title: Low virulent infectious salmon anaemia virus (ISAV) replicates and initiates the immune response earlier than a highly virulent virus in Atlantic salmon gills.
abstract: Observations from the field and experimental evidence suggest that different strains of infectious salmon anaemia virus (ISAV) can induce disease of varying severity in Atlantic salmon. Variation in host mortality and dissemination of ISAV isolates with high and low virulence was investigated using immersion challenge; from which mortality, pathological, immunohistochemical and preliminary molecular results have been previously published. Here, real-time RT-PCR analysis and statistical modelling have been used to further investigate variation in virus load and the response of four select immune genes. Expression of type I and II interferon (IFN), Mx and γIFN induced protein (γIP) to high and low pathogenic virus infection were examined in gill, heart and anterior kidney. In addition, a novel RNA species-specific assay targeting individual RNA types was used to investigate the separate viral processes of transcription and replication. Unexpectedly, the low virulent ISAV (LVI) replicated and transcribed more rapidly in the gills compared to the highly virulent virus (HVI). Subsequently LVI was able to disseminate to the internal organs more quickly and induced a more rapid systemic immune response in the host that may have offered some protection. Contrary to this, HVI initially progressed more slowly in the gills resulting in a slower generalised infection. However HVI ultimately reached a higher viral load and induced a greater mortality.
authors.affiliation: Marine Scotland Science, Marine Laboratory, Aberdeen, Scotland, UK. alastair.mcbeath@scotland.gsi.gov.uk.
authors.forename: Alastair J A
authors.initials: AJ
authors.lastname: McBeath
authors.forename: Yee Mai
authors.initials: YM
authors.lastname: Ho
authors.forename: Maria
authors.initials: M
authors.lastname: Aamelfot
authors.forename: Malcolm
authors.initials: M
authors.lastname: Hall
authors.forename: Debes H
authors.initials: DH
authors.lastname: Christiansen
authors.forename: Turhan
authors.initials: T
authors.lastname: Markussen
authors.forename: Knut
authors.initials: K
authors.lastname: Falk
authors.forename: Iveta
authors.initials: I
authors.lastname: Matejusova
mesh_terms: D000818:Animals; D005393:Fish Diseases / Q000276:immunology* / Q000401:mortality / Q000821:virology*; D029941:Fish Proteins / Q000235:genetics* / Q000378:metabolism; D007150:Immunohistochemistry / Q000662:veterinary; D046829:Isavirus / Q000276:immunology / Q000472:pathogenicity* / Q000502:physiology*; D008962:Models, Theoretical; D008969:Molecular Sequence Data; D009928:Organ Specificity; D009976:Orthomyxoviridae Infections / Q000276:immunology / Q000401:mortality / Q000662:veterinary* / Q000821:virology; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D020317:Salmo salar; D017422:Sequence Analysis, DNA / Q000662:veterinary; D019562:Viral Load / Q000662:veterinary; D014774:Virulence; D014779:Virus Replication / Q000502:physiology
chemical_list: D029941:Fish Proteins