354 



BIOLOGY OF THE LABORATORY MOUSE 



COCCIDIA 



Eimeria falciformis (eimer). — Mice are commonly infected with E. 

 falciformis (Fig. 137). Although it has been listed as a coccidium 

 of the rat (22), several workers (43) have shown that it cannot be trans- 

 mitted to the rat nor can mice be infected with the rat coccidium, E. 

 miyairii. 



Development involves the schizogony and the sporogony cycles. Infec- 

 tion occurs by the ingestion of the mature oocysts, each of which gives rise 

 to eight sporozoites which enter the epithelial cells of the digestive tract and 

 there undergo schizogony. This occurs chiefly in the small intestine but 

 may also occur in the large intestine (43) or in the stomach (31). The 

 merozoites liberated from the schizonts may repeat the asexual cycle, or 



they may develop into microgametes and 

 macrogametes. Fertilization results in the 

 formation of a zygote which later develops 

 into the oocyst. These occur in the feces and 

 can readily serve for diagnosis. They are 

 subspherical and measure i6^ito2ijubyii 

 /i to 17 At. 



It is known that laboratory mice often 

 may carry a mild infection of E. falciformis. 

 Yet, Nieschulz and Bos (27) in studying the 

 course of infection found that mice free 

 themselves of an infection with E. falciformis within 26 days when prevented 

 from acquiring reinfection. They suggest that the chronic condition of 

 spontaneous infection is probably due to reinfection. 



E. falciformis is pathogenic, although in mild infections the hosts are 

 not injured very severely. Of 50 mice which Nieschulz and Bos experi- 

 mentally infected with the coccidium, 40 per cent died between the fourth 

 and eighth day after the infection. They reported that the death was due 

 chiefly to the breaking down of the intestinal epithelium by the schiozogony 

 forms. Wenyon (43) states that in acute infections the organisms may cause 

 acute enteritis. 



Cryptosporidium muris tyzzer, 1907; Cryptosporidium parvum tyzzer, 

 191 2. — Two other coccidia of the digestive tract of the house mouse are 

 Cryptosporidium muris Tyzzer (40) and a smaller species, C. parvum Tyzzer 

 (41). C. muris is found in the stomach while C. parvum lives in the small 

 intestine. They differ from Eimeria falciformis in that neither is intra- 



A. B. 



Fig. 137. — Stages in the 

 development of the oocyst of 

 Eimeria falciformis ( X 1 000) . 

 {From Wenyon.) 



