EtMIC2 overexpression attenuates pathogenicity while enhancing oocyst production and immunogenicity in Eimeria tenella.

Avian coccidiosis, caused by Eimeria parasites, is a devastating birds disease with global economic impacts. Despite its significance, the pathogenesis of E. tenella remains unclear due to genetic manipulation challenges. Previous studies have identified E. tenella microneme protein 2 (EtMIC2) as a critical factor for host cell invasion, but its precise role during developmental stages in vivo remains poorly characterized. To address this knowledge gap, we generated a genetically edited strain stably overexpressing EtMIC2 (EtMIC2-OE) and investigated the impact of EtMIC2 overexpression on E. tenella pathogenicity, oocyst production, and immunogenicity. Our findings demonstrate that EtMIC2 overexpression significantly impaired the parasite's invasion capacity and pathogenicity (P < 0.05). Intriguingly, during the sexual reproductive phase, EtMIC2-OE showed a substantial increase in oocyst output, probably mediated by the upregulation of sexual-stage-specific genes, such as EtGAM56. An immunization-challenge trial revealed that strain EtMIC2-OE showed markedly stronger immunogenicity than the parental strain, evident as an 80 % reduction in intestinal lesions (P < 0.001) and 99.5 % inhibition of oocyst shedding in the host (P < 0.001), and an improved anticoccidial index (195 vs parental strain's 160). Therefore, EtMIC2 not only plays a pivotal role in host cell invasion but may also be a key regulator of sexual reproduction. Furthermore, strain EtMIC2-OE shows strong potential utility as a live-attenuated vaccine candidate. This study provides novel insights into the mechanistic underpinnings of Eimeria biology and advances practical strategies for coccidiosis control.