Eimeria necatrix: the development and characteristics of an egg-adapted (attenuated) line.

Sporozoites of Eimeria necatrix inoculated into the allantoic cavities of embryonating eggs completed their life-cycle in the chorio-allantoic membranes and produced fully viable oocysts. Subsequently, as a result of repeated passage in this host, an egg-adapted line was developed and was found to be markedly less pathogenic for chickens than the nonpassaged parent strain. Antigens capable of inducing protective immunity against challenge with low doses of the parent strain were retained, however, indicating a possible use for this egg-adapted (attenuated) line of E. necatrix in the immunization of commercially reared chickens.