Micropyle and oocyst wall changes associated with chemically mediated in vitro excystation of Eimeria stieda1 and Eimeria tenella

Scanning and transmission EM techniques revealed wall structural features and changes associated with chemically mediated alteration of oocyst walls (phase 1) in the process of excysting in vitro the sporozoites of Eimeria stiedai and Eimeria tenella. SEM showed the excystation sequence to be (a) sinking of the micropyle, (b) wall rupture, mainly around the micropylar lid, but sometimes radiating down the outer wall from the micropyle and (c) infolding or inrolling of the lid. Freeze-fracture and thin section preparations showed crosssection and surface features of walls and intra-oocyst components. Oocysts were incubated in CO₂ and cysteine hydrochloride before microscopic examination.