Analysis of the phenotypes in field populations ofEimeria acervulinaexpressing dual drug‐resistance to decoquinate and clopidol

Abstract

Two strains of Eimeria acervulina were derived from samples collected from broiler houses where chicken flocks were being medicated with decoquinate (a quinolone); previous flocks in the same houses had been medicated with clopidol (a pyridone). The strains were found to be resistant to both drugs. In the laboratory, a dichotomous series of selection passages through chicks medicated with decoquinate or clopidol was used to demonstrate that both the original field populations of E, acervulina included at least some parasites that expressed simultaneous resistance to both drugs, rather than comprising subpopulations that were each resistant only to one drug or the other. This is the first time that a phenotypic analysis of the individuals in an eimerian population has been carried out. The relevance of this finding to the efficacy of Lerbek, a synergistic mixture of clopidol and methyl benzoquate (another quinolone), originally introduced in an attempt to delay the emergence of drug-resistant coccidia, is discussed. It is concluded that Lerbek would have been completely effective if resistance to neither of its components had already emerged before Lerbek was launched; some efficacy would also have been retained if resistance to only one of its components had already developed. However, if resistance to both components had already developed, the dual resistance of some individual parasites would have rendered Lerbek less effective than if all parasites were resistant only to one or the other of its components.

Focused review: The role of drug combinations for the control of coccidiosis in commercially reared chickens

“…Most broiler isolates had acquired resistance to methyl benzoquate and clopidol prior to the introduction of Lerbek hence the failure of the combination to control these strains. Lerbek would have been effective if resistance to its components had not emerged prior to its introduction, but unfortunately this was not the case ( Williams, 1998 ). However, an investigation of the sensitivity of Eimeria species from Belgian broiler farms indicated a 50% improvement in weight gain, feed conversion and oocyst production compared with infected controls in birds given Lerbek ( Peeters et al, 1994 ).…”

Chemical and Pharmacological Properties of Decoquinate: A Review of Its Pharmaceutical Potential and Future Perspectives

“…In the case of cytochrome bc 1 inhibitors, new antimicrobial agents are being explored primarily with this goal in mind [ 66 , 67 ]. DQ, for example, has already been described as a drug that exhibits cross-resistance, i.e., the ability of coccidia to survive the anticoccidial effects of a drug to which they have never been exposed because they have already developed resistance to a chemical agent [ 73 ]. Options that have been explored in recent years to combat drug resistance include nanosystems [ 68 ].…”

A laboratory method for the single‐passage selection of drug‐resistant mutants from populations ofEimeriaspecies in chickens and its potential value in the choice of field use concentrations for new anticoccidial drugs

“…It may have been inferred from these facts, had they been known before decoquinate was marketed, that a use concentration of 0.004% w/w would have produced drug resistance to E. tenella in the field extremely rapidly. In fact, this proved to be the case, and coccidial resistance developed within a few months, often during the first broiler crop on a farm to be medicated with a quinolone (Ryley, 1980;McDougald, 1982;Williams, 1998). Doubtless, the phenomenon of absolute resistance to quinolones exacerbated the problem.…”