Summary auto-generated
This study reports the first successful propagation of infectious salmon anaemia virus (ISAV) in an established commercial fish cell line—the Atlantic salmon (AS) cell line. ISAV, which causes severe anaemia and high mortality in farmed Atlantic salmon, had previously only been isolated in primary cell cultures. The researchers grew ISAV in AS cells with and without trypsin treatment and measured viral yield through infectivity trials in live salmon. Viral yield increased over 11 days of culture without requiring trypsin treatment. The infection was non-cytopathic but could be detected using a novel haemadsorption centre assay with Atlantic salmon erythrocytes. Electron microscopy revealed pleomorphic enveloped virus particles (90–130 nm diameter) with surface spikes. Biochemical inhibitor studies showed that ISAV replication was blocked by actinomycin D but not by the DNA synthesis inhibitor 5-bromo-2-deoxyuridine, indicating an RNA genome. Based on morphology, haemadsorbing ability, and inhibitor sensitivity, the authors propose that ISAV is likely an aquatic orthomyxovirus with unusually low optimal growth temperature.
Key findings
- ISAV was successfully propagated for the first time in an established commercial fish cell line (Atlantic salmon cells), with infectious yield increasing over 11 days of culture
- Trypsin treatment was not required for ISAV infection and replication of AS cells, suggesting salmon-grown virus contains fully cleaved spike proteins
- A haemadsorption centre assay using Atlantic salmon erythrocytes was developed to detect and quantify non-cytopathic ISAV infection in cell culture
- Biochemical studies indicated ISAV has an RNA genome and shows sensitivity to actinomycin D, supporting classification as an aquatic orthomyxovirus
- Electron microscopy revealed 90–130 nm pleomorphic enveloped particles with characteristic surface spikes and organized nucleocapsid structure
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Abstract
Infectious salmon anaemia virus (ISAV), which previously had never been isolated in any of the commercially available established fish cell lines, was successfully propagated in the continuous cell line Atlantic salmon (AS). The yield of infectious ISAV increased with the incubation time of virus-inoculated cells, demonstrated by in vivo infectivity trials in groups of Atlantic salmon. Trypsin treatment of the virus was not necessary for primary infection of AS cells with salmon-grown ISAV. The infection was non-cytopathic, but it was possible to detect virus- infected cells by a haemadsorption centre assay using Atlantic salmon erythrocytes. Pleomorphic enveloped virus particles were seen by transmission electron microscopy of infected AS cells. Elongated forms were observed, but spherical particles with diameters of 90-130 nm were commonest. Growth of ISAV was inhibited by actinomycin D but not by 5- bromo-2-deoxyuridine treatment, which indicates that ISAV may be an aquatic orthomyxovirus.