Coccidiosis in turkeys is a disease of great economic importance to the poultry industry and ranks among the top 10 disease concerns for turkey veterinarians. Coccidiosis in turkeys is caused only by species of the genus Eimeria. The species of Eimeria causing turkey coccidiosis of economic importance to the industry are E. adenoeides, E. gallopavonis, E. meleagrimitis, and to a lesser extent E. meleagridis, E. dispersa, and E. innocua. Eimeria subrotunda is considered nonpathogenic. E. meleagridis is one species of turkey Eimeria where descriptions of endogenous development vary considerably among different researchers. E. meleagrimitis is a pathogenic species of turkey Eimeria causing catarrhal enteritis and mortality in severe cases. Eimeria species are known to exhibit a marked degree of host specificity; for example, species that infect the chicken are not infective to turkeys and vice versa. The infection resulted in an increase in subsets of T lymphocytes and alterations in cytokine profiles in the ceca of turkey poults.