Protecting the salmonids
Infectious agents are the key causes for the major fish disease problems in cultures of salmonid stocks, such as the salmon and trout. As such the Renibacterium salmmoninarum is the BKD causal agent leading to significant losses, mortality figures in the range between 60%-80%. The currently employed immunisation methodologies involve the injection of serum coming from salmonids exposed to but unaffected by BKD. However, this immunisation approach has been proven effective only for weakening the disease's harmfulness and delaying mortality. Despite this, it has also been observed that there is a latency period of several weeks between the introduction of the BKD bacterial and the fish's death. Thus, the serum may be seriously affected from virulence factors that render this passive immunisation method impotent to control full resistance to the disease. In response to this finding, this project conducted research studies for selecting suitable protective antigens for extending the serum's preservation under these hostile conditions. The use of fermentation approaches with proper alteration of the conditions for developing Renibacterium stimulated the expression of virulence factors. As a result three proteins were selected, further studied, cloned and in vivo tested when the rainbow trout was experimentally infected with Renibacterium cells. The gene encoding for these antigens expressed in bacteria was used for producing two vaccines that were found to be very effective when injected. The BKD disease, which is a difficult disease to control, could now be limited through the use of appropriate treatments. In addition, the research work resulted in the development of a complete genomic library of Renibacterium salmoninarum, a valuable tool for fish culturists, biologistists, fisheries managers and researchers.
