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

A line of Eimeria necatrix with an abbreviated life cycle (i.e. a "precocious" line) was derived from the Houghton laboratory strain by repeated passage of the oocysts which were the first to be recovered from infections in chickens. The precocious line had a reproductive potential much lower than that of its parent strain and it was significantly less pathogenic. Its immunogenicity was, however, substantially retained. Selection for precocious development was accompanied by changes in the endogenous development of the parasite with an attendant reduction in its prepatent time.