Loma salmonae in Chinook salmon (Oncorhynchus tshawytscha): improving detection, preventing infection, and increasing our understanding of the host response to a microsporidian parasite




Thomson, Catherine Ann

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Loma salmonae is a microsporidian parasite that infects economically important Chinook salmon (Oncorhynchus tshawytscha) farmed in British Columbia, Canada. Here a variety of research efforts aimed at improving early detection and diagnostic tools, developing preventative strategies, and increasing understanding of the parasite/host interactions are presented. First, the development of chicken-derived polyclonal antibodies (IgY) specific for L. salmonae is described. These antibodies have proven useful for immunohistochemical detection of parasites very early in the infection process. Next, the immune-modulating effects of intra-peritoneal β-glucan inoculation of Chinook salmon are presented. Intensity of L. salmonae infection was significantly reduced in fish inoculated with β-glucan 3 weeks prior to parasite exposure, although prevalence was not reduced in these fish. Gene expression analysis of head kidney from glucan-inoculated fish measured at 1, 2 and 3 weeks post-inoculation (PI) revealed that the majority of differential expression occurred at 1 week. Pathways related to antioxidant defence, innate immune responses, antigen presentation, as well as oxidative metabolism were up-regulated in glucan-inoculated fish at 1 week PI. Finally, temporal gene-expression analysis on gill and kidney tissue from Chinook salmon infected with L. salmonae is described. Analysis at 4 weeks post-exposure (PE) in the gill revealed an early up-regulation of gas transport, whereas numerous pathways including oxidative metabolism, antioxidant defences, monooxygenases and immune receptors were down-regulated in the gill at the same time point. Similarly, oxidative metabolism, antioxidant defences, and monooxygenases were down-regulated in the kidney at 4 weeks PE. However, there is evidence for a developing immune response over time. Antigen processing and presentation pathways were up-regulated in the kidney at 4 weeks and in both tissues at 8 weeks PE. In addition a number of immune receptors and genes involved with innate immune functions were also up-regulated at 4 and 8 weeks PE in the kidney.



Chinook salmon, Fishes, Parasites