Insights into Genomic Sequence Diversity of the SAG Surface Antigen Superfamily in Geographically Diverse Eimeria Tenella Isolates

Eimeria tenella is among the protozoan parasites that cause the infectious disease coccidiosis in chickens, incurring huge economic losses to the global poultry industry. Surface antigens (EtSAGs) involved in host-parasite interaction are potential targets for control strategies. However, the occurrence of genetic diversity for EtSAGs in field populations is unknown, as is the risk of such diversity to the efficacy of EtSAG-based control approaches. Here, the extent of EtSAG genetic diversity and its implications on protein structure and function is assessed. Eighty-seven full-length EtSAG genomic sequences were identified from E. tenella genome assemblies of isolates sampled from continents including North America (United States), Europe (United Kingdom), Asia (Malaysia and Japan) and Africa (Nigeria). Limited diversity was observed in the EtSAG sequences. However, distinctive patterns of polymorphism were identified between EtSAG subfamilies, suggesting functional differences among these antigen families. Polymorphisms were sparsely distributed across isolates, with a small number of variants exclusive to specific geographical regions. These findings enhance our understanding of EtSAGs, particularly in elucidating functional differences among the antigens that could inform the development of more effective and long-lasting anticoccidial control strategies.