Kurzbeschreibung
(Englisch)
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Fish provides more than 2.6 billion people with at least 20 percent of their average per capita animal protein intake. Aquaculture accounted for 43 percent of the 106 million tonnes of food fish in 2004 and its part continues to increase faster than any other animal food-producing sectors.
Worldwide, the sector has grown at an average rate of 8.8% per year since 1970. However, infectious fish diseases threat the development of this industry and pathogen control has now become a major concern (FAO, SOFIA, 2006 report).
Members of two genera in the family Flavobacteriaceae (or flavobacteria) (Jooste PJ & Hugo CJ.,1999), the freshwater Flavobacterium species and the marine Tenacibaculum species, are recognized as major problems for the aquaculture industry in Europe and worldwide (Nematollahi A. et al., 2003; Avendaño-Herrera R et al., 2006).
Three members of the genus Flavobacterium are recognized fish pathogens. Among them, Flavobacterium psychrophilum (Fp) is one of the most prevalent and troublesome infectious agents in salmonid farming worldwide that profoundly impacts the European salmon and rainbow trout production. Fp is the agent of cold water disease (CWD) and rainbow trout fry syndrome (RTFS).
These conditions occur most frequently at water temperatures between 3°C and 15°C and they can result in considerable economic losses due to high mortality in fry and juvenile fish, product quality problems (from skin ulcerations to vertebral deformation), increased susceptibility to other pathogens, elevated labor costs, and the need for chemotherapeutics (Nematollahi A. et al., 2003 & Holt RA et al., 1993). Salmonids showing signs of CWD are frequently treated with oral antibiotics, but resistance is increasingly common (e.g., to trimethoprim–sulfadiazine, oxolinic acid, gentamicin, neomycin, polymyxin B and tetracycline). Fry are especially affected with mortalities
up to 50-60%. Recent spreading of this bacterium in new geographical areas is especially striking.
Tenacibaculum maritimum (Tm) is causing a disease mostly characterized by skin and muscle ulcers that is responsible for low but constant mortality in many cultured marine fish worldwide (Avendaño-Herrera R et al., 2006). Many European salt-water fish farms suffer Tm infections because of its wide host range that includes many valuable species such as sole, turbot, sea bass, sea bream, meagre, sea trout and salmon.
The ultimate tool for controlling infections is to obtain efficient vaccines, but no commercial vaccines against Fp and Tm are available so far (Håstein T et al., 2005). In order to cope with the diseases, farmers rely on the recurrent use of antibiotics that is incompatible with the development of a sustainable aquaculture. Therefore, disease prevention is likely the most cost-effective control option. Most fish disease management strategies attempt to minimize the risk factors associated with horizontal transmission of the pathogens. Moreover, in the case of Fp there is strong evidence that vertical transmission also occurs, as the bacterium has been frequently found associated to eggs
(on the surface or, more speculatively inside) and in the ovarian fluid of infected broodstock that may be a major source of Fp transmission within fish farms (Madsen L et al., 2005).
However, accurate diagnosis of the causative agents is difficult and time-consuming and new fast diagnostic tools are urgently needed. They are critical for a fast identification of the pathogen responsible for the outbreaks, for epidemiological investigations (e.g., exploration of the pathogen propagation by global trade of fish and fish eggs, persistence in the environment, etc.) and for quantifying the level of infection in broodstocks (Madetoja J & Wiklund T., 2002).
The diversity and population structure of these pathogens are still poorly understood and the genomic data available are still sparse. A complete genome sequence and a preliminary multi-locus sequence typing (MLST) study have been published only for Fp (Duchaud E. et al., 2007 & Nicolas P. et al., 2008). This lack of knowledge hampers the development of diagnostic tools and effective vaccines. It also precludes the implementation of efficient control strategies based on the reduction of the transmission rates.
The advent of whole-genome sequencing of bacteria and advances in bioinformatics have revolutionized the study of bacterial pathogenesis, enabling the targeting of new diagnostic tools and possible vaccine candidates starting from genomic information. Nowadays, high throuput sequencing enables identification of the genetic differences across several genomes from the same species. The unexpected degree of intra-species diversity implies that a single genome sequence is not entirely representative and does not offer a complete picture of the genetic makeup of a species.
The practical consequence is that, in many cases, a universal vaccine is possible only by including a combination of antigens and this combination must take into account the pathogen population structure.
For this reason, eight of the main actors in this field in Europe have decided to combine their expertise and efforts to generate new scientific knowledge on Fp and Tm in order to develop rational diagnostic tools and efficient vaccines.
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Publikationen / Ergebnisse
(Englisch)
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Publications, posters and presentations
Streppavara, N.; Wahli, T.; Segner, H.; Polli, B.; Petrini O. (2012) Fluorescent in situ hybridization: a new tool for the direct identification and detection of Flavobacterium psychrophilum. PLoS One 7: e49280.
Strepparava, N.; Nicolas, P.; Wahli, T.; Segner, H.; Petrini, O. (2013) Molecular epidemiology of Flavobacterium psychrophilum from Swiss fish farms. Diseases of Aquatic Organisms 105: 203 - 210.
Strepparava, N.; Wahli, T.; Segner, H.; Petrini, O. (2014) Detection and quantification of Flavobacterium psychophilum in water and fish tissue samples by quantitative real time PCR. BMC Microbiology 14: 105.
Strepparava, N.; Segner, H.; Petrini, O.; Wahli, T. (2012) MALDI-TOF MS for the identification and characterization of Flavobacterium isolates from water and environment. Flavobacterium 2012: The 3rd international Conference on Members of the Genus Flavobacterium. Turku, Finnland. 5 – 7 June 2012
Wahli, T.; Hirschi, R.; Strepparava, N. (2014) Vergleich verschiedener Nachweismethoden für Flavobacterium psychrophilum. XV. Gemeinschaftstagung der Deutschen, Österreichischen und Schweizer Sektionen der EAFP, 8 - 10 Oktober 2014, Starnberg.
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