Molecular and histopathological evaluation of intestinal mucosal damage associated with coccidiosis in naturally infected lambs.

Coccidiosis, caused by Eimeria species, is a major cause of economic loss in sheep farming, leading to diarrhea, growth retardation, and mortality in young animals. This study aimed to characterize the intestinal pathology of naturally acquired coccidiosis in lambs and to evaluate the molecular response of the intestinal mucosa through the expression of five target genes. Lambs were classified into Control, Mild, Moderate, and Severe groups (n = 6/group) based on histopathological scoring of seven parameters: villus morphology, epithelial integrity, parasitic burden, epithelial hyperplasia, crypt alterations, inflammatory infiltration, and hyperemia/hemorrhage. Relative mRNA expression of FABP2, TFF3, ALPI, CLDN3, and ACTG2 was quantified by RT-qPCR and analyzed using the 2⁻ΔΔCt method. All histopathological parameters increased significantly with disease severity, with the main divergence occurring between Control/Mild and Moderate/Severe groups. FABP2 showed a linear, severity-dependent increase across all severity stages, whereas TFF3 and CLDN3 were significantly elevated only in Moderate and Severe groups. ALPI displayed a biphasic pattern, increasing in Mild and Moderate groups but returning to near-baseline levels in the Severe group, suggesting exhaustion of compensatory capacity. ACTG2 expression remained stable across all groups, indicating that tissue damage was confined to the mucosal and submucosal layers. These findings demonstrate that coccidiosis induces a threshold-dependent, multi-layered molecular response in the ovine intestine and suggest that a combined biomarker panel may improve the assessment of disease severity beyond conventional histopathology.