Update on Feline Trichomonosis: To Treat or Not to Treat?

Tritrichomonas foetus is a protozoan parasite that can cause chronic, waxing and waning diarrhea in cats. The organism was identified over 20 years ago as a potential cause of feline diarrhea, but according to a review article in The Journal of Feline Medicine and Surgery, important questions about T. foetus infection remain—including whether or not to treat it.

T. foetus inhabits the cecum and colon of infected cats and is shed in feces. Transmission to other cats is through the fecal—oral route. Diarrhea associated with T. foetus can be semi-soft but may be mucoid or bloody and is usually not accompanied by other signs (eg, weight loss). Although the diarrhea can recur intermittently for years, it can also resolve on its own.

Diagnosis

The authors caution that diagnosis of T. foetus is tricky. Because the organism is fragile, only fresh fecal samples (ideally obtained while in the veterinary office) are likely to be diagnostic. Further, the sample should be obtained while the cat is having diarrhea, as formed fecal samples are less likely to harbor the parasite.

According to the authors, regular fecal flotation or centrifugation won’t detect T. foetus. Direct examination of a fecal wet mount under a microscope may reveal the organism, but this technique is only 14% sensitive. Additionally, T. foetus is easily misdiagnosed as Giardia, further limiting the reliability of this method. The authors note, “it is always worth performing a fecal wet mount examination because it might yield an easy diagnosis. However, due to low sensitivity, a negative wet mount examination cannot be relied upon to rule out trichomonosis.”

Fecal culture testing and histopathologic examination of tissue samples are more diagnostically reliable than fecal wet mounts, but the authors’ preferred diagnostic method is polymerase chain reaction (PCR) testing of diarrheic fecal material, as this appears to be the most sensitive method available.

Treatment and Prognosis

The only medication shown to have efficacy against T. foetus is ronidazole. However, ronidazole has a relatively narrow safety margin in cats, so careful dosing is required to reduce the risk for adverse effects associated with neurotoxicity (including ataxia and seizures). The authors also recommend using PCR to retest cats after treatment, but they caution that asymptomatic infection is common and resolution of the diarrhea makes PCR testing less likely to identify infection in cases of treatment failure.

According to the authors, ronidazole is currently believed to be effective in 60% of infected cats, but these numbers may be inaccurate because studies that used wet mount preparations for follow-up testing may have reported false-negative results due to their diagnostic methods.

Perhaps the biggest question regarding treatment is whether it is necessary for infected cats. The authors commented that an estimated 88% of infected cats experience spontaneous resolution of their diarrhea within 2 years, although these cats may remain PCR positive. When one considers the potential for ronidazole-associated toxicity, it may seem prudent to consider not treating positive cats at all.

The authors point out that resolution of diarrhea does not indicate that the infection has been cured, noting that “most of these cats will remain infected based on positive PCR test results for Trichomonas species. This suggests that cats do not develop an effective immune response to Tritrichomonas species infection and are incapable of eliminating the parasite.”

So, of all the active research pursuits concerning T. foetus, the question of whether “to treat or not to treat” may still be one of the most compelling.