The partial protection against challenge with Eimeria tenella YFP (EiYFP) in chickens which were immunized with T. gondii. Leghorn chickens immunized s.c. with two doses of T gondii YFP (TgYFP) or wild type RH strain (5 × 106 for the initial immunization and 107 for the booster dose) or 160 μg recombinant YFP emulsified in Freund complete adjuvant (FCA). The immunized chickens were challenged with 103 transgenic E. tenella YFP 15 days after the booster immunization. A. Fluorescence images of transgenic E. tenella YFP oocysts. B. Fecal oocyst counts in chickens immunized with T. gondii YFP (TgYFP) or wild type T. gondii tachyzoites (Wild-Tg) or recombinant YFP emulsified in FCA (rYFP) or complete cytomix buffer (un-immunized control) and challenged with the transgenic E. tenella (EiYFP). C. Histopathology of the cecum from chickens described above in Figure B. C1 Shedding of mucosal cells (arrow); C2 Inflammatory cells infiltration of lamina propria (arrow).