Recovery and viability of Edwardsiella ictaluri from great blue herons Ardea herodias fed E-ictaluri-infected channel catfish Ictalurus punctatus fingerlings

Feeding activities of great blue herons Ardea herodias in catfish ponds dur ing outbreaks of enteric septicemia of catfish have been implicated as a me chanism for the transmission of the disease from infected to uninfected pon ds. Although Edwardsiella ictaluri, the causative agent, has been identifie d in gastrointestinal tracts of great blue herons, the role of these birds as a vector of E. ictaluri is not well documented. The potential of these b irds to contaminate catfish ponds with E. ictaluri was investigated by feed ing captive herons over a 4-d period with catfish fingerlings injected intr aperitoneally with live E. ictaluri. Daily fecal samples, throat and rectal swabs, and feather samples were collected, cultured and examined for E. ic taluri using both a selective media and a monoclonal indirect fluorescent a ntibody test specific for E. ictaluri. Gastrointestinal tracts sampled at t he conclusion of the feeding trial were similarly examined. While E, ictalu ri was detected using the indirect Fluorescent antibody test, no viable E. ictaluri was cultured from either feces, gastrointestinal tracts or feather s. Growth of E. ictaluri was not observed at 40 C, the rectal temperature o bserved in captive great blue herons. Prior incubation at 40 C suppressed t he growth of E. ictaluri at 24 C, an optimal temperature for growth of this bacterium. These results indicate that great blue herons appear to play li ttle or no role in the transmission of E. ictaluri among catfish ponds.