Parasite vs. host: Molecular responses in sea lice infecting immunostimulated Atlantic salmon
Sea lice (or salmon lice) are small parasitic marine invertebrates that attach and feed on the external surfaces of wild and farmed fish. Although infections occur naturally and salmon have many natural defenses against this parasite, in some cases infections can cause major damage. These parasites have been an issue for farmed Atlantic salmon globally; without intervention Atlantic salmon can be infected by high numbers of lice. Intervention to remove lice can be conducted several ways, but the most typical is by adding compounds to the fish feed that cause the lice to fall off of the salmon host. Problematically, these compounds are becoming less and less effective as parasites are becoming resistant to their effects.
New control methods against sea lice are therefore required, possibly in combination with existing treatments. Atlantic salmon are known to be more susceptible to lice infections than other salmonid species and therefore can be infected at high levels. In this work, we stimulated the immune system of farmed Atlantic salmon by feeding fish food containing immunostimulants to produce an Atlantic salmon immune response that is more similar to other salmon species that are more resistant to lice (e.g., pink salmon). We demonstrated that the host immune system is stimulated by the feed by profiling levels of specific inflammatory markers in immunostimulant-fed salmon and those fed a control diet without immunostimulants. We found that the immunostimulant-fed salmon hosts have lower levels of infecting lice than the hosts fed a control diet.
An additional and ongoing goal of our research is to improve our understanding of the inner mechanisms of lice responses to different hosts (susceptible or resistant to lice infection). In this project, we also profiled the response of the lice to this stimulated Atlantic salmon relative to the control Atlantic salmon. We found genes being over- and under-expressed in the lice feeding on immunostimulated salmon, which may provide us with information on how lice handle a more effectively responding host. The more we know about the way a louse handles these various hosts at the genomic and physiological level the better we can predict how host-resistance may interact with other parasite stressors to have effects on louse survival and development.
Read the full paper — Host–parasite transcriptomics during immunostimulant-enhanced rejection of salmon lice (Lepeophtheirus salmonis) by Atlantic salmon (Salmo salar) by Ben J.G. Sutherland, Jennifer M. Covello, Sarah E. Friend, Jordan D. Poley, Kim W. Koczka, Sara L. Purcell, Tara L. MacLeod, Bridget R. Donovan, Jorge Pino, Jose Luis González-Vecino, et al. on the FACETS website.
