Chapter 4 



Protozoa parasitic in the digestive 

 tract (continued) 



Sporozoa 

 1. isospora honiinis (Rivolta 1878) 



THIS IS the sole coccidian parasite of man, and occurs 

 in the faeces in the oocyst stage. Judging from the 

 developmental cycle of other species parasitic in various 

 mammals, it is assumed that the organism undergoes 

 schizogony as well as sporogony in the epithelial cells of 

 the small intestine, thus destroying host's intestinal cells. 



Oocysts 



The oocyst (Fig. 12, 1-4) is fusiform in general outline, 

 but as a rule asymmetricallv drawn out at the two extremi- 

 ties. One end mav be bluntly pointed, while the other 

 often truncated. It is 20-33m long by 10-16m wide. The 

 wall is composed of two membranes and is remarkably re- 

 sistant to fixatives and stains, and therefore it can be far 

 more satisfactorily studied in fresh or unstained conditions 

 than in a stained smear. When freshly passed, the contents 

 either fill up the oocyst completely (Fig. 12, 1) or more 

 often appear as a spherical mass whose diameter coincides 

 with the inner width of the cyst wall (Fig. 12, 2). The 

 protoplasm is filled with refractile granules of various 

 dimensions, among which the nucleus mav appear as a 

 clear granule-free area. If a portion of the faeces contain- 



47 



