Development of Experimental Cystoisospora canis Infection Models in Beagle Puppies and Efficacy Evaluation of 5 % Ponazuril (Toltrazuril sulfone) Oral Suspension

In a pilot study, three pairs of Beagle puppies were inoculated with 2.5, 3.75 or 5 x 104 sporulated oocysts of Cystoisospora canis. All exhibited patent infections within ten days post-inoculation. In an efficacy study, 33 puppies were given 5 x 104 oocysts of C. canis and randomly allocated to receive 20, 30, 40, or 50 mg/kg ponazuril on day 0, or 30 mg/kg ponazuril or placebo on days 0 and 7. Clinical health observations and oocyst excretion were monitored daily post treatment. All dosages decreased oocyst counts > 97 % (P < 0.05) by day 4. In an attempt to prolong patency, 42 puppies were inoculated with 1 x 104 oocysts on days –10, –8 and –6. Puppies were allocated to receive 30 or 50 mg/kg ponazuril on day 0, or 30 mg/kg ponazuril or placebo on days 0 and 7. All dosages decreased oocyst counts (P < 0.05) by day 2. Analyses indicated that greater oocyst count reduction was achieved by higher dosages of ponazuril and by a second dose on day 7. The frequency of abnormal clinical signs did not differ significantly between treatment groups in either study, and no adverse effects were associated with any dosages of ponazuril.