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Molecular detection systems for bacterial and viral fish pathogens

Classical methods such as bacteriology are not capable of identifying the majority of fish pathogens unless there are significant numbers of pathogen present in the sample. Typically, this means that the samples are from farms where signs of disease are already apparent to management. Lack of selective media, pathogens that are non-cultivatable, and poor sensitivity mean it is impossible to detect the lower numbers of pathogen present when no signs of disease are apparent. Therefore, generation of data on pathogen ecology and occurrence and progression of disease, which would greatly improve farm management strategies on disease control and prevention, is extremely difficult if not unfeasible.
Molecular based detection systems such as deoxyribonucleic acid (DNA) probes and enzyme linked immunosorbent assay (ELISA) techniques with their inherent ability to recognise very low numbers of pathogen, and with no requirement to culture pathogen, represent a logical solution to these problems. DNA probe-PCR tests and ELISA tests were developed for 4 species of fish pathogen: Aeromonas salmonicida; Yersinia ruckerii; Vibrio vulnificus; and infectious pancreatic necrosis virus. The sensitivity and specificity of each test was evaluated. Procedures were described to sample both fish tissues and non fish samples including farm waters and sediments. The results show that it was possible to use both DNA probe and ELISA tests to detect pathogen in farm samples when no signs of clinical infection were obvious and when bacteriology proved fruitless. In these cases pathogen detection correlated with subsequent clinical disease among farm fish stocks. In summary, these molecular detection systems have the potential to be useful monitoring tools for fish farm management to aid their strategies on disease control.

Reported by

University College Galway
Galway
Ireland
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