title: Transcriptional immune response of cage-cultured Pacific bluefin tuna during infection by two Cardicola blood fluke species.
abstract: Infections by two blood fluke species, Cardicola orientalis and Cardicola opisthorchis, currently present the greatest disease concern for the sea-cage culture of Pacific bluefin tuna (PBT) - a species of high global economic importance and ecological concern. In this study, we aimed to rapidly, quantitatively, and differentially identify infections by these two parasite species in cultured PBT as well as identify potential host immune responses. Using real-time qPCR, we were successful in quantitatively detecting parasite-specific DNA from within host blood, gill, and heart tissues; positively identifying parasitic infections 44 days earlier than microscopy methods previously employed. Both gill and heart became heavily infected by both parasite species in PBT within two months of sea-cage culture, which was only mitigated by the administration of anthelmintic praziquantel. Nevertheless, fish were observed to mount an organ specific transcriptive immune response during infection that mirrored the relative quantity of pathogenic load. In heart, significant (3-6 fold) increases in IgM, MHC2, TCRβ, and IL-8 transcription was observed in infected fish relative to uninfected controls; whereas in the gills only IgM transcription was observed to be induced (11 fold) by infection. Interestingly, the relative quantity of IgM transcription was highly correlated to the relative abundance of C. orientalis but not C. opisthorchis DNA in the gill samples, even though this organ showed high prevalence of DNA from both parasite species. Taken together, these findings indicate that although ineffective at combating infection during primary exposure, a cellular immune response is mounted in PBT as a potential rejoinder to future Cardicola exposure, particularly against C. orientalis. Although future investigation into antibody effectiveness will be needed, this work provides valuable preliminary insight into host responsiveness to Cardicola infection as well as additional support for the need of anthelmintic treatment following primary parasite exposure during PBT culture.
authors.affiliation: National Centre for Marine Conservation and Resource Sustainability, Australian Maritime College, University of Tasmania, Launceston, Tasmania, Australia. Electronic address: mark.polinski@utas.edu.au.
authors.forename: Mark
authors.initials: M
authors.lastname: Polinski
authors.affiliation: Fisheries Laboratory, Kinki University, Nishimuro, Wakayama, Japan.
authors.forename: Sho
authors.initials: S
authors.lastname: Shirakashi
authors.affiliation: National Centre for Marine Conservation and Resource Sustainability, Australian Maritime College, University of Tasmania, Launceston, Tasmania, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Bridle
authors.affiliation: National Centre for Marine Conservation and Resource Sustainability, Australian Maritime College, University of Tasmania, Launceston, Tasmania, Australia.
authors.forename: Barbara
authors.initials: B
authors.lastname: Nowak
mesh_terms: D000818:Animals; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics; D005393:Fish Diseases / Q000097:blood / Q000276:immunology / Q000469:parasitology*; D019674:Genes, T-Cell Receptor beta / Q000235:genetics / Q000276:immunology; D005880:Gills / Q000469:parasitology; D006321:Heart / Q000469:parasitology; D007075:Immunoglobulin M / Q000235:genetics / Q000276:immunology; D016209:Interleukin-8 / Q000235:genetics / Q000276:immunology; D018510:RNA, Helminth / Q000737:chemistry / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D018709:Statistics, Nonparametric; D014158:Transcription, Genetic / Q000276:immunology*; D014200:Trematoda / Q000235:genetics / Q000276:immunology*; D014201:Trematode Infections / Q000097:blood / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*; D014413:Tuna
chemical_list: D021903:DNA, Ribosomal Spacer; D007075:Immunoglobulin M; D016209:Interleukin-8; D018510:RNA, Helminth
keywords: Cardicola; Pacific bluefin tuna; Quantitative detection; Transcriptional immune response