The Disease
Introduction
Enteric septicemia of catfish (ESC) is considered, both biologically and economically, as the most important disease of farm-raised channel catfish, particularly in the USA. ESC causes millions of dollars in losses annually to the USA catfish farming industry due to morbidity, mortality and lost production potential. The acute disease is now commonly known as ESC but chronic infections are also known as “hole-in-the-head” disease.
ESC disease may have been present since 1969 but was first recognised and differentiated from a closely related but distinctly different disease of catfish caused by Edwardsiella tarda in 1976 and not actually described in the literature in 1979. However, the causative agent of ESC disease, Edwardsiella ictaluri, was not actually described as a new species until 1981.
Etiology
ESC is caused by the Gram negative enteric bacteria Edwardsiella ictaluri. It is closely related to E. tarda, another pathogen of warmwater fish, but the two organisms cause distinctly different clinical diseases and are easily differentiated in the laboratory on the basis of biochemical and serological tests.
Classification of the Causative Agent
Eubacteria, family Enterobacteriaceae, genus Edwardsiella, species E. ictaluri. It is a Gram-negative, motile, facultatively aerobic, nonsporulating bacterium that is serotypically homogeneous.
Survives 3-4 months in pond water, mud, and vegetation.
Faecal-oral, cannibalism and direct contact
Indirect transmission by water, and contaminated materials used in handling.
Sources of the Agent
Faeces are the main source of shedding and dissemination, although dead fish and inanimate vectors (fishing nets, sorting devices) may be involved in contamination.
Carriers: in addition to catfish recovered from the disease, the bacterium seems to be able to survive in the intestinal tract of different fish species.
