QPCR for the detection of Tritrichomonas foetus in cats
The protozoal parasite Tritrichomonas foetus (TF) is now well recognised as a cause of chronic diarrhoea in cats. It is a particular problem in multi-cat households, notably pedigree breeding catteries and rescue shelters, where one or more cats within the group are usually affected. TF-associated diarrhoea is most often seen in cats under 1 year of age, but it has also been reported in older cats. The parasite targets the large bowel causing colitis, with frequent passage of small quantities of liquid to semi-formed faeces often with blood, mucus and straining. Some affected cats develop faecal incontinence.
The motile TF trophozoites can be identified in fresh faeces (ideally <2 hours old) by direct microscopic examination, but the sensitivity of this method is very low. Infection can also be diagnosed by culturing the organism using the commercially available InPouch™ TF kit, which has been marketed for the diagnosis of TF infection in cattle. However, the InPouch™ method is laborious and time consuming since pouch contents need to be examined daily by microscopy and results can only be considered negative after 12 days. Additionally the specificity of the InPouch™ system is unknown as a positive result does not preclude the possibility of infection with trichomonads other than TF. More recently faecal PCR has been recommended as the diagnostic test of choice for TF infection, being more sensitive than both direct examination and culture by the InPouch™ method. However, PCR on faeces can be problematic due to the PCR-inhibitory effect of many substances that are co-purified with the DNA during extraction.
A real-time quantitative (Q)PCR has recently been developed by the Molecular Diagnostic Unit, Langford Veterinary Services for the detection and quantification of TF in faecal samples. This new multiplex assay is the first to use an internal amplification control PCR alongside the TF PCR, enabling detection of any inhibitory substances present in the extracted DNA, which could cause false negative TF results. The use of QPCR in this new assay also allows us to report the relative amount of TF present in the faeces, which may be useful in monitoring the response to treatment.
The treatment of choice appears to be ronidazole, which is related to metronidazole and is used to treat tritrichomoniasis in pigeons. It is not licensed for cats and experience of its use is currently limited, although it appears to be effective. A dosage of 30 mg/kg orally once daily for two weeks has been suggested. Infrequent cases of neurotoxicosis have been reported with drug administration and it is teratogenic so must be handled with care. Consultation with a feline specialist is advised before embarking on treatment.
The diarrhoea will usually resolve spontaneously in untreated cats although this may take some time; months or more. Cats in which clinical signs (diarrhoea) have resolved seem to continue to excrete the organism for periods of up to two years.
New sample submission information
The sample required for the Tritrichomonas foetus QPCR is a small volume (2-5ml) of fresh faeces. Please ensure that no cat litter is present. Samples should be kept refrigerated and sent directly to our laboratory.
Further information
- New QPCR test now available for vets to investigate cats with diarrhoea caused by Tritrichomonas foetus
- More information about Tritrichomonas foetus can be found on the Feline Advisory Bureau website.