Anticoccidial drug resistance in the southeastern United States: polyether, ionophorous drugs

Area of Science:

• Veterinary Parasitology
• Antiparasitic Drug Efficacy
• Poultry Health

Background:

• Coccidiosis remains a significant threat to poultry production worldwide.
• Ionophore anticoccidials are widely used for disease prevention in poultry.
• Emerging drug resistance in Eimeria species necessitates ongoing monitoring of drug sensitivity.

Purpose of the Study:

• To assess the sensitivity of coccidia isolates from U.S. poultry farms to ionophore anticoccidial drugs.
• To compare the efficacy of different ionophore drugs against various coccidia isolates.
• To evaluate the impact of testing methodologies on resistance determination.

Main Methods:

• Isolation and characterization of 52 coccidia isolates (24 pure, 28 mixed species) from U.S. poultry farms.
• In vitro sensitivity testing of isolates against individual and grouped polyether, ionophorous drugs.
• Evaluation of drug efficacy using lesion score reduction and bird weight gain as primary endpoints.

Main Results:

• All isolates showed some response to ionophores; none were completely resistant.
• Salinomycin (64% control) and lasalocid (56% control) were most effective based on lesion scores.
• Lasalocid (97% control) and salinomycin (90% control) showed superior efficacy based on weight gain.
• Significant differences in isolate response to drugs and drug groups were observed.
• Testing methodology, specifically the chosen endpoint, influenced the designation of resistant or sensitive isolates.

Conclusions:

• Poultry coccidia isolates exhibit variable sensitivity to ionophore anticoccidials.
• Salinomycin and lasalocid represent effective options for coccidiosis control, with differing strengths depending on the efficacy metric.
• The selection of endpoints in drug sensitivity testing is critical and can impact resistance classification.