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==Clinical Signs==
==Clinical Signs==
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.
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'''.
==Epidemiology==
==Epidemiology==
The bacteria can survive in pond sediment and once a population of fish have recovered from an infection of ECS, they can become carriers. It can be found in the kidneys of fishes and is thought to be shed in the faeces of fish.
The bacteria can survive in pond sediment and once a population of fish have recovered from an infection of ECS, they can become '''carriers'''. It can be found in the kidneys of fishes and is 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 (Janda et al., 1991) and is not therefore zoonotic. Other environmental factors have been linked to outbreaks and include poor water quality, high stocking density and other stressors.
'''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 (Janda et al., 1991) 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'''.
==Distribution==
==Distribution==
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.
''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.
==Pathology==
==Pathology==
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. Skeletal muscle and areas of necrosis within internal organ tissue can be infiltrated with macrophages, that phagocytose the bacteria but do not destroy it (Miyazaki and Plumb, 1985; Klesius et al., 1991; Klesius, 1993;).
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. Skeletal muscle and areas of necrosis within internal organ tissue can be infiltrated with macrophages, that phagocytose the bacteria but do not destroy it (Miyazaki and Plumb, 1985; Klesius et al., 1991; Klesius, 1993;).