The influence of infective dose, nutrient availability and coinfection on virulence of Flavobacterium columnare : implications of intensive aquaculture on opportunistic infections
Ecological factors are known to affect disease dynamics and even lead to disease
emergence. Especially in opportunistic, environmentally transmitted pathogens,
the environment may significantly contribute to pathogen virulence. Intensive
farming, including aquaculture, has been suggested to create conditions
favouring development of highly virulent pathogens. At Finnish fish farms,
epidemics caused by opportunistic Flavobacterium columnare have been constantly
increasing in their prevalence and severity since the 1980’s. Yet, factors behind
the increased virulence of the pathogen and their mechanisms of action have
largely remained unsolved. In this thesis, I explore the effects of infection dose,
outside-host nutrients and coinfection with conspecific strains on virulence and
disease dynamics of F. columnare. Virulence of bacterial strains isolated from fish
farms was tested in experimental fish infections, where bacterial dose, water
nutrient concentration and number of infecting strains were manipulated. Two
fish species, zebra fish (Danio rerio) and rainbow trout (Oncorhynchus mykiss),
were used as hosts to confirm the suitability of zebra fish for further infection
experiments. Finally, strains isolated during 2003-2010 were studied for temporal
and local changes in their virulence, growth and competitive ability. Increase in
infection dose was found to increase bacterial virulence in both hosts. High
nutrient level increased virulence via enhanced bacterial growth and virulence
factor activation. I also found that coinfection can increase F. columnare virulence,
but the disease outcome depends on the strain characteristics. Finally, it is shown
that the aquaculture environment may select for strains with high virulence and
enhanced competitiveness. Taken together, the results indicate that all the
studied factors can contribute to opportunistic disease outbreaks in aquaculture.
...


Publisher
University of JyväskyläISBN
978-951-39-6818-2ISSN Search the Publication Forum
1456-9701Keywords
columnaris-tauti infektioannos yhteisinfektiot columnaris disease disease emergence fish farming Flavobacterium columnare opportunistic pathogen virulence virulence evolution kalataudit bakteeritaudit infektiotaudit infektiot taudinaiheuttajat bakteerit virulenssi ravinnepitoisuus kalanviljely kalanviljelylaitokset kirjolohi seeprakala
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