Detection of covert Aeromonas salmonicida infection in Atlantic salmon and other salmonids

During the early 1900s, several researchers cultured Aeromonas salmonicida, cause of furunculosis disease, from the kidneys and intestines of apparently healthy trout. Home (1928) speculated that asymptomatic carriers become reservoirs of infection. Hence, a need was perceived for bacteriological examinations to be conducted even before asymptoimatic fish were stocked. During the devastating outbreaks of furunculosis that occurred in Great Britain in the 1920-30s, Mackie et al. (1933) noted that epizootics in natural waters correlated with the stocking of fish originating from infected farms. They also noted that the kidney was the usual site of harborage of the pathogen but culture often provided inadequate detection. More recent studies continue to emphasize the importance of asymptomatic, carrier fish as reservoirs of infection and spread of the disease within the natural environment (Jarp et al. 1993, Johnsen and Jensen 1994).