Tissue tropism and non-lethal detection of Nucleospora cyclopteri (Microsporidia) in lumpfish (Cyclopterus lumpus L.)
Master thesis
Permanent lenke
https://hdl.handle.net/1956/18060Utgivelsesdato
2018-06-13Metadata
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Sammendrag
In the present study, wild-caught mature lumpfish (Cyclopterus lumpus) from a brood fish fishery in Norway were examined for the microsporidian parasite Nucleospora cyclopteri. This was done in order to reveal the tissue tropism of the parasite and to establish non-lethal sampling methods for detection. This effort will be important for establishing N. cyclopteri-free brood stock. The parasite may be vertically transmitted and have immunosuppressive effects on the host and could be important for reducing the mortalities of lumpfish in sea pens. This is essential for optimizing the use of cleaner fish with salmon and thus reducing the numbers of salmon louse in the sea. Nucleospora cyclopteri has caused several instances of disease in both wild and farmed lumpfish (Mullins et al., 1994; Freeman et al., 2013; Alarcon et al., 2016). The parasite has been observed in the nuclei of lymphocytes or lymphoblasts (Mullins et al., 1994; Freeman et al., 2013), and may stimulate an unusual proliferation of these leukocytes (Karlsbakk et al., 2014). Lumpfish heavily infected with N. cyclopteri show characteristically enlarged kidneys with pale patches or nodules (Mullins et al., 1994; Freeman et al., 2013; Freeman & Kristmundsson, 2013; Karlsbakk et al., 2014; Alarcon et al., 2016). The parasite has previously been detected in kidney, heart, spleen, skin, gills and eggs of lumpfish using nested PCR (Freeman et al., 2013; Alarcon et al., 2016). In the present study, the parasite density in different tissues were quantified in order to examine the tissue distribution of the parasite. Nucleospora cyclopteri was detected in all nine tissues examined: anterior-, mid- and posterior kidney, spleen, heart, gills, brain, muscle, liver and blood. This supports that the infection may be systemic, as previously suggested. Densities of N. cyclopteri were highest in anterior kidney, followed by mid and posterior kidney, spleen, heart and gills. The highest variation of parasite densities was detected in the anterior kidney, and this might be related to more extensive parasite proliferation at this site. Urine were positive for N. cyclopteri and spores were detected in kidney smears, indicating possible shedding of the parasite from the host kidney via urine. It is also demonstrated that the parasite can be detected using skin, gill and vent swabs, blood samples and gill biopsies, and thus showing the possibility of non-lethal detection in lumpfish. The most promising non-lethal samples for detection were gill biopsies and leukocyte fractions from blood samples. Further work should be conducted in order to improve these detection methods further.