Ultrastructural changes in the oocyst wall during excystation of Cryptosporidium parvum (Apicomplexa; Eucoccidiorida)

Abstract

Cryptosporidium parvum oocysts were obtained from the feces of naturally infected calves and the oocyst wall was examined ultrastructurally. The oocyst wall averaged 49.7 nm thick and was composed of two layers. The outer layer was irregular in thickness, averaging 10 nm. A thin, electron-lucent space (2.5 nm) was interposed between the outer and inner layers. The inner layer had an outer (11.6 nm) and an inner (25.8 nm) zone. A suture that extended partway around the oocyst was observed within the inner layer of the oocyst wall. The suture underwent dissolution during excystation.