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Drug resistance in coccidia: a robenidine-resistant strain of eimeria tenella
Abstract:
Tests for resistance to a recently introduced anticoccidial drug, robenidine, were performed on a strain of Eimeria tenella recovered from broiler chickens infected with acute cecal coccidiosis. The strain was identified previously and again confirmed by the timing of mortality of the infected chickens (five to six days postinfection), the appearance of lesions and parasites in ceca only, and the measurements (21.6 +/- 1.9 micron X 19.8 +/- 2.4 micron) of the oocysts. The tests showed that the strain of E. tenella could establish infections in chickens medicated with fourfold the recommended level of robenidine in feed but no oocysts could be recovered from the feces of infected chickens when the level of drug was increased to eightfold. The decrease in mortality, in the severity of lesions and oocyst output and the increase in the average weight gain of infected chickens followed closely the increase in the level of robenidine in feed. In contrast, no infections were found in chickens infected with a sensitive strain of E. tenella and maintained on feed mixed with the recommended level of robenidine. This and other findings discussed here show that resistance to robenidine is developing in coccidia commonly found in broiler houses.
Insights
Resistance to the anticoccidial drug robenidine is emerging in Eimeria tenella strains affecting broiler chickens. Higher drug levels reduced infection severity, but indicate developing resistance in field populations.
Area of Science:
- Veterinary Parasitology
- Poultry Health
- Antiparasitic Drug Resistance
Background:
- Coccidiosis, caused by Eimeria species, is a significant disease in broiler chickens.
- Robenidine is a recently introduced anticoccidial drug used to control coccidiosis.
- Monitoring drug resistance is crucial for maintaining effective disease control strategies.
Purpose of the Study:
- To assess the resistance of a field strain of Eimeria tenella to the anticoccidial drug robenidine.
- To determine the efficacy of increasing robenidine dosages against a resistant Eimeria tenella strain.
- To evaluate the potential for robenidine resistance development in broiler farm coccidia populations.
Main Methods:
- Isolation and identification of an Eimeria tenella strain from infected broiler chickens.
- Experimental infection of chickens with the E. tenella strain at varying robenidine feed concentrations (fourfold and eightfold recommended levels).
- Monitoring of clinical signs (mortality, lesions), parasite oocyst shedding, and chicken weight gain.
Main Results:
- The Eimeria tenella strain established infections at fourfold the recommended robenidine level.
- No oocysts were recovered at eightfold the recommended robenidine level, indicating partial resistance.
- Increasing robenidine dosage reduced mortality, lesion severity, and oocyst output while improving weight gain.
Conclusions:
- The tested Eimeria tenella strain exhibits resistance to robenidine at standard therapeutic levels.
- Robenidine efficacy is dose-dependent, with higher concentrations mitigating infection.
- Developing resistance to robenidine in field strains of Eimeria poses a significant threat to coccidiosis control in commercial broiler production.