Characterization of piscine orthoreovirus-1 attachment to salmonid erythrocytes

Introduction: Piscine orthoreovirus-1 (PRV-1) is the causative agent of heart and skeletal muscle inflammation (HSMI), an important disease in Atlantic salmon aquaculture. The main target cells for PRV-1 are erythrocytes, which in fish are nucleated cells that support viral replication. In an ongoing study, we are working to characterize the attachment of PRV to salmonid erythrocytes. Methodology: We have developed an ex vivo assay in which high-titer PRV from plasma samples of fish is adsorbed to erythrocytes isolated from Atlantic salmon blood samples. Viral attachment to the cell surface is monitored by flow cytometric detection of PRV sigma 1 protein. Results and conclusion: The virus binds to all erythrocytes and is present on the cell surface after only 5 minutes of incubation time. Binding is significantly reduced by preincubation of the virus with antibodies specific for sigma 1, indicating that sigma 1 is required for binding. Pretreatment of cells with wheat germ agglutinin (WGA) does not interfere with virus adsorption, suggesting that sialic acid does not contribute to attachment. Binding also appears to be specific to Atlantic salmon erythrocytes, as the virus does not adsorb to erythrocytes from other salmonid species such as rainbow trout. No difference in binding is observed between PRV-1 variants of high and low virulence. The goal of this project is to identify receptors used by PRV-1 to enter erythrocytes. Such knowledge will provide valuable insights for both vaccine development and selective breeding, which may reduce the prevalence of HSMI in Atlantic salmon aquaculture.