Efficacy of ronidazole for treatment of feline Tritrichomonas foetus infection

Objectives: To determine the efficacy of ronidazole (RDZ), tinidazole (TDZ), and metronidazole (MDZ) against Tritrichomonas foetus in vitro and of RDZ for treatment of feline naturally occurring or experimentally induced T foetus infection. Animals: A cat naturally infected with T foetus infection and diarrhea. Ten specific-pathogen-free (SPF) kittens. Procedure: RDZ, TDZ, and MDZ were tested for activity against 3 different feline isolates of T foetus in vitro. RDZ then was administered to a naturally infected cat at 10 mg/kg PO q24h for 10 days. SPF kittens were infected orogastrically with feline T foetus and treated with either placebo or RDZ (10 mg/kg PO q12h for 14 days). Cats with relapsing infection or those receiving placebo were treated subsequently with RDZ (either 30 or 50 mg/kg PO q12h for 14 days). Feces were examined for T foetus by direct microscopy, culture, and polymerase chain reaction (PCR) testing weekly. Results: Both RDZ and TDZ killed T foetus at concentrations > 0.1 mu g/mL in vitro. In the naturally infected cat, RDZ abolished diarrhea and T foetus infection for 85 days after treatment, at which time infection and diarrhea relapsed. Retreatment with RDZ eradicated diarrhea and T foetus infection for over 407 days. In experimentally induced infection, RDZ at 10 mg/kg caused initial improvement, but infection relapsed in all 5 cats 2 to 20 weeks after treatment. At 30 or 50 mg/kg, 10/10 cats were negative for T foetus infection for follow-up durations of 21 to 30 weeks after treatment. Conclusions and Clinical Relevance: Oral administration of RDZ at 30 to 50 mg/kg q12h for 14 days resolved diarrhea and eradicated infection (on the basis of polymerase chain reaction [PCR] testing) in I naturally infected cat and 10 experimentally inoculated cats receiving a different isolate of T foetus.