THE TELOSPORASIDA AND THE COCCIDIA PROPER 



213 



Fig. 29. Location of chicken coccidia in regions of the intestinal tract. A. Eiiiivrui 

 tenella. B. E. mitis. C. E. acervuliiia. D. E. niaxiiiia. E. E. i/ccalrix. 

 F. E. brnnetti. (A-D after Tyzzer, 1929; E after Tyzzer, Theiler and Jones, 

 1932; F after Boles and Becker, 1954) 



between species by cross-immunity stud- 

 ies, and indeed it was by means of such 

 studies that Levine (1938), for instance, 

 was able to show that E. hagani was a 

 valid species. 



Immunity against coccidia is seldom 

 solid. Birds which have recovered may 

 be reinfected, but such infections are 

 light and do not cause disease. Carriers 

 are extremely common and are a source 

 of infection for other birds. Thus, Levine 

 (1940) found E. mitis, E. acervnlina or 

 both in 53%, E. praecox in 33%, E. max- 

 ima in 28%, E. necatrix in 38% and£. 

 tenella in 23% of 39 pullets 8 months or 

 more old, but only 8% of them had gross 

 lesions. 



Heredity is a factor in resistance to 

 coccidiosis. Herrick (1934) found that 

 chicks from resistant parents were about 

 100% more resistant to E. tenella than 



unselected chicks. Champion (1954) and 

 Rosenberg, Alicata and Palafox (1954) 

 established E. teiiella-res\sia.nt and sus- 

 ceptible lines of chickens by selective 

 breeding. They found that sex linkage, 

 passive transfer of immunity thru the egg 

 and cytoplasmic inheritance did not play a 

 significant part in resistance and suscep- 

 tibility. Champion considered that they 

 were controlled in large part by non-dom- 

 inant, multiple genetic factors which pre- 

 sumably act additively. Rosenberg et al. 

 also thought that the factor or factors for 

 resistance or susceptibility did not show 

 marked dominance. 



Immunity in older birds is due mostly 

 to previous infection. The birds are ex- 

 posed repeatedly and almost continuously, 

 and their immunity is continually being 

 reinforced. Coccidiasis is thus extremely 

 common- -and indeed normal under natural 

 conditions- -while coccidiosis is the result 



