Vaccination Against Furunculosis

The term furunculosis is used to describe a lethal septicemia of salmonid species caused by the bacterium Aeromonas salmonicida subsp. salmonicida, but can also denote infections with atypical strains of the furunculosis bacterium occurring in a broad range of freshwater and marine species and most frequently manifesting with severe skin ulceration and wounds. The classical furunculosis bacterium (subsp. salmonicida) shows a remarkable genotypic and phenotypic uniformity worldwide, while the atypical A. salmonicida strains are much more diverse. Both classical and atypical furunculosis isolates possess a variety of cellular and extracellular pathogenicity and virulence factors that have been intensively studied over several decades. In general, none of these factors have proven alone responsible for the bacterium's ability to infect the host and cause mortality. Research to rank the protective antigens for both classical and atypical furunculosis bacteria has yielded inconsistent and apparently contradictory results, but evidence is accumulating to suggest that presence of the A-layer is perhaps the most important among the antigenic factors. Injectable, oil-adjuvanted vaccines against classical furunculosis are licensed in the largest salmonid farming markets, and frequently come in combination with other bacterial and viral antigens, while vaccines for immersion or oral administration, or live vaccine concepts have not been successful so far. Although classical furunculosis may provide some cross-protection, vaccines against atypical furunculosis need to be prepared with bacterial strains that are specific to the species and/or to the region in question, using oil-adjuvant technology.