Erysipelothrix rhusiopathiae, a re-emerging pathogen: a case report in laying hens from a cage-free farm

Erysipelas, caused by Erysipelothrix rhusiopathiae, has re-emerged as a significant threat in cage-free poultry systems. In May 2025, we investigated a sudden increase in mortality on a commercial layer farm in Chile. Eleven hens were necropsied, revealing systemic lesions consistent with septicemia. Erysipelothrix rhusiopathiae was isolated from multiple organs and confirmed through biochemical testing, histopathology, and PCR, identifying serotype 1b. Antimicrobial susceptibility testing showed marked sensitivity to β-lactams and resistance to fluoroquinolones, macrolides and tetracyclines. The outbreak was successfully controlled with amoxicillin therapy. This case highlights the increased risk of infectious diseases associated with cage-free production and underscores the need for continued diagnostic surveillance and antimicrobial resistance monitoring.