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Also known as: Enteric Septicaemia of Catfish — Hole in the Head Disease — ESC.
Edwardsiella ictaluri belongs to the Enterobacteriaceae family and is a Gram negative, short, pleomorphic rod, measuring 0.75 × 1.5-2.5 µm, which is weakly motile at 25-30°C, but not at higher temperatures. It has peritrichous flagella and occasionally pili that can be seen with a scanning electron micrographs and can have between one to three plasmids depending on their molecular mass. It is generally considered an obligate pathogen, although it can survive in sterilised pond bottom mud for over 90 days but does not compete well with other microbes. The organism is lactose negative, catalase-positive, cytochrome oxidase-negative, glucose fermentative and reduces nitrate to nitrite.
E. ictaluri affects fish species only and causes enteric septicaemia of catfish (ESC) and various other species of fish. ESC is considered one of the most important infectious disease problems in the commercial catfish industry in the USA. Other species of Edwardsiella include E. tarda, which causes septicemia in fish and can affect other animals, whereas E. hoshinae infects birds and reptiles.
Within channel catfish species the bacteria cause two forms of ESC; an acute septicaemia and chronic encephalitis. In the latter form the infection spreads from the olfactory sacs, and migrates along the olfactory nerves to the brain, generating granulomatous inflammation. In the acute form of ESC, the disease is thought to develop from the intestinal mucosa causing a bacteremia.
Wild hosts include white, bullhead, blue, and wels catfish species and Japanese eel, Glass knifefishes, Tadpole Madtom, Rosy barb (minnow family), and species of carp called Devario devario .
Domestic hosts include white, walking, channel and sutchi catfish species and under experimental setting rainbow trout and chinook salmon.
With the chronic form of ESC clinical signs include, altered mentation, listlessness and chaotic swimming with ‘head-up, tail-down’ posture, circling and mortality. In later stages, the dorsum of the head swells and ulcerates revealing areas of the brain (hence the name ‘hole in the head disease’).
With acute forms of ESC you can see petechial haemorrhages around the buccal area, throat, abdomen and the fin base, that progress to depigmented ulcers. Fish generally suffer from moderate pale inflamed gills, exophthalmia, anaemia, haemorrhagic enteritis, systemic oedema, dropsy, ascites and splenomegaly. General behavioural changes include loss of balance, swimming near the surface, lethargy and cessation of feeding.
The bacteria can survive in pond sediment and once a population of fish have recovered from an infection of ECS, they can become carriers. They can be found in the kidneys of fishes and are thought to be shed in the faeces of fish.
Outbreaks are mainly seasonal and occur within a set temperature range of 18-28°C, primarily in spring and autumn. This temperature limitation precludes the bacterium from being a pathogen for humans or other warm-blooded animals  and is not therefore zoonotic. Other environmental factors have been linked to outbreaks and include poor water quality, high stocking density and other stressors.
E.ictaluri can invade the, gill mucosa, olfactory organ and nasal epithelium and nerve, brain meninges, skull and capillaries in the dermis of the skin.
E.ictaluri is mainly found in the USA, Asia and Thailand. The continual worldwide dissemination of channel catfish for aquaculture purposes may increase its future distribution.
Histological examination reveals a systemic infection of all organs and skeletal muscles, with the most severe changes being diffuse interstitial necrosis of the anterior and posterior kidney and systemic haemorrhages. Focal necrosis in the liver and spleen are also generally seen as pale grey/white lesions.
Clinical signs are quite pathognomonic for ESC but PCR is used to confirm the presence of E. ictaluri in blood and tissues but other methods have been used such as indirect FAT (detecting antibodies) and ELISA test.
The organism is slow growing and forms small, translucent, greenish colonies on Edwardsiella isolation media (EIM), while inhibiting Gram-positive and most Gram-negative contaminating organisms. E. ictaluri can be separated from E.tarda because it is indole-negative and does not produce H2S on triple sugar iron (TSI) agar.
Potentiated sulphonamide, sulfadimethoxine, methoprim or oxytetracycline have been used to treat ESC, but resistance has been recorded.
ESC may be controlled through reducing the amount of stress in fish stocks and cessation of feeding when outbreaks occur. A killed bacterin vaccine is available and administered in water by bath immersion.
Addition of the vaccine to feed may serve as a booster after vaccination as higher survival rates of fish given immersion plus oral applications than fish given double immersions.
Age-related factors and the induction of a cell mediated response are important in eliciting protection.
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- ↑ Shotts, E.B., Teska, J.D., (1989) Bacterial pathogens of aquatic vertebrates'. In: Austin B, Austin DA, eds. Methods for the Microbiological Examination of Fish and Shellfish. Chichester, UK: Ellis Horwood, 164-186.
- ↑ Janda, J., Abbott, S.L., Kroske-Bystrom, S., Cheung, W.K., Powers, C., Koka, R.P., Tamura, K., (1991) Pathogenic properties of Edwardsiella species. Journal of Clinical Microbiology, 29:1997-2001.
- ↑ Miyazaki, T., Plumb, J,A., (1985) Histopathology of Edwardsiella ictaluri in channel catfish, Ictalurus punctatus (Rafinesque). Journal of Fish Diseases, 8(4):389-392.(
- ↑ Klesius, P., Johnson, K., Durborow, R., Vinitnantharat, S., (1991) Development and evaluation of an enzyme-linked immunosorbent assay for catfish serum antibody to Edwardsiella ictaluri. Journal of Aquatic Animal Health, 3(2):94-99.
- ↑ Klesius, P.H., (1993) Rapid enzyme-linked immunosorbent tests for detecting antibodies to Edwardsiella ictaluri in channel catfish, Ictalurus punctatus, using exoantigen. Veterinary Immunology and Immunopathology, 36(4):359-368.
Evans, J., Klesius, P.H., Plumb, J.A. , Shoemaker, C.A. (2011). Edwardsiella Septicaemias. In: Fish Diseases and Disorders, Volume 3, 2nd edition (eds. P.T.K. Woo and D.W. Bruno), CABI, Wallingford, UK. pp. 512-569.
This article has been expert reviewed by Prof Patrick Woo MSc PhD
Date reviewed: 15 September 2011
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