Tritrichomonas PCR (feline trichomoniasis) in cats and dogs
Tritrichomonas is a single-celled parasite of the cat’s large intestine that can cause long-lasting diarrhoea, most often in young cats from catteries and multi-cat households. Forms may still call it Tritrichomonas foetus; the feline parasite has since been renamed T. blagburni. PCR on a stool sample is the test of choice.
What it shows
PCR looks for the parasite’s DNA in faeces. It is the preferred test because the other methods are less sensitive:
- Direct wet mount — fresh faeces, examined within hours, are searched under the microscope for moving pear-shaped organisms. Sensitivity is low, and the parasite is often mistaken for Giardia, which moves differently.
- Culture — faeces are placed in a special medium, for example a commercial pouch system, so the organisms multiply. The result can take one to two weeks.
- PCR — also helps tell T. blagburni apart from Pentatrichomonas hominis, another trichomonad that looks similar under the microscope.
How the sample is taken matters. Ideally faeces are collected with a rectal or faecal loop; colonic flushing is used less often. In a laboratory series of 1717 cats, loop samples were positive more often (23%) than naturally passed faeces (15%) or flush samples (14%), although the study could not prove the technique was the reason.
Higher than reference — what it may be a sign of
- Detected — the parasite’s DNA is in the stool. In a cat with long-lasting large-bowel diarrhoea this supports trichomoniasis; the vet reads it together with the signs and other stool tests.
- Detected in a cat without signs — many cats are carriers with no signs even though they test positive by PCR, so a positive result alone does not mean the parasite explains every bout of diarrhoea.
- Typical picture — frequent foul-smelling diarrhoea, often semi-formed, with mucus or fresh blood. It can last weeks, months or years and often comes and goes.
Lower than reference
“Not detected” lowers the likelihood but does not exclude infection: shedding can be intermittent, which leads to false-negative results, and the way the sample was taken affects the result. Some cats with a negative result continue to have diarrhoea; other causes, including co-infections such as Giardia or Cryptosporidium, are then considered. The vet may repeat the test on a new sample.
Look at together with
- Giardia — easy to confuse with Tritrichomonas under the microscope, and the two can occur in the same cat.
- Cryptosporidium — another possible co-infection in cats with chronic diarrhoea.
- Where the cat comes from — a cattery or a multi-cat household makes the parasite more likely.
Units and conversion
Results have no unit. PCR is reported as detected or not detected (sometimes positive or negative). Wet mount and culture are reported as organisms seen or not seen. In the app these results are stored as text.
Reference range
The reference range is on your lab’s form; for this test the expected result in a healthy cat is not detected. A positive PCR shows the parasite is present in the large intestine. Whether it explains the diarrhoea, the vet decides together with the signs, the cat’s history and other stool tests.
Cats and dogs
Infection and disease are most common in cattery cats; age at onset ranges from birth to 24 months, averaging 9 months. In the large PCR series, positives were less common in domestic non-pedigree cats and more common in Abyssinians. Infection of the urinary and genital tract is very rare, and the parasite is not considered zoonotic. Self-resolution is more likely in households with fewer cats.
The feline parasite is rarely found in dogs. When trichomonads are seen in a dog’s faeces, they are usually Pentatrichomonas hominis, and PCR helps tell them apart. A test for this parasite in a dog is unusual and is ordered by the vet for a specific reason.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- CAPC (Companion Animal Parasite Council) — Trichomoniasis guidelines
- ABCD (European Advisory Board on Cat Diseases) — Tritrichomonas infection in cats, fact sheet (2025)
- ESCCAP Guideline 06 (3rd edition, 2025) — Control of intestinal protozoa in dogs and cats
- Hedgespeth et al., J Vet Intern Med 2020 — Fecal sample collection technique and Tritrichomonas foetus PCR results in 1717 cats
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.