Pathogenesis of Erysipelothrix piscisicarius infection in tiger barbs (Puntigrus tetrazona)

Erysipelothrix piscisicarius is an emerging bacterial pathogen and the aetiologic agent of piscine erysipelosis, a recently recognized disease of ornamental fish. However, little is known regarding the dynamics of infection in fish. The purpose of this study was to gain a better understanding of the pathogenesis of piscine erysipelosis in the tiger barb (Puntigrus tetrazona) by investigating tissue tropisms and responses to bacterial dissemination following immersion challenge with a virulent strain recovered from diseased fish. The challenge resulted in 83% mortality by day 16. Erysipelothrix piscisicarius DNA was first detected in the skin using quantitative PCR, and bacteria were visualized in association with microscopic lesions on day 4. By day 8, E. piscisicarius DNA was further detected in intestines, hearts, spleens, gills and skin; parenchymal organs were largely spared. The data suggest a primary cutaneous portal of entry and tropism for collagenous tissues, particularly those within vascular walls. Initial spread occurs directly from the dermis into interstitial areas of skeletal muscle, then centrally to the peritoneum and coelomic cavity following collagenous tissue pathways. Although histopathology revealed widespread bacterial dissemination over time, the severity of skin and muscle lesions with high levels of bacterial DNA identifies these tissues as primary targets of infection.