The development of resistance to glycarbylamide and 2-chloro-4-nitrobenzamide in Eimeria tenella in chicks

Abstract

A twofold increase in resistance to glycarbylamide was induced in a strain of Eimeria tenella in chicks. This strain remained susceptible to amprolium, nicarbazin, nitrofurazone, zoalene, 3,5-dinitrobenzamide, 2-chloro-4-nitrobenzamide (M & B 5921) and spiramycin.At least an eightfold resistance to 2-chloro-4-nitrobenzamide (M & B 5921) was developed in another strain of E. tenella. This strain was also resistant to nitrofurazone, zoalene and 3,5-dinitrobenzamide, but not to glycarbylamide, amprolium, nicarbazin and spiramycin.A single test showed no transfer of drug-resistance when the two resistant strains were given simultaneously to the same birds.When a small number of parasites of a glycarbylamide-resistant strain of E. tenella was introduced into a larger inoculum of the normal parent strain, the resistant individuals appeared to diminish in number during passages through untreated chicks.I wish to thank Mrs B. M. Mitchell, Miss C. A. Hitchcock and Miss J. Watkins for technical assistance at various stages of the work.