Ultrastructure of Cryptosporidium parvum oocysts and excysting sporozoites as revealed by high resolution scanning electron microscopy.

Cryptosporidium parvum oocysts isolated from calf feces were examined by scanning electron microscopy during excystation. Intact C. parvum oocysts were spheroid to ellipsoid, approximately equal to 3.5 X 4.0 micron, with length : width ratio = 1.17. The oocyst wall had a single suture at one pole, which spanned 1/3 to 1/2 the circumference of the oocyst. During excystation the suture dissolved, resulting in a slit-like opening, which the sporozoites used to exit the oocyst. Sporozoites were 3.8 X 0.6 micron and had a rough outer surface.