Abstract
Salmon gill poxvirus (SGPV) can cause serious gill disease in Atlantic salmon (Salmo salar L.) and represents a significant problem to aquaculture industries in Northern Europe. Here, a single-tube multi-locus variable-number tandem-repeat (VNTR) analysis (MLVA) genotyping assay, targeting eight VNTR loci, was developed for studying the epizootiology of SGPV. Through MLVA typing of SGPV positive samples from 180 farmed and wild Atlantic salmon in Northern Europe, the first molecular population study of this virus was undertaken. Comparison of resulting MLVA profiles by cluster analysis revealed considerable micro-diversity, while only a limited degree of specific clustering by country of origin could be observed, and no clustering relating to the severity of disease outbreaks. Phylogenetic analysis, based on genomic data from six SGPV specimens (three Norwegian, one Scottish, one Faroese and one Canadian), complemented and corroborated MLVA by pointing to a marked transatlantic divide in the species, with one main, relatively conserved, SGPV lineage as predominant in Europe. Within certain fjord systems and individual freshwater salmon smolt farms in Norway, however, discrete MLVA clustering patterns that prevailed over time were observed, likely reflecting local predominance of specific SGPV sub-lineages. MLVA typing was also used to refute two suspected instances of vertical SGPV transmission from salmon broodstock to offspring, and to confirm a failed disinfection attempt in one farm. These novel insights into the previously undocumented population structure of SGPV provide important clues, e.g., regarding the mechanisms underlying spread and recurrence of the virus amongst wild and farmed salmon populations, but so far no indications of more or less virulent SGPV sub-lineages have been found. The MLVA scheme represents a highly sensitive genotyping tool particularly well suited for illuminating SGPV infection routes, and adds to the relatively low number of MLVA protocols that have so far been published for viral species. Typing is reasonably inexpensive, with a moderate technological requirement, and may be completed within a single working day. Resulting MLVA profiles can be readily shared and compared across laboratories, facilitating rapid placement of samples in an international ezpizootiological context.
Highlights
While historic and ongoing expansions of industrialized aquaculture activities worldwide are among the most important initiatives for feeding a growing global population, these industries have suffered significant setbacks, e.g., due to infectious fish diseases
Barring available culturing methods for salmon gill poxvirus (SGPV), we developed a single-tube eight-locus Multi-locus variable-number tandem-repeat analysis (MLVA) assay that enables specific, high-resolution genotyping of this virus directly from infected gill tissue
Initial phylogenetic analysis verified a transatlantic genetic divide in this species, while MLVA typing and cluster analysis performed on samples from infected Atlantic salmon allowed interpretation of SGPV population dynamics in Europe
Summary
While historic and ongoing expansions of industrialized aquaculture activities worldwide are among the most important initiatives for feeding a growing global population, these industries have suffered significant setbacks, e.g., due to infectious fish diseases. In Norway, the world’s largest producer of farmed Atlantic salmon (Salmo salar L.), minimizing disease-related mortalities has been a priority, and farmed salmon today are routinely and efficiently vaccinated against an array of bacterial pathogens and a few viral agents (Brudeseth et al, 2013). The virus was named salmon gill poxvirus (SGPV), but another seven years, and the advent of next-generation sequencing, passed before a breakthrough was made in 2015 when the genome was sequenced (Gjessing et al, 2015). Its characterization enabled the development of novel diagnostic approaches, including qPCR assays and antibodies for immunohistochemistry, which in turn allowed confirmation of a close association between SGPV presence/localization and the typical gill pathology seen in disease outbreaks (Gjessing et al, 2015). A challenge model proving causality is currently under development (unpublished data)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
