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Abstract
The bacterial genus Edwardsiella affects fish species worldwide and contains two of the most important pathogens in catfish aquaculture. With the recent reclassification of the genus into five separate species, clarification is needed on pathogenicity, host-microbe relationships, and effectivity of preventative tools. Vaccination of cultured catfish with an orally delivered Edwardsiella ictaluri live-attenuated vaccine is a promising disease prevention method. An added benefit is the E. ictaluri vaccine also offers some cross-protection against a second Edwardsiella species of importance, the newly identified Edwardsiella piscicida. Studies on host-pathogen interactions and immune responses to the vaccine, as well as natural Edwardsiella spp. infections in catfish, are in their infancy. Historical overlap between Edwardsiella tarda, Edwardsiella anguillarum, and E. piscicida has obscured accurate documentation of pathogenicity to different catfish varieties and associated disease processes, with E. anguillarum and E. tarda seemingly causing minimal disease in cultured catfish. Though less significant in catfish aquaculture, E. anguillarum, the most recently recognized Edwardsiella sp., is an emerging fish pathogen with an expanding host range, particularly in cultured tilapia. Information on E. anguillarum, most notably strategies for prevention and treatment, is limited due to previous mistaken identity and failure to recognize E. anguillarum as a discrete taxon separate from E. tarda. The overall objectives of the proposed research include: 1) characterizing intraspecific variability of E. anguillarum isolates in various fish species from different geographic locations, 2) comparing mortality and characterizing pathology associated with the recently reclassified Edwardsiella spp. (E. tarda, E. piscicida, E. anguillarum) in channel, blue, and hybrid catfish, and, lastly, comparing the susceptibility, immune responses, and pathologic changes between vaccinated and non-vaccinated, channel and hybrid catfish to experimental challenge with 3) E. ictaluri and 4) E. piscicida.