A Novel Rhoptry Protein as Candidate Vaccine against Eimeria tenella Infection.

Xingju Song,Qun Liu,Xu Yang,Jing Liu,Taotao Zhang

doi:10.3390/vaccines8030452

Abstract

Eimeria tenella (E. tenella) is a highly pathogenic and prevalent species of Eimeria that infects chickens, and it causes a considerable disease burden worldwide. The secreted proteins and surface antigens of E. tenella at the sporozoite stage play an essential role in the host–parasite interaction, which involves attachment and invasion, and these interactions are considered vaccine candidates based on the strategy of cutting off the invasion pathway to interrupt infection. We selected two highly expressed surface antigens (SAGs; Et-SAG13 and Et-SAG) and two highly expressed secreted antigens (rhoptry kinases Eten5-A, Et-ROPK-Eten5-A and dense granule 12, Et-GRA12) at the sporozoite stage. Et-ROPK-Eten5-A and Et-GRA12 were two unexplored proteins. Et-ROPK-Eten5-A was an E. tenella-specific rhoptry (ROP) protein and distributed in the apical pole of sporozoites and merozoites. Et-GRA12 was scattered in granular form at the sporozoite stage. To evaluate the potential of rEt-ROPK-Eten5-A, rEt-GRA12, rEt-SAG13 and rEt-SAG proteins as a coccidiosis vaccine, the protective efficacy was examined based on survival rate, lesion score, body weight gain, relative body weight gain and oocyst output. The survival rate was significantly improved in rEt-ROPK-Eten5-A (100%) and rEt-GRA12 (100%) immune chickens compared to the challenged control group (40%). The average body weight gains of rEt-ROPK-Eten5-A, rEt-GRA12, rEt-SAG13 and rEt-SAG immunized chickens were significantly higher than those of unimmunized chickens. The mean lesion score and oocyst output of the rEt-ROPK-Eten5-A immunized chickens were significantly reduced compared to unimmunized challenged chickens. These results suggest that the rEt-ROPK-Eten5-A protein effectively triggered protection against E. tenella in chickens and provides a useful foundation for future work developing anticoccidial vaccines.

Highlights

Coccidiosis is caused by the genus Eimeria, and it is one of the most widespread and economically detrimental diseases affecting the global poultry industry [1,2]
The screening of surface antigens and secreted antigens that are highly expressed at the sporozoite stage is significant for the development of anticoccidial vaccines
Screening for surface antigens or secreted antigens that are highly expressed at the sporozoite stage is significant for the development of anticoccidial vaccines

Summary

Introduction

Coccidiosis is caused by the genus Eimeria, and it is one of the most widespread and economically detrimental diseases affecting the global poultry industry [1,2]. The annual loss due to coccidiosis exceeds $3 billion USD globally [3]. Eimeria tenella (E. tenella) is one of the most harmful species due to its wide prevalence and high pathogenicity [4]. Conventional control strategies primarily rely on anticoccidial drugs [3,6]. Alternative control strategies are urgently needed due to the rapid emergence of drug-resistant parasites, the high cost of new drug development and the increasing legislation restrictions on the use of anticoccidial drugs [7,8]. Live oocyst vaccines are used commercially in some regions, virulence variation

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