antibiotics and many seemed to respond to this treatment. However, once antibiotics were stopped the symptoms often returned. We think this is because the bacteria T fetus were feeding off were killed instead – once the antibiotics were stopped the bacterial populations grew, and the T. fetus population rebounded. This method of treatment is not recommended anymore as it is not effective and can contribute to antimicrobial resistance. 

The most effective drug against T. fetus is ronidazole, an antibiotic similar to the more common metronidazole. It is not licensed for use in cats, but tablets can be prescribed by vets using the cascade. The recommended treatment is a course given once a day for 14 days. Care must be taken to dose correctly, as higher dose of the drug can cause neurological problems, particularly in kittens, or cats with liver disease. Some studies have found the use of probiotics may reduce the dose of ronidazole needed.

Symptoms can persist for a few weeks beyond the treatment duration, so cats must be isolated during this time to prevent them infecting other cats. Strict hygiene should be implemented during this period too. Unfortunately, relapses of the disease are not uncommon, and a second course of ronidazole may be needed to fully clear the infection. 

Is There Any Association With Cows?

Yes. In fact, T. fetus is a serious reproductive disease of cattle. It infects bulls, in which it causes no symptoms, who then spread it to cows via sexual reproduction or close contact. Cows infected with T. fetus can become infertile, have pyometras or even abort their calves.

However, we are unsure how closely linked trichomoniasis in cats and cattle are. Laboratories have managed to infect cats with T. fetus from cattle, and vice-versa, but we don’t know if this can happen in real-life settings. It seems unlikely, and one study even advised that T. fetus in cats should be considered a different species, Tritrichomonas blagburni.

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