Transmission to eels, portals of entry, and putative reservoirs of Vibrio vulnificus serovar E (biotype 2)

Vibrio vulnificus serovar E (formerly biotype 2) is the etiologic agent tha t is responsible for the main infectious disease affecting farmed eels. Alt hough the pathogen can theoretically use water as a vehicle for disease tra nsmission, it has not been isolated from tank water during epizootics to da te. In this work, the mode of transmission of the disease to healthy eels, the portals of entry of the pathogen into fish, and their putative reservoi rs have been investigated by means of laboratory and field experiments. Res ults of the experiments of direct and indirect host-to-host transmission, p atch contact challenges, and oral-anal intubations suggest that water is th e prime vehicle for disease transmission and that gills are the main portal s of entry into the eel body. The pathogen mixed with food can also come in to the fish through the gastrointestinal tract and develop the disease. The se conclusions were supported by field data obtained during a natural outbr eak in which we were able to isolate this microorganism from tank water for the first time. The examination of some survivors from experimental infect ions by indirect immunofluorescence and scanning electron microscopy showed that V. vidnificus serovar E formed a biofilm-like structure on the eel sk in surface. In vitro assays demonstrated that the ability of the pathogen t o colonize both hydrophilic and hydrophobic surfaces was inhibited by gluco se. The capacity to form biofilms on eel surface could constitute a strateg y for surviving between epizootics or outbreaks, and coated survivors could act as reservoirs for the disease.