Eimeria brunetti: selection and characteristics of a precocious (and attenuated) line.

A line of Eimeria brunetti with an abbreviated life cycle (i.e. a 'precocious' line) was obtained by repeated selection for the first oocysts to be passed during an infection in chickens. The precocious line, when compared with the parent strain, was characterised by a significant attenuation of virulence, reduced output of oocysts and an endogenous development in which third-generation schizonts were almost completely eliminated. However, despite the loss of asexual stages, the immunogenicity of the precocious line was not different from that of its parent strain. A sub-line obtained from a single oocyst isolated after 27 generations of selection was further serially passaged using oocysts recovered during the peak of the patent period. The sub-line remained significantly attenuated after nine passages.