Investigating the Impact of Anthelmintic Resistance in Nematode Parasites of Poultry

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Institution: University of Georgia

Principal Investigator:
Dr. Ray M. Kaplan
College of Veterinary Medicine
Department of Infectious Diseases
501 DW Brooks Dr.
Athens, GA 30602

An important factor in the profitable production of poultry is the management of helminth parasites. Ascaridia galli and Ascaridia dissimilis are nematodes of the Ascarididae family and are two of the most common and economically important nematode parasites of chickens and turkeys, respectively, with up to 100% of birds in some flocks infected. Helminth control is typically achieved via the frequent administration of anthelmintic drugs, with fenbendazole (FBZ) being the most commonly used drug. Fenbendazole is currently the only FDA approved anthelminthic for use within the poultry industry. Researchers have recently completed a study in turkeys that definitively demonstrated resistance to FBZ in A. dissimilis, which has led to further investigations.

In this study, the researchers had three primary objectives: (1) Measure the production impact of drug-resistant A. dissimilis on turkeys in a production-like setting, (2) Develop a molecular diagnostic test to detect and measure resistance in A. dissimilis using a next generation deep sequencing approach, and (3) Measure the efficacy of fenbendazole against a suspected resistant isolate of Heterakis gallinarum.

To address the first objective, production parameters, such as feed conversion, weight gain and worm counts, were measured in turkeys infected with either a drug-susceptible or drug-resistant strain of A. dissimilis and either treated or not treated with FBZ. Data showed birds infected with resistant parasites and treated with FBZ had significantly poorer feed conversion when compared to those infected with susceptible parasites and treated. Also, as might be expected, birds infected with susceptible parasites and treated with FBZ had significantly better feed conversion than infected birds that were left untreated. Together, these results highlight the impact parasites may have on feed conversion in poultry and the costs associated with failure to clear resistant parasites. Fenbendazole-resistant A. dissimilis has the potential to impart substantial economic losses in the production of commercial turkeys.

Objective two was unable to be accomplished. A molecular diagnostic could not be developed as analyses of sequence data from resistant parasites failed to show any known resistance-associated variants in the beta-tubulin genes. It appeared that resistance in ascarids did not involve the typical mutations in the beta-tubulin gene. Further, genomic work and mapping studies will be needed to determine the underlying mutations associated with Benzimidazole resistance in ascarids. However, once resistance-associated mutations can be identified, the proposed diagnostic can likely be developed in a future study.

Experiments conducted for objective three revealed that neither the label dose of FBZ, nor a dosage twice that of the label dose, significantly reduced parasite burdens, indicating that the isolate was highly resistant to FBZ. These results raise significant concerns for Blackhead control, as vector control is currently one of the few options available.

Overall, results demonstrate the significant impact that nematode parasites may have on the health and productivity of poultry and highlights the need for new control strategies for continued efficiency in production. The lack of known resistance-associated mutations in FBZ-resistant nematodes is entirely novel and presents an important new avenue of study for all ascarids.

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