Eimeria infection of chicken embryos: the effect of known anticoccidial drugs against E. tenella and E. mivati.

The activity of nine anticoccidial drugs was investigated against Eimeria infections of chicken embryos. With Eimeria tenella, three parameters were used to assess the antiparasitic effects (a) mortality (b) focal lesions on the chorioallantoic membrane (CAM) and (c) oocyst production. Anticoccidial drugs against E. mivati were evaluated by estimating oocyst production only. Only three of the anticoccidials tested were found to have high activity when measured by all of the above criteria. All of the drugs tested reduced infections caused by E. tenella and E. mivati. With f. tenella, inhibition of CAM focal lesions and oocyst production proved to be more sensitive parameters than mortality of infected embryos. The number of sporozoites in the inoculating dose was important, particularly in the oocyst production studies because excessively large numbers of sporozoites did not result in high yields of oocysts. The application of chicken embryo infections with Eimeria for the study of anticoccidial drugs is discussed.