Chemotherapy of Chicken Coccidiosis

Populations of Eimeria species in chickens frequently include mutants that are resistant to an anticoccidial drug without having been previously exposed to it. Such mutants are described here as 'inherently resistant'. A novel laboratory method of selecting them from their parent populations is described. Selection may be achieved in a single in vivo passage in chickens. Decoquinate-resistant mutants were selected from a previously unexposed E. tenella strain: they tolerated > 0.625% w/w decoquinate in the food of chicks, whilst the rest of the population was sensitive to < 0.002% w/w. This single-passage method has a unique advantage over others; development of resistance to different drugs may be validly compared by using a single criterion, the lowest selective concentration (LSC), all other experimental factors remaining constant. Furthermore, the method is economical with time, facilities and experimental animals, and may have a predictive value in the choice of use concentrations for new anticoccidial agents. A potential selection index (PSI), the proposed or actual field use concentration of a drug divided by its LSC, is defined. It is suggested that a field use concentration for a new drug should be somewhat lower than the LSC, and the overall PSI for all Eimeria species and strains tested should therefore be < 1. In the present study, the PSI for decoquinate and E. tenella was 8.00, which is consistent with the very rapid development of resistance to quinolones that occurred in the field.

Section: Demonstration Of Single-passage Selection Of Drugresistant Mmentioning

confidence: 69%

Section: Demonstration Of Single-passage Selection Of Drugresistant Mmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Williams¹

1998

“…Monensin, arprinocid and robenidine were used. The drugs were included in a standard diet containing vitamin K formulated by the Coccidiosis Discussion Group (Ryley and Betts, 1973) at the following concentrations: monensin 40, 50,60 or 100 ppm; arprinocid 20 or 50 ppm; robenidine 60 ppm; each treatment group comprised two sub-groups of 28-30 chickens. The medicated food was fed from one-day-old to approximately 10 weeks of age.…”

Section: Laboratory Trialmentioning

confidence: 99%

The effect of some anticoccidial drugs on the development of immunity to coccidiosis in field and laboratory conditions

Long

Millard

Smith³

1979

SUMMARYIn a laboratory trial chickens were given immunising doses of six species of Eimeria when they were 2 weeks of age and the effect of medication with monensin or arprinocid from 0-10 weeks was determined by challenge inoculation. Monensin in the food at 60-100 ppm resulted in depression of immunity but concentrations of 40-50 ppm only slightly affected immunity to challenge inoculation. Arprinocid at 50 ppm also greatly reduced the development of resistance to infection but 20 ppm did not.In a field experiment where chickens were exposed only to naturally occurring coccidial populations, the feeding of monensin (45 ppm) or dinitolmide (125 ppm) for 14 weeks did not affect the development of immunity to the indigenous coccidial populations. Monensin-treated birds appeared to be slightly better protected. Chickens treated with monensin reached their target body weight earlier and maintained it better than dinitolmidetreated chickens.

“…Many populations of chicken Eimeria species resistant to two or more anticoccidial drugs have been isolated from the field (see Warren et al, 1966;Hodgson et al, 1969;Williams, 1969;Millard, 1970;Ryley & Betts, 1973;Jeffers, 1974a,b;Chapman, 1980;Mathis & McDougald, 1982). There are several potential ways in which coccidial populations might have acquired such traits:…”

Section: Introductionmentioning

confidence: 99%

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

Williams¹

1998

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.