Genetically modified attenuated salmonid alphavirus: A potential strategy for immunization of Atlantic salmon

Abstract

Pancreas disease (PD) is a serious challenge in European salmonid aquaculture caused by salmonid alphavirus (SAV). In this study, we report the effect of immunization of Atlantic salmon with three attenuated infectious SAV3 strains with targeted mutations in a glycosylation site of the envelope E2 protein and/or in a nuclear localization signal in the capsid protein. In a pilot experiment, it was shown that the mutated viral strains replicated in fish, transmitted to naïve cohabitants and that the transmission had not altered the sequences. In the main experiment, the fish were immunized with the strains and challenged with SAV3 eight weeks after immunization. Immunization resulted in infection both in injected fish and 2 weeks later in the cohabitant fish, followed by a persistent but declining load of the mutated virus variants in the hearts. The immunized fish developed clinical signs and pathology consistent with PD prior to challenge. However, fish injected with the virus mutated in both E2 and capsid showed little clinical signs and had higher average weight gain than the groups immunized with the single mutated variants. The SAV strain used for challenge was not detected in the immunized fish indicating that these fish were protected against superinfection with SAV during the 12 weeks of the experiment.

Triploid Atlantic salmon (Salmo salar) may have increased risk of primary field outbreaks of infectious salmon anaemia

“…To estimate the level of viral RNA and relative expression of immune response genes, RT‐qPCR was run using samples from six fish from each group from each sampling. Total RNA was extracted from 30–40 mg heart and kidney tissue using the RNeasy Mini kit and QIAcube System (Qiagen) as described earlier (Aksnes et al, 2021 ). The concentration of RNA was determined by spectrophotometry using the Nanodrop ND1000 (Nanodrop Technologies, Wilmington, USA).…”

Current status and development prospects of aquatic vaccines

“…In veterinary medicine, there are three types of live vaccines: strong, weak, and heterologous vaccines ( 41 ). Live aquatic vaccines are now more commonly used with pathogenic strains that have been weakened or mutated, such as the F25 ( 9 ) antipyretic strain of viral hemorrhagic septicemia virus (VHSV), infectious spleen and kidney necrosis virus (ISKNV), attenuated channel catfish virus (CCV) vaccine, attenuated Furunculosis vaccine, attenuated haematopoietic necrosis virus (IHNV) vaccine ( 42 – 47 ). The outstanding benefit of live vaccines is that the pathogen replicates in the host to produce antigenic stimuli, and the quantity, type, and location of these antigens are similar to those of natural infections.…”