Development and Evaluation of a Recombinant Attenuated Salmonella Enteritidis Vaccine Expressing the EnGAM59 Gametocyte Antigen of Eimeria necatrix for Coccidiosis Control.

Gametocyte proteins are precursors of the oocyst wall proteins in Eimeria and play a crucial role in the development of immune-blocking vaccines and in reducing oocyst output. In this study, the gametocyte antigen gene Engam59 from E. necatrix was selected to construct eukaryotic expression plasmid pVAX1-Engam59. This plasmid was then transferred into the attenuated Salmonella Enteritidis strain Z11ΔrfbG to construct the live vector vaccine Z11ΔrfbG(pVAX1-Engam59). The immune protective efficacy of the Z11ΔrfbG(pVAX1-Engam59) was subsequently evaluated through chicken immune protection trials. The results showed that pVAX1-Engam59 was successfully expressed in Hek293t cells and was successfully transferred into Z11ΔrfbG. In vivo organs colonization tests showed that Z11ΔrfbG(pVAX1-Engam59) was more easily cleared by the host compared to Z11 wild-type strain. By day 14 post-infection, no bacteria were detected in the spleen or liver, and only a low amount of bacteria were found in the intestine. Chicken immune protection trials further revealed that immunization with Z11ΔrfbG(pVAX1-Engam59) stimulated lymphocyte proliferation and increased the levels of both anti-coccidial and anti-Salmonella antibodies in chickens. The anti-coccidial index (ACI) for chickens orally and intramuscularly administered Z11ΔrfbG(pVAX1-Engam59) was 157.7 and 157.9, respectively, indicating a moderate level of protection against coccidiosis. This study provides the foundation for the development of new live vector vaccines against coccidiosis.