From Abattoir to Analysis: Molecular and Epidemiological Characterization of Bovine Eosinophilic Myositis in Cattle Slaughtered in Portugal

Bovine eosinophilic myositis (BEM) is a myopathy detected during meat inspection, yet its epidemiology and relationship with Sarcocystis spp. remain poorly understood. This study provides the first epidemiological investigation of BEM and molecular characterization of Sarcocystis spp. in BEM-compatible lesions in Portugal. Between June and December 2024, BEM-compatible lesions were detected in 96 of 22,839 cattle. Most positive cases occurred in beef cattle (92/96; 95.8%), for which positivity was 0.57%, compared with 0.06% in dairy cattle. Beef cattle had nearly tenfold higher odds of presenting lesions compatible with BEM than dairy cattle (OR = 9.82; 95% CI: 3.71–36.81; BH-adjusted p < 0.001). Although sex, age, and native breeds were associated with lesions consistent with BEM in the univariable analysis, only female sex remained associated with positivity in the multivariable analysis. Histology identified sarcocysts in 41 of 81 samples; direct microscopy detected them in 34 of 66 samples. Among 123 isolated sarcocysts, 116 were identified as Sarcocystis cruzi from 32 cattle, 2 as Sarcocystis bovifelis, 4 as Sarcocystis heydorni, and 1 as Sarcocystis hominis, with the latter two being zoonotic species. Although the analysis of isolated sarcocysts does not allow estimation of species prevalence within lesions or establishment of a causal relationship with BEM, these findings provide the first epidemiological baseline for BEM in Portugal, expand current knowledge of the diversity of Sarcocystis species present in affected cattle, and offer valuable evidence to support risk-based meat inspection strategies and future multicenter One Health investigations into transmission dynamics and species-specific associations with BEM.