Conserved proteins of Eimeria and their applications to develop universal subunit vaccine against chicken coccidiosis

Chicken coccidiosis caused by the Eimeria parasites, including E. acervuline, E. brunetti, E. maxima, E. mitis, E. necatrix, E. praecox and E. tenella, is one of the most economically important chicken diseases. The main measure to control chicken coccidiosis is chemoprophylaxis. However, the concerns of public about the over chemical residues in products and the strict legislation to limit the applications of drugs and the residues in products push chicken farmers to turn to the vaccination strategy to control coccidiosis. While the antigen diversity of Eimeria significantly decreased the traditional live vaccines. The cryptic strains of Eimeria, which have recently appeared and spread widely, can evade all commercial coccidiosis vaccines, thus becoming an emerging threat to global poultry production. For this reason, the development of universal subunit vaccines using the conserved proteins of Eimeria, effective against all species including the cryptic strains infecting chickens, is crucial for the sustainable development of global poultry industry. In this article, we reviewed the research progresses on the conserved proteins of Eimeria, including stage conserved proteins, species conserved proteins and both stage and species conserved proteins, with their possible applications in the development of universal subunit vaccines. Meanwhile, the cytokines and polymer-based nanomaterials used as adjuvants to enhance the protections of subunit vaccines were also summarized.