A small-scale survey of fenbendazole resistance in Ascaridia galli and Heterakis gallinarum, two common ascarid parasites of poultry

Resistance to benzimidazole (BZ) anthelmintics is a widespread problem in parasitic nematodes that infect production animals such as sheep and goats, and an emerging issue in ascarid parasites of poultry. Ascarid parasites are highly prevalent across commercial poultry species and are associated with significant production losses. The BZ drug fenbendazole (FBZ) is the only approved treatment for ascarid infections in poultry, and previously, FBZ resistance has been identified in Ascaridia dissimilis, the large ascarid of turkeys, and Heterakis gallinarum, the cecal ascarid. Here, we have conducted a small-scale survey of the prevalence of resistance by screening FBZ efficacy against thirteen isolates of Ascaridia galli and eight isolates of H. gallinarum. Four weeks after initial infection, treated animals received FBZ (SafeGuard Aquasol) for five days, per the manufacturer's directions. One week post-treatment, animals were necropsied for parasite quantification to determine treatment efficacy. A single isolate of A. galli and all of the isolates of H. gallinarum were found to be resistant. This finding demonstrates that resistance has emerged in all three major species of poultry ascarid and is potentially common in H. gallinarum, highlighting that resistance is a major problem to be considered. Poultry production lacks other approved options for mitigating ascarid infections, and as resistance increases in prevalence, production loss associated with infections will continue to increase, impacting the economics of the industry. The current study uses sampling and screening of parasites. Methods for larger-scale screenings are necessary to understand the full scope of resistance within poultry production, necessitating partnerships with production operations and country-wide sampling efforts. However, from our survey, it is clear that stakeholders should be aware of the concerns associated with resistance, and that the industry should consider the development of new treatments and management strategies for parasite control.