212 



THE TELOSPORASIDA AND THE COCCIDL\ PROPER 



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Fig. 28. Location of avian coccidia in intestinal epithelium of chicken. 1. Cryplo- 



sporidium tyzzeri. 2. Eimeria aceri'idina. 3. Eiineria iiiilis. 4. Eimeria 

 maxima. 5. Eimeria tenella. (From Tyzzer, 1929 in the American Journal 

 of Hygiene, published by the Johns Hopkins Press) 



The disease picture depends upon the 

 number of oocysts of each species which 

 the birds ingest. If they get only a few, 

 there are no signs, and repeated infec- 

 tions produce immunity without disease. 

 If they get more, the disease may be mild 

 and the birds will become immune. Only 

 if they get a large number of oocysts do 

 severe disease and death result. 



Crowding and lack of sanitation greatly 

 increase the disease hazard. As the 

 oocysts accumulate, the birds receive 

 heavier and heavier exposures, and the 

 disease becomes increasingly severe in 

 each successive batch of birds placed in 

 contaminated surroundings. 



Immunity: Coccidiosis is a self- 

 limiting disease, and birds which have re- 

 covered become immune. The speed with 

 which immunity develops depends upon the 

 species of Euneria and on the intensity and 

 frequency of infection. Immunity develops 

 rapidly following infections with E. »iax- 

 ima, E. praecox and probably E. hagani, 

 somewhat more slowly following infections 

 ■with E. tenella and E. briiiietli, and is de- 

 layed following infections with E. mills, 

 E. acervulina and£. necatrix. 



Immunity is species-specific. Chick- 

 ens which have become immune to one 

 species are susceptible to all the others. 

 This fact makes it possible to differentiate 



