Feline trichomonosis — what to test, what was dosed, what to watch
Tritrichomonas foetus, also proposed as Tritrichomonas blagburni — the same organism, and both names appear on laboratory reports. Compiled from the sources at the foot. This is not a protocol and it does not recommend a dose: it summarizes published evidence so the decision stays with the veterinarian examining the cat.
1 · Patient
2 · The test to request
- PCR for Tritrichomonas on feces, collected by fecal loop while the cat is passing loose stool — fresh, free of litter, which inhibits the reaction. In 1,717 cats, loop samples were 2.04× more likely to be PCR-positive than colonic flush, and the earlier preference for flushing rested, by the authors' later account, on anecdote.
- Sensitivity is about 94%. A negative reduces the probability but does not exclude it, and a direct smear (≈14%) cannot exclude it at all. Consider Giardia and Cryptosporidium alongside.
- Antibacterial withdrawal is unsettled. ABCD advises stopping oral antibacterials about seven days before sampling; the 1,717-cat dataset found no association between prior antibiotic, antiparasitic, anticoccidial or corticosteroid treatment and a positive PCR. Both positions are published, neither has been shown to be correct.
3 · The published dosing history, because it reversed
| Year | Published recommendation | Basis |
|---|---|---|
| 2006 | 30–50 mg/kg PO q12h × 14 d | Cleared 10 of 10 experimentally infected cats, PCR-negative 21–30 weeks later; 10 mg/kg failed in all. |
| 2011 | — | PK: oral absorption ≈99.6%, t½ ≈10.5 h, detectable at 48 h. Twice-daily dosing predicted to accumulate. |
| 2013 | 30 mg/kg q24h, delayed-release guar gum | 84% clearance, no adverse events. Not commercially available or readily compoundable. |
| 2014 | 30 mg/kg PO q24h × 14 d; q12h withdrawn | Letter from the original authors, citing accumulation and neurological toxicity risk. |
The 2014 letter stated that the revised once-daily regimen had never been tested for efficacy: it followed from pharmacokinetics, not a treatment trial, and that work still appears outstanding. Ronidazole is not approved for any companion animal and is supplied compounded — capsules, solutions and medicated treats may not be bioequivalent, and the 10% pigeon powder is named in the literature as a cause of apparent failure.
4 · Monitoring — signs that mean stop, not finish
Tremor · ataxia · head tremor · agitation · nystagmus · hyperesthesia · seizures
Neurological signs typically begin at least three days into treatment and usually resolve one to four weeks after the drug is stopped. Continuing after signs appear is what turns a reversible toxicity into a serious one. Many cats that reach this point have already received enough drug to have cleared the infection, which is why retesting afterwards matters. Ronidazole is considered contraindicated in pregnant or lactating queens, and kittens under twelve weeks are usually dosed lower because of immature metabolism.
Handler exposure: ronidazole is a suspected human reproductive and carcinogenic hazard — the reason for the food-animal ban, not a precaution invented for cats. Compounded powder is the highest-exposure form; pregnant, breastfeeding and immunocompromised people should not handle it.
5 · Retest, and what a negative does and does not mean
- No agreed interval exists. Relapse has been documented as late as 20 weeks after the last dose, so a four-week negative is an early reading, not a result.
- A negative is a point-in-time result on an assay of roughly 94% sensitivity, on a specified sample type. Record sample method, laboratory and date, or the result cannot be interpreted later.
- Three states, not two: carrier (positive, with or without diarrhea — shedding, can infect others) · suppressed (signs resolved, no valid retest — unknown, and where most treated cats are discharged) · cleared on retest (negative on a properly collected sample, late enough to mean it).
- Diarrhea usually resolves on its own within about two years in untreated cats, and treated cats in that cohort took longer; the infection persists in most untreated cats.
6 · If treatment fails, work the differential in this order
Confirm failure by testing rather than by persistence of diarrhea: some cats with recurrent diarrhea no longer carry the organism. Then work the differential in order: formulation (compounded product, capsule versus liquid, pigeon powder) → dose and compliance (weight measured, not estimated) → reinfection from an untreated in-contact cat → resistance (documented, rare but real). In the authors' experience, escalating dose or duration in a genuinely resistant cat does not eradicate and increases toxicity risk. Roughly one in four treated cats remained positive on repeat testing.
Sources
- Foster DM, Gookin JL, Poore MF, et al. Outcome of cats with diarrhea and T. foetus infection. J Am Vet Med Assoc 2004;225:888–892.
- Gookin JL, Copple CN, Papich MG, et al. Efficacy of ronidazole for treatment of feline T. foetus infection. J Vet Intern Med 2006;20:536–543.
- Gookin JL, Stauffer SH, Dybas D, Cannon DH. In vivo and in vitro aerobic resistance of feline T. foetus isolates to ronidazole. J Vet Intern Med 2010;24:1003–1007.
- LeVine DN, Papich MG, Gookin JL, et al. Ronidazole pharmacokinetics after intravenous and oral immediate-release capsule administration in healthy cats. J Feline Med Surg 2011;13:244–250.
- Papich MG, LeVine DN, Gookin JL, et al. Ronidazole pharmacokinetics following delivery of a delayed-release guar gum formulation. J Vet Pharmacol Ther 2013;36:399–407.
- LeVine DN, Gookin JL, Papich MG, Davidson GS. Twice-daily dosing of RDZ no longer recommended (letter). J Feline Med Surg 2014;16:198.
- Gookin JL, Hanrahan K, Levy MG. The conundrum of feline trichomonosis. J Feline Med Surg 2017;19:261–274.
- Hedgespeth BA, Stauffer SH, Gookin JL. Fecal sample collection technique and treatment history with T. foetus PCR results in 1,717 cats. J Vet Intern Med 2020;34:734–741.
- ABCD. Guideline for trichomonosis. abcdcatsvets.org — antibacterial withdrawal, treatment options.
tritrichomonasproject.org/print/for-your-vet