Efficacy of a low-dose praziquantel and fenbendazole protocol in the treatment of asymptomatic schistosomiasis in dogs.

Background: Established treatment protocols for schistosomiasis (Heterobilharzia americana) in dogs are expensive. Anecdotal reports suggest that lower doses of praziquantel, combined with fenbendazole, may eliminate asymptomatic infections.

Objectives: Evaluate the efficacy of a low-dose praziquantel and fenbendazole protocol to manage asymptomatic schistosomiasis in dogs and compare fecal saline sedimentation (FSS) and fecal PCR (FPCR) for therapeutic monitoring.

Animals: Twelve asymptomatic dogs with positive FPCR and FSS results for schistosomiasis.

Methods: Prospective observational study. On day 0, dogs received praziquantel at a median dose of 5 mg/kg PO q8h for 2 days, with fenbendazole at 24 mg/kg PO q24h for 7 days. Fecal PCR and FSS were repeated in all dogs on days 30, 60, and 90.

Results: By day 30, 10 of 12 dogs were negative by FSS, but only 3 of 12 were negative by FPCR. By day 60, all 12 dogs were negative by FSS, and 8 of 12 had become negative by FPCR. By day 90, all 12 dogs remained negative by FSS, but 5 of 12 were positive by FPCR (including 2 that were negative by FPCR on day 60). Three dogs that were positive by FPCR on day 60 were re-treated and subsequently became both FPCR and FSS negative. One FPCR-positive dog developed a mild increase in serum ALP activity, another developed mild hypercalcemia, and a third developed diarrhea.

Conclusions And Clinical Importance: A low-dose praziquantel/fenbendazole protocol may be effective for asymptomatic schistosomiasis in some dogs, but monitoring to ensure treatment success is recommended. Fecal saline sedimentation and FPCR may demonstrate discrepant results, with FPCR being positive more frequently.