Abstract: A vaccine strain OU5758 is provided which includes an attenuated immunogenic plasmidless Salmonella enterica serovar-Typhimurium strain OU5046 harboring a recombinant plasmid pOU1500 for immunizing a chicken against leucocytozoonosis. The strain OU5046 is adapted to remain substantially avirulent, survive in vivo for at least a number of days, colonize within the chicken's liver, spleen, ovaries, or other internal organs, and express foreign antigens. The recombinant plasmid pOU1500 contains a gene encoding the circumsporozoite protein of the sporozoite of the chicken leucocytozoonosis parasite Leucocytozoon caulleryi. The vaccine strain OU5758 containing pOU1500 is capable of expressing circumsporozoite protein of L. caulleryi sporozoite, inducing anti-L. caulleryi immunity in chickens when ingested, reducing the frequency and severity of the disease's occurrence, and thereby enabling the chicken to maintain its normal egg production.