Elevated temperature exacerbates red sore disease caused by Vibrio vulnificus in American eels (Anguilla rostrata)

The marine pathogenic bacterium Vibrio vulnificus is linked to epizootics of a dermal ulcerative disease, causing high mortality in European and Japanese eels. American eels (Anguilla rostrata) experience a similar condition, commonly referred to as red sore disease (RSD). Field studies indicate that V. vulnificus infections highly correlate with RSD in American eels, but causation remains un-established. In this study, clinically healthy American eels were intraperitoneally injected with V. vulnificus and then held for 12 days at 18, 25, or 32°C. Presence of characteristic clinical signs, mortality, and consistent bacterial re-isolation fulfilled Koch's postulates for V. vulnificus as an etiological agent of RSD in American eels. Gross clinical signs included hyperemia, hemorrhage, epidermal erosion, and shallow to deep ulceration with sub-dermal tissue necrosis. Histopathology indicated widespread colonization by Gram negative bacteria; partial to complete loss of epidermis and dermis (including scales); as well as edema, hemorrhage, myonecrosis, and extensive leukocytic infiltration (inflammation) of affected tissues. Eels injected with V. vulnificus had 92 times higher odds of death than controls. Elevated temperature was an additional risk factor with the odds of V. vulnificus-injected eels dying being 13 times greater at 32°C compared to 18°C. This directly related to the increased growth of V. vulnificus at higher temperatures observed in vitro. These findings identify temperature as an important driver for RSD risk in wild American eel populations and a mitigation focus for eel aquaculture in the Chesapeake Bay region of the United States.