Molecular Detection and Characterization of Furunculosis and Other Aeromonas Fish Infections

Species of the genus Aeromonas, which inhabit aquatic environments, can produce septicaemia and ulcerative and hemorrhagic fish diseases, including furunculosis, which result in mass death and important economic losses in the aquaculture sector (Austin & Austin, 2007; Beaz-Hidalgo et al., 2010; Bernoth et al., 1997; Gudmundsdóttir & Björnsdóttir, 2007; Noga, 2010; Wiklund & Dalsgaard, 1998). The species Aeromonas salmonicida (with 5 subspecies: salmonicida, masoucida, smithia, achromogenes and pectinolytica) and Aeromonas hydrophila have classically been considered the most important Aeromonas fish pathogens, and the subspecies salmonicida is thought to be the causal agent of furunculosis, a disease that was reported more than a century ago to affect trout, and later to affect other salmonids and fish species (Bernoth et al., 1997; Goodwin & Merry, 2009; Han et al., 2011; Noga, 2010; Wiklund & Dalsgaard, 1998). Nowadays, furunculosis has a worldwide distribution, having been reported in Scotland, France, Norway, Iceland, Spain, United States, Canada, Japan, Chile and Australia. The fact that many strains isolated from diseased fish do not fit the described characteristics defined for A. salmonicida subsp. salmonicida or for furunculosis has lead to the terms ‘atypical strains’ and ‘atypical furunculosis’ to be introduced when they are attributed to other A. salmonicida subspecies, other Aeromonas species or when furunculosis occurs in fish other than salmonids (Wiklund & Dalsgaard, 1998). This causes confusion because the term ‘atypical’ is applied in different ways by the authors.