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).