Atlantic salmon adapted to seawater for 9 weeks develop a robust immune response to salmonid alphavirus upon bath challenge. Issue 74 (March 2018)

• Record Type: Journal Article
• Authors: Moore, L.J.; Jarungsriapisit, J.; Nilsen, T.O.; Stefansson, S.; Taranger, G.L.; Secombes, C.J.; Morton, H.C.; Patel, S.
• Is Part Of: Fish & shellfish immunology. Issue 74(2018)
• Page Start: 573
• Page End: 583
• Publication Date: 2018-03
• Subjects: Salmo salar -- Salmonid alphavirus -- Inflammation -- Gene transcription -- Bath immersion -- Smoltification -- Seawater transfer -- Post-smolt -- SAV; Fishes -- Immunology -- Periodicals; Shellfish -- Immunology -- Periodicals; Poissons -- Immunologie -- Périodiques; Crustacés -- Immunologie -- Périodiques; 571.9617
• DOI: 10.1016/j.fsi.2017.12.017
• Languages: English
• ISSNs: 1050-4648

Abstract

Abstract: Pancreas disease (PD) caused by salmonid alphavirus (SAV) is the most serious viral disease in Norwegian aquaculture. Study of the immune response to SAV will aid preventative measures including vaccine development. The innate immune response was studied in Atlantic salmon infected by either bath immersion (BI) or by intra-muscular ( i.m. ) injection (IM) with SAV subtype 3, two and nine weeks after seawater transfer (Phases A and B respectively). Phase A results have been previously published (Moore et al., 2017) and Phase B results are presented here together with a comparison of results achieved in Phase A. There was a rapid accumulation of infected fish in the IM-B (IM Phase B) group and all fish sampled were SAV RNA positive by 7 dpi (days post infection). In contrast, only a few SAV RNA positive (infected) fish were identified at 14, 21 and 28 dpi in the BI-B (BI Phase B) group. Differences in the transcription of several immune genes were apparent when compared between the infected fish in the IM-B and BI-B groups. Transcription of the analysed genes peaked at 7 dpi in the IM-B group and at 14 dpi in the BI-B group. However, this latter finding was difficult to interpret due to the low prevalence of SAV positive fish in this group. Additionally, fish positive for SAV RNA in the BI-B group showed higher transcription of IL-1β, IFNγ and CXCL11_L1, all genes associated with the inflammatory response, compared to the IM-B group. Histopathological changes in the heart were restricted to the IM-B group, while (immune) cell filtration into the pancreas was observed in both groups. Compared to the Phase A fish that were exposed to SAV3 two weeks after seawater transfer, the Phase B fish in the current paper, showed a higher and more sustained innate immune gene transcription in response to the SAV3 infection. In addition, the basal transcription of several innate immune genes in non-infected control fish in Phase B (CT-B) was also significantly different when compared to Phase A control fish (CT-A). Highlights: Salmon adapted to seawater for a longer time have a higher and longer interferon response to SAV. Immune response after bath challenge follows that for a i.m. challenge in fish transferred to seawater 9 weeks earlier. Non-infected control fish have higher basal levels of several immune genes when adapted for a longer time in seawater. After 9 weeks in seawater salmon can maintain a good immune response for a longer period.