Anticoccidial activity of an azauracil derivative

Abstract

A substituted azauracil derivative has been shown to have marked anticoccidial activity. Chickens given large challenge doses ofEimeria tenellawere protected from mortality by a dietary level of 0·25 ppm drug, while oocyst output was controlled by 10 ppm. Under conditions of continuous medication using 15 ppm of the azauracil derivative the development ofE. tenellawas arrested at the multinucleate first generation schizont stage; in the majority of parasites merozoite differentiation was inhibited. Experiments using restricted medication indicated that, withE. tenellain the chick, the drug was coccidiocidal rather than coccidiostatic, and that treatment for as little as one day could control the infection. Medication started during the second asexual cycle again resulted in inhibition at the multinucleate schizont stage just before merozoite differentiation. Mortality in birds inoculated withE. brunettiwas controlled by 1 ppm azauracil in the diet and oocyst output by 2.5 ppm; unlike the situation withE. tenella, the drug had no influence on the first two asexual cycles of reproduction. There was some inhibition of the third schizogony cycle, but the main effect of the drug in the case ofE. brunettiwas found to be against sexual reproduction. Effects similar to those notedin vivowere seen withE. tenellaandE. brunettigrowing in tissue culture. Occasional schizonts ofE. tenellaunder the influence of drug were able to produce a peripheral array of merozoites surrounding a multinucleate residual mass. In contrast to the situationin vivo, with drawal of drug from tissue cultures infected withE. tenellaallowed the further development of some inhibited parasites.E. necatrixresponded to the azauracil derivative in a manner similar toE. tenella.