The feline organism is now also called Tritrichomonas blagburni. The older name T. foetus still appears in research and laboratory reports. Feline intestinal infection should not be confused with bovine reproductive trichomonosis or human sexually transmitted trichomoniasis.
When to see a vet urgently
Do not assume a long-term intestinal infection alone explains a clear deterioration in general condition:
- diarrhoea occurs with marked lethargy, not eating or repeated vomiting;
- a kitten in particular weakens or cannot drink normally;
- stools contain substantial blood or defecation is very painful;
- unsteadiness, tremors, unusual behaviour or seizures begin during treatment.
Contact a vet immediately in these situations. You can find a vet near you. Report neurological signs during ronidazole treatment immediately and do not give the next dose before veterinary instructions.
Overview
Tritrichomonas foetus is a single-celled flagellated parasite that damages the large intestinal lining. Infection causes inflammation, disturbed gut microbiota and chronic diarrhoea. Unlike many other intestinal parasites, trichomonads respond poorly to ordinary antiprotozoal medicines, and disease can last for months.
The parasite lives in mucus on the intestinal lining. It can irritate the large intestine, causing frequent defecation and fresh blood or mucus in stools. However, not every infected cat has symptoms. Good appetite or intermittently firmer stools therefore do not prove infection has ended.
Tritrichomonas does not have a resistant cyst stage like Giardia. It tolerates drying poorly but can survive for a time in moist faeces. Reducing faecal contamination is therefore central to control, rather than medication of the affected cat alone.
Causes
- infection through contact with infected animals' faeces;
- shared litter trays and bowls;
- crowded conditions in breeding establishments or shelters;
- inadequate hygiene and disinfection.
Infection occurs when the parasite passes from faeces into a cat's mouth. A cat may acquire it by licking its paws after using a shared tray, for example. Bowls or surfaces present a risk if contaminated with faeces; sharing a room does not itself mean airborne spread. A cat without symptoms can also sustain transmission.
Finding infection does not alone show poor household care. Close contact and shared equipment increase exposure in groups even in otherwise well-managed conditions. A new cat or reintroducing an infected cat to the group can bring exposure again.
Risk factors
- kittens and cats under 2 years old;
- cats living in large groups;
- cats with weakened immune defences;
- periods after stress or other intestinal infections.
Young age and group living are key recognised predisposing factors. Less is known about the precise importance of the other listed risks in cats. Trichomonosis does not require immunodeficiency, and older cats can also become infected. Another concurrent intestinal infection can complicate interpretation, but is not present in every patient.
Typical symptoms
- chronic diarrhoea with mucus and sometimes blood;
- foul-smelling, watery or soft stools;
- pain during defecation;
- redness and irritation around the anus;
- normal or slightly reduced appetite, with generally preserved overall condition.
With large intestinal diarrhoea, a cat may repeatedly visit the tray and strain while passing only small amounts. Stool may also leak outside the tray. Anal irritation can cause licking of the rear end. These are possible disease consequences, so punishment for accidents does not resolve the problem.
Many infected cats remain lively and do not lose weight. Substantial weight loss, profuse vomiting or poor general condition may therefore require investigation of another disease alongside trichomonosis. Record stool consistency, defecation frequency, appetite and weight changes. Mention whether other cats have symptoms and which medicines or dietary changes have already been tried.
Complications and consequences
- dehydration with prolonged diarrhoea;
- weight loss;
- chronic intestinal inflammation;
- secondary bacterial infections;
- reduced quality of life.
Severe dehydration or secondary bacterial infection is not an expected consequence of every Tritrichomonas infection. If general condition worsens, the vet assesses additional disease and fluid needs. Ordinary intestinal bacteria found in faeces do not themselves prove a bacterial complication or automatically require antibiotics.
Diagnosis at the vet
- microscopy of fresh faeces to detect flagellated organisms;
- PCR, the most accurate method for detecting T. foetus infection;
- faecal culture, a less sensitive method;
- exclusion of other causes of diarrhoea, including roundworms, Giardia, bacterial infections and IBD.
Routine worm egg testing alone cannot rule out infection. Fresh-sample microscopy looks for moving protozoa but can miss infection. Distinguishing Giardia and other flagellates also requires expertise. T. blagburni culture uses a special growth method rather than ordinary bacterial culture.
PCR detects parasite genetic material and is sensitive, but does not identify every infection either. Sample quality, shedding and previous medicines affect the result. Follow laboratory collection and storage instructions; different tests may need differently handled samples. The vet can also collect a sample directly from the rectum.
A positive result shows infection, but its importance in explaining symptoms is assessed in context. Giardia, for example, may be present at the same time, and one positive result should not explain every later digestive symptom. If suspicion persists despite a negative result, repeat sampling or another method may be needed.
Treatment and follow-up
The vet considers ronidazole for a confirmed infection causing symptoms. It has a narrow safety margin; do not select the amount or product yourself. Ordinary worming medicine or a previous antibiotic course does not replace targeted treatment. Treatment can fail, so continuing symptoms do not mean you should increase the amount yourself.
Ronidazole can cause neurological adverse effects. Before treatment, report other diseases, all medicines and possible pregnancy or nursing. Do not add metronidazole on your own, as combining them can increase adverse effect risk. Follow handling instructions and wear protective gloves when administering it.
Feeding and symptom assessment
Any dietary change is adapted to the cat's situation. There is insufficient research evidence for probiotics or diet as treatment specifically for this infection. Repeated rapid food changes and trials of different products can also make diarrhoea harder to assess. Keep agreed feeding as stable as possible and report if your cat stops eating.
Firmer stools do not confirm parasite elimination. Follow-up testing and timing are chosen separately. If diarrhoea returns, reinfection, treatment failure and other intestinal diseases are considered. Temporary improvement on antibiotics alone does not prove the pathogen has gone.
Household cats and prognosis
Medication of a carrier without symptoms is not automatic. The vet assesses an investigation and treatment plan for the whole group, particularly with recurrence or spread. Separating treated cats from susceptible ones may help, but arrangements also consider stress and the possibility of symptom-free carriers.
Diarrhoea may improve over time even without medication, but this does not mean an affected cat should be left unexamined. Infection can persist after clinical recovery. Monitoring wellbeing, stool quality and infection control is therefore all needed; one good day does not establish lasting recovery.
Prevention
- Maintain good hygiene when keeping cats.
- Disinfect litter trays and bowls regularly.
- Keep kittens and adults separate in breeding establishments.
- Arrange investigation whenever diarrhoea persists.
Remove faeces from trays and clean dirty equipment before disinfection. Use a cat-safe household product according to instructions and allow surfaces to dry. Wash hands after handling faeces and keep cleaning equipment separate from food dishes. Separating kittens and adults alone does not prevent infection if a carrier without symptoms remains in a group.
Feline trichomonosis is not considered a usual infection of people. Good hand hygiene still matters, as other pathogens can occur alongside diarrhoea. Review a new cat's health history and previous diarrhoea before introducing it to the group.
Important for cat owners
Trichomonosis is a common cause of chronic diarrhoea in young cats. Although rarely life-threatening, it clearly affects wellbeing and requires prolonged management. Remember: persistent diarrhoea warrants a veterinary visit, as unsupervised treatment rarely works.
This article provides general information and does not replace veterinary care. If you notice signs of illness in your cat, contact a vet.
Frequently asked questions
Are Tritrichomonas foetus and Tritrichomonas blagburni the same?
Both names are used for feline intestinal infection. T. blagburni is a name now in use, while the older T. foetus still appears in literature and test reports. This is not human trichomoniasis.
Can a faecal sample miss infection?
Yes. Routine parasite testing may not look for this protozoan, and even a targeted test can be negative despite infection. Collection and any repeat tests are agreed with the vet.
Does a cat without symptoms always need medication?
Not automatically. Benefits and risks are assessed alongside the whole household's infection status. However, absence of symptoms does not guarantee a cat cannot spread infection.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Guideline for Trichomonosis, ABCD, accessed 2026-11-03.
- Tritrichomonas in Cats, VCA Animal Hospitals, accessed 2026-11-03.
- Tritrichomonas blagburni, Companion Animal Parasite Council, accessed 2026-11-03.
- Tritrichomonas foetus, University of Liverpool / SAVSNET, accessed 2026-11-03.
- Diarrhoea, Cornell University College of Veterinary Medicine, accessed 2026-11-03.
- Feline enteropathogens and molecular diagnostics: benefits, limitations and clinical applications, Journal of Feline Medicine and Surgery, accessed 2026-11-03.
- Guideline for Giardiasis, ABCD, accessed 2026-11-03.