Multiple anthelmintic drug resistant Ancylostoma caninum in foxhounds.

Ancylostoma caninum is the most common and important gastrointestinal nematode of dogs in the United States. Despite recent reports of A. caninum isolates resistant to all classes of anthelmintics, little is known about the frequency and extent of this anthelmintic resistance. The study aim was to evaluate the efficacy of three commercial anthelmintic products in the treatment of foxhound dogs with a history of persistent A. caninum infections. In the first phase of this study, 35 foxhounds were randomly divided into three treatment groups: moxidectin/imidacloprid (MI), pyrantel pamoate/febantel/praziquantel (PFP), and emodepside/praziquantel (EP). Fecal samples were collected on day 0, 11, and 33 post-treatment (PT), and hookworm eggs were quantified using the mini-FLOTAC technique with a multiplication factor of 5 eggs per gram (EPG). The fecal egg count reduction (FECR) on day 11 PT was 65% (95% CI: 62%-68%) for MI, 69% (95% CI: 66%-72%) for PFP, and 96% (95% CI: 94%-97%) for EP. On day 33 PT, the FEC in the MI and PFP groups returned to almost the same values as on day 0, while in the EP group, the FEC remained low. Since MI and PFP proved ineffective, 32 animals were randomly divided into two groups in the second phase. They were treated either with a combination of MI/PFP or EP. The FECR at day 13 PT for the combination MI/PFP was 89% (95% CI: 87%-91%) and 99% (95% CI: 98%-99%) for EP. These results suggest that this A. caninum population is resistant to multiple anthelmintics. Although the combination of MI/PFP improved the anthelmintic efficacy, the FECR remained below 90%. Future studies are indicated to evaluate further the epidemiology of persistent hookworm infections in dogs in the US and to identify more effective treatment protocols as they pose a significant health risk to canine and human health.