Transitions in morphological forms and rapid development of the asexual schizonts of Eimeria tenella through serial passaging in chicks

Attenuated strains of avian Eimeria parasites, generated by the selection of precocious lines through serial passaging in chicks, have been used widely as live vaccines. Detailed morphological transitions including their life cycle depending on the passages remain poorly understood. Here, we showed early development and acceleration of transitions in morphological forms of the asexual schizonts of E. tenella that had been attenuated for virulence by serial passaging. Our results may be helpful in understanding parasitism, facilitating further molecular analyses such as comparative genomic or transcriptomic tests. [Display omitted] •E. tenella was attenuated by selection of precocious lines through passaging in chicks.•Precocity in 10-times-passaged strains may reflect accelerated development of the asexual schizonts.•Size reduction of the 2nd schizonts (the most pathogenic stage) after an additional 10 rounds of passaging may reflect attenuation.•Our results may be helpful for understanding parasite biology in the context of further molecular studies.