ABSTRACT

Background and Aim: Avian coccidiosis, caused by multiple Eimeria species, remains a major challenge to global poultry production due to its impact on animal health, productivity, and economic sustainability. Increasing genomic and molecular evidence highlights substantial genetic diversity within and between Eimeria species, which plays a critical role in shaping parasite virulence, host immune responses, vaccine efficacy, sensitivity to anticoccidial drugs, and diagnostic accuracy. This review synthesizes current knowledge on the mechanisms and consequences of genetic variation in chicken-infecting Eimeria species. Variations such as single-nucleotide polymorphisms, insertions/deletions, and copy number changes influence key functional proteins involved in host invasion and immune evasion. Antigenic diversity contributes to incomplete cross-protection and variability in vaccine performance, while mutations in drug-target genes are associated with the emergence of resistance to commonly used anticoccidials. Additionally, genetic heterogeneity complicates conventional and molecular diagnostic approaches, leading to potential misidentification and underestimation of infection prevalence. Advances in whole-genome sequencing and high-throughput diagnostic tools provide opportunities to better understand parasite diversity and improve disease control strategies. Overall, integrating genomic insights with vaccination, drug management, and diagnostic innovations is essential for developing sustainable and effective coccidiosis control programs in poultry systems. 

Keywords: anticoccidial resistance, chicken coccidiosis, diagnostic reliability, Eimeria diversity, genomic variation, immuno-genicity, vaccine efficacy, virulence.