Immune response modulation upon sequential heterogeneous co-infection with Tetracapsuloides bryosalmonae and VHSV in brown trout (Salmo trutta)

• Published in: Fish & shellfish immunology 2019-05, Vol.88, p.375-390
• Main Authors: Gorgoglione, Bartolomeo, Taylor, Nick G.H., Holland, Jason W., Feist, Stephen W., Secombes, Christopher J.
• Format: Article
• Language: English
• Subjects: Adaptive Immunity; Animals; Antimicrobial Peptides; Co-infections; Coinfection - immunology; Coinfection - parasitology; Coinfection - virology; Disease Models, Animal; Fish Diseases - immunology; Fish Diseases - parasitology; Fish Diseases - virology; Fish immunology; Gene Expression; Hemorrhagic Septicemia, Viral - immunology; Histopathology; Host-pathogen interaction; Immune response; Immunity, Innate; Interferon; Kidney Diseases - immunology; Kidney Diseases - veterinary; Myxozoa; Myxozoa - immunology; Oncorhynchus mykiss - immunology; Oncorhynchus mykiss - parasitology; Oncorhynchus mykiss - virology; Parasitic Diseases, Animal - immunology; Piscine Novirhabdovirus; Proliferative kidney disease; Real-Time Polymerase Chain Reaction; Response to pathogens; Salmonids; Th subsets; Th1 Cells - immunology
• ISSN: 1050-4648; 1095-9947
• DOI: 10.1016/j.fsi.2019.02.032

Simultaneous and sequential infections often occur in wild and farming environments. Despite growing awareness, co-infection studies are still very limited, mainly to a few well-established human models. European salmonids are susceptible to both Proliferative Kidney Disease (PKD), an endemic emergent disease caused by the myxozoan parasite Tetracapsuloides bryosalmonae, and Viral Haemorrhagic Septicaemia (VHS), an OIE notifiable listed disease caused by the Piscine Novirhabdovirus. No information is available as to how their immune system reacts when interacting with heterogeneous infections. A chronic (PKD) + acute (VHS) sequential co-infection model was established to assess if the responses elicited in co-infected fish are modulated, when compared to fish with single infections. Macro- and microscopic lesions were assessed after the challenge, and infection status confirmed by RT-qPCR analysis, enabling the identification of singly-infected and co-infected fish. A typical histophlogosis associated with histozoic extrasporogonic T. bryosalmonae was detected together with acute inflammation, haemorrhaging and necrosis due to the viral infection. The host immune response was measured in terms of key marker genes expression in kidney tissues. During T. bryosalmonae/VHSV-Ia co-infection, modulation of pro-inflammatory and antimicrobial peptide genes was strongly influenced by the viral infection, with a protracted inflammatory status, perhaps representing a negative side effect in these fish. Earlier activation of the cellular and humoral responses was detected in co-infected fish, with a more pronounced upregulation of Th1 and antiviral marker genes. These results reveal that some brown trout immune responses are enhanced or prolonged during PKD/VHS co-infection, relative to single infection. •First comprehensive transcriptional study on a sequential heterogeneous co-infection in fish.•Large primer set optimised for immune gene expression screenings in brown trout.•Significant correlations between pathogenesis and innate and adaptive immune genes expression.•Favourable modulations of T helper subsets activity seen in PKD/VHS co-infected fish.•Enhanced antiviral response seen in PKD/VHS co-infected fish.