A Search for Drug-Fast Strains of Eimeria tenella

Coccidiostatic drugs have come into widespread use because most epidemics of avian coccidiosis last for several weeks. Therefore, therapeutic treatments of a few days duration cannot prevent the major portion of the losses. But continuous medication with a coccidiostat suggests the possibility that these protozoa may become drug-fast. Furthermore, numerous complaints from poultrymen suggested to us that at least one drug might be less effective than formerly. Therefore, tests were designed to explore the possible existence of drug-fastness.