Characterization of Host Immune Responses to Eimeria adenoeides Infection in Turkey Poults

Coccidiosis is a common enteric disease of turkeys that is caused by protozoan parasites belonging to the genus Eimeria. There are about seven species of Eimeria that affect turkeys and of these E. adenoeides is the most pathogenic and commonly recognized. Infection with Eimeria is known to induce a long lasting protective immunity in chickens, but nothing is known regarding the acquisition of immunity to Eimeria in turkeys. The experiments reported here were aimed at investigating the biological and cellular immune response to E. adenoeides in turkey poults under different conditions of exposure. In experiment 1 (Chapter II), 20 day old poults were infected with 12.5 × 103 oocysts and shown to develop immunity when challenged with a high dose of oocysts at 34 days of age, as judged by weight gain and oocyst production. Changes in peripheral blood leukocytes following the primary exposure were investigated, and an increase in the number of total lymphocytes, monocytes, and subsets of lymphocytes (CD4+ and CD8+) was shown in infected poults compared to uninfected controls. In experiment 2 (Chapter III), local immune activities occurring in the ceca in response to infection were investigated. An increase in leukocyte infiltration, percent area occupied by CD4+ and CD8+ lymphocytes, and relative expression of cytokines (CXCLi2, IL1β, IFNγ, IL10, and IL13) was observed in the ceca following infection. In experiment 3 (Chapter IV), we attempted to model the field situation by investigating the acquisition of immunity under conditions poults could encounter following placement upon built-up litter. Results indicated that they had acquired partial protection judged by weight gain and mortality by day 12 and 18 following challenge. The leukocyte infiltration score, percent area occupied by CD4+ and CD8+ lymphocytes, and expression of the cytokines (CXCLi2, IL1β, IFNγ, IL2, IL10, IL12b, IL13, and IL18) in the ceca significantly increased following infection. The changes in the ceca of E. adenoeides infected poults, in terms of infiltration of leukocytes, the area occupied by various subsets of lymphocytes, and the relative expression of chemokines and cytokines characterize the development of innate and adaptive immune activities