No Evidence of the Vertical Transmission of Non-Virulent Infectious Salmon Anaemia Virus (ISAV-HPR0) in Farmed Atlantic Salmon

Abstract

The nonvirulent infectious salmon anaemia virus (ISAV-HPR0) is the putative progenitor for virulent-ISAV, and a potential risk factor for the development of infectious salmon anaemia (ISA). Understanding the transmission dynamics of ISAV-HPR0 is fundamental to proper management and mitigation strategies. Here, we demonstrate that ISAV-HPR0 causes prevalent and transient infections in all three production stages of Atlantic salmon in the Faroe Islands. Phylogenetic analysis of the haemagglutinin-esterase gene from 247 salmon showed a clear geographical structuring into two significantly distinct HPR0-subgroups, which were designated G2 and G4. Whereas G2 and G4 co-circulated in marine farms, Faroese broodfish were predominantly infected by G2, and smolt were predominantly infected by G4. This infection pattern was confirmed by our G2- and G4-specific RT-qPCR assays. Moreover, the HPR0 variants detected in Icelandic and Norwegian broodfish were never detected in the Faroe Islands, despite the extensive import of ova from both countries. Accordingly, the vertical transmission of HPR0 from broodfish to progeny is uncommon. Phylogenetic and statistical analysis suggest that HPR0 persists in the smolt farms as “house-strains”, and that new HPR0 variants are occasionally introduced from the marine environment, probably by HPR0-contaminated sea-spray. Thus, high biosecurity—including water and air intake—is required to avoid the introduction of pathogens to the smolt farms.

Infection-induced increases to population size during cycles in a discrete-time epidemic model

“… 2019 ; Christiansen et al. 2021 ). An argument for the reduction in reproductive output is based on the proposal that fish viruses which influence female health may alter fecundity through the production of lower quality of eggs and reduced hatchling survival (Kane-Sutton et al.…”

Development and application of a whole genome amplicon sequencing method for infectious salmon anemia virus (ISAV)

“…The disease can cause serious fish welfare problems and also cause large financial losses for the fishing industry. Governmental control measures include containment of infected fish farms, restrictions on future farming, or eradication of all types of fish in infected pens (Christiansen et al, 2021 ). Infection with the pathogenic variant of ISA virus (ISAV) is listed in category C+D+E by the EU Regulation 2018/1882 (The European Commission, 2018 ) and as a notifiable disease by the World Organisation for Animal Health ( 2023 ).…”