Summary

# Editorial Summary Equine protozoal myeloencephalitis (EPM), caused primarily by *Sarcocystis neurona*, represents a significant neurological threat in the Americas, yet the epidemiology of *Sarcocystis* species exposure in South America remains poorly characterised. Borges-Silva and colleagues examined serological reactivity in 409 Brazilian horses using immunofluorescent antibody testing (IFAT) and Western blot analysis against both a local *S. falcatula*-like strain and the North American *S. neurona* strain, revealing that 10.5% of horses showed antibodies to *S. falcatula*-like, 17.1% to *S. neurona*, and 6.1% to both parasites. The poor agreement between the two IFAT results (κ = 0.364) and Western blot findings demonstrating cross-reactive epitopes (16–30 kDa protein range) suggest that Brazilian horses are exposed to multiple distinct *Sarcocystis* species generating different immune responses, rather than simple cross-reactivity from a single exposure. These findings carry important implications for equine practitioners in South America: seronegative results cannot exclude *Sarcocystis* exposure, seroprevalence estimates require species-specific antigen panels for accuracy, and the potential existence of geographically distinct strains may affect both EPM risk assessment and any future vaccine development programmes.

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Key Findings

• •10.5% of Brazilian horses (43/409) were seropositive to S. falcatula-like antigen
• •17.1% of horses (70/409) were seropositive to S. neurona antigen
• •6.1% of horses (25/409) tested positive to both parasites, indicating exposure to multiple Sarcocystis species
• •Proteins in the 16-30 kDa range are likely homologous between S. neurona and S. falcatula-like parasites

Conditions Studied

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