166 



THE TELOSPORASIDA AND THE COCCIDLA PROPER 



After coccidiostats had been mixed in 

 poultry feeds for a number of years, it 

 was inevitable that drug resistant strains 

 of coccidia would appear. The first report 

 of this was by Waletzky, Neal and Hable 

 (1954), who found a field strain of Eiiiieria 

 tenella resistant to sulfonamides. Cuckler 

 and Malanga (1955) reported on 40 field 

 strains of chicken coccidia which were re- 

 sistant to one coccidiostat or another, and 

 drug resistance is now a well-known com- 

 plicating factor in the use of these agents. 

 A race has developed between the coccidia 

 and the pharmaceutical houses, and some 

 day, horribile dictu, we may be reduced 

 to sanitation to control coccidia. 



Mixed Infections . All domestic ani- 

 mals have more than one species of coc- 

 cidia. Some are highly pathogenic, others 

 less so, and still others practically non- 

 pathogenic. Pure infections with a single 

 species are rare in nature, so the ob- 

 served effect is the resultant of the com- 

 bined actions of the particular mixture of 

 coccidia and other parasites present, to- 

 gether with the modifying effects of the 

 nutritional condition of the host and envi- 

 ronmental factors such as weather and 

 management practices. 



In the remainder of this chapter, each 

 species of coccidium in a particular host 

 animal will be taken up first, and then a 

 general discussion of coccidiosis in the 

 host will follow. 



Genus EIMEMA Schneider, 1875 



In this genus the oocyst contains 4 

 sporocysts, each of which contains 2 

 sporozoites. 



EIMERIA ALABAMENSIS 

 CHRISTENSEN, 1941 



Hosts : Ox. 



Location : Posterior half of ileum, 

 especially within a few feet forward from 

 the ileo-cecal valve. In heavy infections, 

 the cecum and upper colon may be in- 

 volved. 



Geographic Distribution : 

 America. 



North 



Prevalence : Davis, Boughton and 

 Bowman (1955) found this species in 93% 

 of 102 dairy calves in 6 herds in south- 

 eastern United States in a weekly fecal 

 survey; they found it in 24% of 135 animals 

 from which only a single fecal sample was 

 taken; it was present in all of 26 herds 

 from which at least 5 animals were ex- 

 amined. Hasche and Todd (1959) found it 

 in 42% of 355 cattle in Wisconsin. 



Morphology : The oocysts have been 

 described by Christensen (1941). They 

 measure 13 to 24 by 11 to 16 ji with a mean 

 of 18.9 by 13.4jLt. They are typically piri- 

 form but may also be subellipsoidal or sub- 

 cylindrical. The oocyst wall is thin, 

 delicate, homogeneous, transparent, color- 

 less to greyish-lavender to pale brownish 

 yellow, slightly thinner at the narrow end 

 but without a perceptible micropyle. Dur- 

 ing sporulation there is a parachute-shaped 

 cap at each end of the sporoblasts. Spor- 

 ulation takes 4 to 5 days. The sporocysts 

 are elongate and gently tapered. Neither 

 oocyst nor sporocyst residua are present. 

 A polar granule is presumably absent. 



Life Cycle : Davis, Bowman and 

 Boughton (1957) described the life cycle of 

 E. alabamensis . It is unusual in being an 

 intranuclear parasite, occurring within 

 the nuclei of the epithelial cells at the tips 

 of the villi. Excysted sporozoites were 

 seen in the cytoplasm of the intestinal 

 epithelial cells 2 days after infection. 

 They enter the nuclei and round up, form- 

 ing schizonts. These are present as early 

 as 2 days after infection and are uncommon 

 by the 8th day. They form 16 to 32 mero- 

 zoites, which are slender and spindle- 

 shaped while still within the parent schizont 

 but appear short, with bluntly rounded ends 

 in the intracellular spaces and crypts. 

 Davis, Bowman and Boughton (1957) thought 

 that there is probably more than one gen- 

 eration of schizonts. 



Macrogametes and microgametocytes 

 first appear 4 days after infection. Most 

 are found in the lower third of the small 

 intestine, but they may invade the cecum 



