Review identifies challenges of trichomonosis infections in cats

A recent review of trichomonosis in cats investigates what has been learned about it and the complications and frustrations that still persist.

The parasite Tritrichomonas foetus lives in the feline large intestine and is a common cause of colitis in cats. Researchers from North Carolina State University, while looking at studies that have advanced our understanding of trichomonosis, also consider what questions remain and the need for new treatments for the infection. The review was published in the March issue of the Journal of Feline Medicine and Surgery.

Trichomonosis infections are widespread in cats and present a puzzle, as the diarrhea can be treated, but the infection can persist for years after the symptoms are treated. The duration of the diarrhea can last anywhere from one day to eight years and is typically of a “cow pie” consistency. In most cases, the cats maintain good health, normal appetite, and body condition. Cats from catteries or shelters seem to be at an increased risk for infection.

Advances have been made in developing diagnostic tests for the infection. The review provides three methods of collecting samples to test, but they recommend that the one with the most success consists of “passing a red rubber catheter into the proximal colon for the instillation and recovery of several milliliters of sterile saline.” Any samples collected should be left unrefrigerated, as refrigeration kills the Tritrichomonas species. Furthermore, non-diarrheic and dry stool should not be used as they rarely result in positive test results, even if the cat is infected.

The only drug currently demonstrated to be effective in eliminating trichomonosis in cats is ronidazole (RDZ), a drug with a narrow safety margin and increasingly recognized clinical resistance. RDZ has not been approved by the FDA for human or veterinary use and is banned from use in food animals because of the potential hazard to people. Owners of cats who will be treated by RDZ will need to give informed consent and monitor cats closely for signs of toxicity.

Researchers estimate that 60% of cats treated with RDZ will have close to complete resolution of clinical signs of trichomonosis, but sometimes this means the infection is suppressed rather than eradicated completely. Some cats will continue to have diarrhea and an infection, other cats might have recurrent diarrhea but no longer have an infection. In cases of cats that are still infected, the case might be that they need a higher dose of RDZ, that they have been exposed to another cat with trichomonosis, or that their strain of infection is resistant to RDZ.

Based on the toxicity of RDZ, some question whether trichomonosis should be treated at all. If left untreated “it is estimated that most cats (88%) with Tritrichomonas species infection will undergo spontaneous resolution of their diarrhea within 2 years.” However, most of the cats will still test positive for the infection.

The researchers conclude that more questions can still be answered about Tritrichomonas including whether alternate diagnostic approaches can provide more sensitive detection, how the Tritrichomonas species causes diarrhea, whether safer and more effective drugs can be identified for treatment, and what the long-term effect of infection has on feline gastrointestinal health.

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