324 Sporozoa 



Subclass 1. Sarcoporidia 



The characteristic "cysts" of these organisms^ have been reported 

 mainly from striated muscles of reptiles, birds, and mammals, while forms 

 believed to be infective or developmental stages have been found in 

 the blood, in the intestinal epithelium and submucosa, and in the feces 

 of infected animals. Experimental infections have been produced by 

 feeding infected muscle tissue and also by the intra-muscular injection of 

 "spores." 



Much of the evidence indicates that infective stages are ingested by a 

 new host and that an intermediate host or mechanical vector is not neces- 

 sary. There are some reports that infection may occur in utero, but the 

 evidence is not entirely conclusive. The so-called "spores" of Sarcocystis 

 have been found in feces of infected sheep (121), and after experimental 

 feeding of laboratory animals, in the lumen of the intestine. In the intes- 

 tine of mice fed infected muscle, "spores" penetrate the mucosa and ap- 

 pear in the blood stream after 5-6 hours (3). Circulatory distribution of 

 the parasites is followed by invasion of muscle tissue and the eventual 

 development of sarcocysts (Fig. 6. 34, E-I). The time required for develop- 

 ment of typical sarcocysts has ranged from four to seven weeks after 

 feeding infective stages. 



Although this outline of the cycle seems to be based upon sound evi- 

 dence, the details of development are incompletely known. One important 

 gap is the scarcity of information concerning the "spores" after their 

 production in the sarcocyst. There is some evidence that sarcocysts occa- 

 sionally are ruptured and that the released parasites invade fresh tissue, 

 but the route followed in reaching a new host is yet to be determined. 

 The fact that "spores" have been recovered from the feces of various 

 hosts (121) might suggest that after rupture of a sarcocyst, some of the 

 parasites are transported through the circulatory system to the wall of 

 the intestine and from there migrate into the lumen. This would involve 

 retracing the route apparently followed in initial invasion. The obvious 

 difficulties in tracing such parasites through the tissues account for the 

 present lack of adequate information. 



The parasites may be found in the oesophagus, heart, diaphragm, 

 tongue muscles, and occasionally in other parts of the body. Invasion of 

 smooth muscle apparently is rare, if it occurs at all. The earliest stages 

 reported from muscles are single "sporoblasts" (Fig. 6. 34, E, F) and 

 groups of several such forms. Development of the mature cyst from these 

 stages has not been traced completely. The stage usually found in muscle 

 is the sarcocyst (Fig. 6. 34, I-K), the size and shape of which vary. The 

 larger sarcocysts are typically spindle-shaped in the diaphragm but are 



^Literature on the Sarcosporidia has been reviewed by Badudieri (4) and Scott (120, 

 12n. • 



