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Natural and experimental infections with Flavobacterium psychrophilum in salmonid fish

Ekman, Elisabet (2003). Natural and experimental infections with Flavobacterium psychrophilum in salmonid fish. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae. Veterinaria, 1401-6257 ; 160
ISBN 91-576-6391-2
[Doctoral thesis]

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Flavobacterium psychrophilum, the aetiological agent of rainbow trout fry syndrome (RTFS) and bacterial cold-water disease (BCWD) causes problems in salmonid aquaculture worldwide. Fry are the most seriously affected with a septicaemic disease, often with high mortalities. Skin ulcers and fin lesions are common, especially in fish infected at later life-stages. To investigate if Swedish brood fish are infected with F. psychrophilum, Baltic salmon (Salmo salar) brood fish were sampled for bacteriological examination. Both male and female fish, without any clinical signs of disease, were found to be infected with F. psychrophilum at the time of spawning. The bacterium was isolated from internal organs and sexual products. This shows that the brood fish may serve as a reservoir for the bacterium and indicates vertical transmission as a route of infection. Intraperitoneal experimental infections were performed in three species of salmonids, i.e. rainbow trout, Atlantic salmon (Salmo salar), and sea trout (Salmo trutta) to evaluate any species-differences in susceptibility to the bacterium. Also, macro- and microscopical pathological changes, and the distribution of the bacterium, studied by immunohistochemistry, were evaluated. No species differences in mortality were recorded. Rainbow trout showed more pronounced changes in the spleen with haemorrhages, necrosis, and with numerous free bacteria present. A new experimental infection model, using nanoinjection of F. psychrophilum into newly fertilised rainbow trout eggs was performed to mimic vertical transmission of the bacterium. All infected groups showed higher mortalities compared with controls. Diseased fry showed clinical symptoms and morphological changes similar to RTFS. The nanoinjection method was also used to study the effects of exposure to polychlorinated biphenyls (PCB) on disease resistance to F. psychrophilum infection. Newly fertilised rainbow trout eggs were injected with a commercial blend of PCB (Clophen A50) and F. psychrophilum. The highest mortality was recorded in groups exposed to bacteria and the lowest dose of Clophen A50 whereas no effect on disease resistance was recorded in groups receiving the higher dose. The nanoinjection studies show that the method can be a useful tool to study vertically transmitted pathogens and that exposure to PCB might affect the disease resistance to vertically transmitted F. psychrophilum.

Authors/Creators:Ekman, Elisabet
Title:Natural and experimental infections with Flavobacterium psychrophilum in salmonid fish
Series Name/Journal:Acta Universitatis Agriculturae Sueciae. Veterinaria
Year of publishing :September 2003
Number of Pages:47
ALLI.Ekman, E., Börjeson, H. & Johansson, N. (1999) Flavobacterium psychrophilum in Baltic salmon Salmo salar brood fish and their offspring. Diseases of Aquatic Organisms 37, 159-163. II.Ekman, E. & Norrgren, L. (2003) Pathology and immunohistochemistry in experimental infection with Flavobacterium psychrophilum in three species of salmonids. Journal of Fish Diseases. In press III.Ekman, E., Åkerman, G., Balk, L. & Norrgren, L. (2003) Nanoinjection as a tool to mimic vertical transmission of Flavobacterium psychrophilum in rainbow trout Oncorhynchus mykiss. Diseases of Aquatic Organisms 55, 93-99. IV.Ekman, E., Åkerman, G., Balk, L. & Norrgren, L. Impact of PCBs on disease resistance in an experimental infection with Flavobacterium psychrophilum in rainbow trout Oncorhynchus mykiss eggs using nanoinjection technique. Manuscript submitted for publication.
Place of Publication:Uppsala
ISBN for printed version:91-576-6391-2
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:L Animal production > L73 Animal diseases
Subjects:Not in use, please see Agris categories
Agrovoc terms:fish diseases, histopathology, pathology, polychlorinated biphenyls, disease transmission, flavobacterium, fish culture
Keywords:bacterial cold-water disease, fish disease, histopathology, nanoinjection, rainbow trout fry syndrome, pathology, polychlorinated biphenyls, vertical transmission
Permanent URL:
ID Code:417
Department:(VH) > Institutionen för patologi
Deposited By: Elisabet Ekman
Deposited On:08 Dec 2003 00:00
Metadata Last Modified:02 Dec 2014 10:04

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