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Överföringsmekanismer hos den fiskpatogena bakterien Flexibacter psychrophilus i vatten och fisk

Transmission mechanisms of the bacterium Flexibacter psychrophilus in rainbow trout

Flexibacter psychrophilus (syn.Flavobacterium psychrophilum, och Cytophaga psychrophila) är en fiskpatogen bakterie, som i ett flertal Europeiska länder inklusive Finland, angriper i huvudsak odlad regnbågslax.Bakterien kan förorsaka flera olika sjukdomstillstånd och hög dödlighet (upp till 80 - 90 %) hos yngel av regnbågslax.Sjukdomsutbrotten förekommer i huvudsak vid låga temperaturer.Bakterieangreppen behandlas främst med kemikaliebad eller antibiotikaterapi.Kommersiellt vaccin mot bakterien finns för tillfället inte tillgängligt.

Flexibacter psychrophilus (syn.Flavobacterium psychrophilum and Cytophaga psychrophila) was described for the first time in Finland in 1994, but the bacterium has most probably been present in Finland before the first description.F. psychrophilus has proven to cause mortality (up to 80 - 90 %) mainly in rainbow trout fry in Finland as well as in other countries.In fingerlings, grown up fish and brood fish (rainbow trout) lower but significant mortality rates have been recorded.Three different disease syndromes caused by F. psychrophilus have been described and outbreak of these diseases occur mainly when the temperature in the water is below ~15 C (often between 0 and 10 C).Since the diseases occur mainly in low temperatures antibiotic treatment is often difficult and generally not recommended due to the impact on the ecosystem and the possible spread of resisrance factors to human pathogens.So far there are no commercial vaccines available against F. psychrophilus.Thus the combat of the parhogen has to use other strategies, e.g. prevention of the spread of the pathogen and introduction of the pathogen into the fish.This can be achieved only if the epidemiology of the pathogen is well known.The aim of the present project plan is to 1) serologically, biochemically and molecularly characterize Finnish strains of F. psychrophilus, 2) improve rapid and reliable detection methods for F. psychrophilus, 3) determine the virulence capacity of surviving cells of F. psychrophilus in water and the shedding rate from infected fish, 4) identify mechanisms for the transmission of F. psychrophilus from fish to fish and from farm to farm, 5) identify mechanisms which causes the establishment of "carrier state" of F. psychrophilus in fish.The methods to be used for the detection and identification of the pathogen include serological, biochemical, immunofluorescence antibody technique, PCR technique, flow cytometric method, and plate count method.The infective capacity of cells in water in laboratory microcosms on host fish, the shedding rate into the water of cells from experimentally infected fish, the transmission of F. psychrophilus horizontally and vertically, and the establishment of carrier state in fish after exposure to the pathogen will be examined.The project plan will produce results that will improve rapid and exact diagnosis of flexibacteriosis in fish, give us epidemiological information necessary for efficient control of this disease, and give basic information necessary for the development of immunoprophylactic measures against this disease, i.e. especially vaccination.In the final end, the results produced will reduce the use of harmful chemicals (antibiotics, formalin, ..) in the fish farming industry tody and thus reduce the impact on the environment.

Publikation(er)

15.2.1996 / 5.5.1998