Multiscale oocyst wall mechanics govern coccidian resistance

Coccidian parasites spread through oocysts, environmental transmission stages that must survive harsh conditions yet rupture on cue inside the host to release infectious sporozoites. How the oocyst wall reconciles these opposing demands is unknown. Using single-oocyst microindentation, quantitative imaging and infection assays in Eimeria acervulina and Eimeria tenella, we show that the bilayered wall is functionally partitioned: the chemically fragile outer layer is mechanically dispensable, while the inner layer bears the mechanical load and remains impermeable to macromolecules and limiting osmotic exchange even after the outer layer is stripped. Oocysts behave as pressurised shells that fail preferentially at the anterior pole, a fixed mechanical weak point that channels sporocyst release regardless of where force is applied. Wall structure, autofluorescence, mechanics and infectivity prove dissociable: bleach removes the outer layer without weakening the wall or fully abolishing infectivity, whereas heat weakens the wall and abolishes infectivity while leaving the bilayered structure intact. These findings define a mechanical logic for coccidian oocyst resistance, disinfection and controlled excystation, and identify the inner wall as the critical target for inactivating environmentally transmitted parasites.