THE TELOSPORASTDA AND THE COCCIDIA PROPER 



169 



The micropyle is a lightened area at the 

 small end. The oocyst wall is smooth, 

 homogeneous, transparent, pale cloudy, 

 greenish brown to yellowish brown, and 

 slightly thinner toward the micropylar end. 

 The wall is not so delicate as that of E. 

 alaba))ieiisis. It is darker than that of E. 

 alabai)ieiisis and lighter than that of E. 

 aubnriiensis. Christensen (1941) illus- 

 trated the wall as composed of a heavy 

 inner layer and a very thin, transparent 

 outer layer, but he did not mention layers 

 in his description. An oocyst residuum 

 and polar granule are absent. A sporocyst 

 residuum is present. 



The sporulation time is 2 to 3 days. 



Life Cycle : Hammond et al. (1946) 

 described the endogenous stages of the 

 life cycle of E. bovis in detail. There is 

 a single asexual generation. The sporo- 

 zoites invade the endothelial cells of the 

 lacteals of the villi in the posterior half 

 of the small intestine. These cells be- 

 come detached from the lacteal lining and 

 lie free and greatly swollen in the lumens 

 of the lacteals. The schizonts are first 

 found 5 days after infection. They grow to 

 giant size, becoming mature 14 to 18 days 

 after infection. A few may still be found 

 as long as 30 days after inoculation, but 

 most of these are degenerate. The mature 

 schizonts measure 207 to 435 by 134 to 

 267 jLi with a mean of 281 by 303 ji and con- 

 tain 55,000 to 170,000 (mean, 120,000) 

 merozoites. They are easily visible to 

 the naked eye as whitish balls, and their 

 presence was first pointed out by Boughton 

 (1942) as a macroscopic lesion which could 

 be used in diagnosing coccidiosis. 



The merozoites are 9 to 15jj, (mean, 

 11.6jLi) long and about 2/i wide. They are 

 rounded at one end and taper abruptly to a 

 point at the other. The nucleus is near 

 the pointed end. 



The sexual stages usually occur only 

 in the cecum and colon, but in heavy in- 

 fections they may be found in the terminal 

 3 or 4 feet of the small intestine. They 

 occur in the epithelial cells of the intes- 

 tinal glands. The cells at the base of the 

 glands are invaded first, and later the 



rest of the gland becomes involved. The 

 first sexual stages appear 17 days after 

 inoculation. The macrogametes contain 

 plastic granules in their cytoplasm, there 

 being 1 layer of small granules near the 

 surface and a less distinct layer of larger 

 granules beneath it. Fertilization was not 

 seen, but 2 stages in the union of nuclei 

 were seen before formation of the oocyst 

 wall. 



According to Walton (1959), the hap- 

 loid number of chromosomes in E. bovis 

 is 2. 



Oocysts appear 16 to 21 days after 

 experimental infection. Large numbers 

 are discharged for 5 to 7 days, and 

 smaller numbers are present in the feces 

 for 2 to 3 weeks. In 28 calves studied by 

 Senger et al. (1959), oocysts were dis- 

 charged for 7 to 15 days with a mean of 

 11.5 days. 



Pathogenesis : E. bovis is one of the 

 2 most pathogenic of the bovine coccidia. 

 Hammond, Davis and Bowman (1944) 

 studied its effects in experimentally in- 

 fected calves. An infective dose of 

 125,000 oocysts or more was generally 

 needed to cause marked signs. These 

 appeared about 18 days after infection, 

 and consisted of diarrhea and/or bloody 

 diarrhea, tenesmus, and temperatures as 

 high as 106. 6° F. One of 4 calves given 

 125,000 oocysts become moribund due to 

 coccidiosis, while single calves given 

 250, 000 to 1, 000, 000 oocysts all died or 

 became moribund 24 to 27 days after in- 

 fection. 



The most severe pathologic changes 

 occur in the cecum, colon and terminal 

 foot of the ileum. They are due to the 

 sexual stages of the coccidia. At first 

 the mucosa is congested, edematous 

 and thickened, with petechiae or diffuse 

 hemorrhages. Its lumen may contain a 

 large amount of blood. Later, the mucosa 

 is destroyed and sloughed, and a patchy 

 or continuous membrane forms over its 

 surface. The sub mucosa may also be 

 destroyed. If the animal survives, 

 both mucosa and submucosa are later 

 replaced. 



