160 



THE TELOSPORASIDA AND THE COCCIDIA PROPER 



MICROPYLE CAP 

 MICROPYLE 



SPORULATED 

 EIMERIA OOCYST 



POLAR GRANULE 

 STIEOA BODY 



SMALL REFRACTILE GLOBULE 

 IN SPOROZOITE 



LARGE REFRACTILE GLOBULE 

 IN SPOROZOITE 



SPOROCYST 



OOCYST RESIDUUM 

 SPOROCYST RESIDUUM 

 SPOROZOITE NUCLEUS 

 SPOROZOITE 



INNER LAYER OF OOCYST WALL 

 OUTER LAYER OF OOCYST WALL 



Fig. 23. Structures of sporulated Eiiiicria oocyst. 

 (Original) 



or more sporozoites. The microgametes 

 have 2 flagella. The genera are differen- 

 tiated by the number of sporocysts in their 

 oocysts and the number of sporozoites in 

 each oocyst. 



Morphology . The morphology of a 

 typical oocyst, that of Einieria, is shown 

 in Fig. 23. The oocyst wall is composed 

 of 1 or 2 layers and may be lined by a 

 membrane. It may have a micropyle, 

 which may be covered by a micropylar 

 cap. Within the oocyst in this genus are 

 4 sporocysts, each containing 2 sporozoites. 

 There may be a retractile polar granule in 

 the oocyst. There may be an oocyst resi- 

 duum or a sporocyst residuum in the oocyst 

 and sporocyst, respectively; these are com- 

 posed of material left over after the forma- 

 tion of the sporocysts and sporozoites. The 

 sporocyst may have a knob, the Stieda body, 

 at one end. The sporozoites are usually 

 sausage- or comma-shaped, and may con- 

 tain 1 or 2 clear globules. 



Location . Most coccidia are intra- 

 cellular parasites of the intestinal tract, 

 but a few occur in other organs such as the 

 liver and kidney. Each species is usually 

 found in a specific location within the in- 

 testinal tract; some are found in the cecum, 

 others in the duodenum, still others in the 

 ileum, etc. They may invade different 

 cells in these locations. Some species are 

 found in the mucosal cells at the tips of 



the villi, others in the crypts and still 

 others in the interior of the villi. Their 

 location within the host cell also varies. 

 Some species are found above the host 

 cell nucleus, while others are found be- 

 neath it and a few occur inside it. Some 

 species enlarge the host cell only slightly, 

 while others cause it to become enormous. 

 The host cell nucleus is also often greatly 

 enlarged even tho it may not be invaded. 



Life Cycle : The life cycles of the 

 Eimeriidae are similar, and can be illus- 

 trated by that of Ei»ieyia teiiella, which is 

 found in the ceca of the chicken (Fig. 24). 

 It was first worked out in a classic paper 

 by Tyzzer (1929). The oocysts are passed 

 in the feces; at this time they contain a 

 single cell, the sporont. They must have 

 oxygen in order to develop to the infective 

 stage, a process known as sporulation or 

 sporogony. The sporont, which is diploid, 

 undergoes reduction division and throws 

 off a retractile polar body. The haploid 

 number of chromosomes is 2 (Walton, 

 1959). The sporont divides to form 4 

 sporoblasts, each of which then develops 

 into a sporocyst. Two sporozoites develop 

 within each sporocyst. Sporulation takes 

 2 days at ordinary temperatures. The 

 oocysts are then infective and ready to 

 continue the life cycle. 



When eaten by a chicken, the oocyst 

 wall breaks, releasing the sporozoites. 

 The factors which cause excystation have 

 not been determined. Itagaki and Tsubo- 

 kura (1958) found that pancreatic juice did 

 not cause excystation of E. lenella, and 

 Landers (1960) was unable to induce ex- 

 cystation by treating the oocysts of E. 

 nieschulzi from the rat with pepsin, tryp- 

 sin, pancreatin, pancreatic lipase or bile. 

 Ikeda (1960), however, reported that pan- 

 creatic juice did cause excystation of E. 

 teiiella, and that trypsin was the respon- 

 sible enzyme. 



According to Challey and Burns (1959) 

 and Pattillo (1959), the sporozoites first 

 enter the cells of the surface epithelium. 

 Pattillo (1959) observed passageways, 

 which he called penetration tubes, in the 

 striated border and epithelium thru which 

 the sporozoites passed. They deploy along 



