566 



Protozoa of the Digestive and Urogenital Tracts 



Isospora hominis 



The life-cycle has not been traced completely although develop- 

 mental stages, possibly of /. hominis, were described by Virchow in 1860 

 and by Eimer in 1870. Oocysts also have been recovered from the small 

 intestine by aspiration through Miller-Abbott tubes (108). 



The oocyst (Fig. 11. 7, D-F) measures 25-33 x 12-16[j,. In freshly passed 

 stools, the zygote is usually undivided. A dividing zygote or two sporo- 

 blasts may be seen occasionally, and in cases of constipation, oocysts may 

 be passed with sporoblasts enclosed in spore membranes (108). The num- 

 ber of oocysts passed in the stools may increase and decrease in irregular 

 cycles of several days each (10), or the number may increase gradually 

 to a maximum and then decline steadily to zero (119). Development of 

 sporozoites, four in each of the two spores, has been observed in stools 

 kept at room temperature for 24-48 hours (120), although maturation 

 may require 60-72 hours at 70° F. (10). Passage of oocysts, which usually 

 begins as symptoms are abated, may continue for several weeks and 

 sometimes for two months or longer (108, 120). 



Effects on man 



Since intestinal Coccidia invade epithelial cells, tissue destruction 

 is inevitable. Although some cases are so mild that specific symptoms are 

 not evident (120), infection often leads to digestive disturbances with a 

 diarrhea persisting for several weeks. Symptoms in severe cases may in- 

 clude abdominal cramping, nausea, and lack of appetite (10). A typical 

 case, accidentally contracted in the laboratory, showed an incubation 

 period of six days, diarrhea for 22 days, and then normally formed stools 

 at the end of another week (35). A similar course has been described 

 for an experimentally induced infection (119). No relapses have been 

 reported. 



Chemotherapy 



No adequate treatment has been described. Recent data indicate 

 that standard courses of emetine, atebrin, quinine, carbarsone, tetra- 

 chlorethylene, chiniofon, and diodoquin have no significant effect on 

 duration of the infection (10, 108). However, the therapeutic and pro- 

 phylactic activity of sulfamerazine and sulfaguanidine in Eimeria tenella 

 infections of chickens (57) might suggest the possible value of such drugs 

 in human coccidiosis. 



