Phenotypic and genetic characterization of Piscirickettsia salmonis from Chilean and Canadian salmonids

Background. The study presents the phenotypic and genetic characterization of selected P. salmonis isolates from Atlantic salmon and rainbow trout suffering from SRS (salmonid rickettsial septicemia) in Chile and in Canada. The phenotypic characterization of the P. salmonis isolates were based on growth on different agar media (including a newly developed medium), different growth temperatures, antibiotics susceptibility and biochemical tests. Results. This is the first study differentiating Chilean P. salmonis isolates into two separate genetic groups. Genotyping, based on 16S rRNA-ITS and concatenated housekeeping genes grouped the selected isolates into two clades, constituted by the Chilean strains, while the Canadian isolates form a branch in the phylogenetic tree. The latter consisted of two isolates that were different in both genetic and phenotypic characteristics. The phylogenies and the MLST do not reflect the origin of the isolates with respect to host species. The isolates included were heterogeneous in phenotypic tests. Conclusions. The genotyping methods developed in this study provided a tool for separation of P. salmonis isolates into distinct clades. The SRS outbreaks in Chile are caused by minimum two different genetic groups of P. salmonis. This heterogeneity should be considered in future development of vaccines against this bacterium in Chile. Two different strains of P. salmonis, in regards to genetic and phenotypic characteristics, can occur in the same contemporary outbreak of SRS.publishedVersio

Vaksinering for forbedret immunitet og beskyttelse mot tenacibaculose hos atlantisk laks (ResisT)

Sårutvikling forårsaket av bakterielle infeksjoner på laks i sjø representerer et vedvarende problem for norsk lakseoppdrett. Sårutbrudd assosiert med Tenacibaculum finnmarkense (tenacibaculose) kjennetegnes ved sår på hodet, kjeven, inkludert finne- og haleråte og kan gi akutt dødelighet. Tenacibaculose er spesielt problematisk for nylig overført smolt, og det er ingen effektiv vaksine tilgjengelig. Prosjektet hadde som mål å undersøke effekten av å bruke rekombinante proteiner fra T. finnmarkense for å indusere beskyttelse mot sykdommen. Resultatene viser at immunisering ved injeksjon, men ikke nese- eller badeksponering, økte antistoffresponsen hos fisken. Vi utførte også smitteforsøk som bekreftet en beskyttende effekt med redusert dødelighet hos immunisert fisk. Disse funnene viser at rekombinant proteinteknologi er en mulig strategi for å utvikle en vaksine mot tenacibaculose i laksefisk.Vaksinering for forbedret immunitet og beskyttelse mot tenacibaculose hos atlantisk laks (ResisT)publishedVersio

Characterization of a VHS virus genotype III isolated from rainbow trout (Oncorhychus mykiss) at a marine site on the west coast of Norway

Background Norwegian production of rainbow trout (Oncorhynchus mykiss) has been without any outbreaks of VHS for many years until the disease emerged in a farm in western Norway in November 2007. The fish were, in addition to VHS virus, positive for gill chlamydia-like bacteria, Flavobacterium psychrophilum, and a microsporidian. A new VHS virus genotype III was isolated from the fish in RTgill-W1 cells and the complete coding region (11,065 nucleotides) was sequenced. This virus was also used in a challenge experiment to see if it could cause any mortality in rainbow trout in sea water. Results This is the first time a nearly complete sequence of a genotype III virus isolate has been presented. The organization of the genes is the same as in the other VHS virus genotypes studied (GI and GIV). Between the ORFs are nontranslated regions that contain highly conserved sequences encompassing the polyadenylation signal for one gene, and the putative transcription initiation site of the next gene. The intergenic regions vary in length from 74 nt to 128 nt. The nucleotide sequence is more similar to genotype I isolates compared to isolates from genotype II and IV. Analyses of the sequences of the N and G protein genes show that this new isolate is distinct from other VHS virus isolates and groups closely together with isolates from genotype III. In a challenge experiment, using intraperitoneal (ip) injection of the isolate, co-habitation with infected fish, and bath challenge, mortalities slightly above 40% were obtained. There was no significant difference in mortality between the bath challenged group and the ip injected group, while the mortality in the co-habitation group was as low as 30%. Conclusions All VHS virus isolates in genotype III are from marine fish in the North East Atlantic. Unlike the other known genotype III isolates, which are of low virulence, this new isolate is moderately virulent. It was not possible to detect any changes in the virus genome that could explain the higher virulence. A major problem for the study of virulence factors is the lack of information about other genotype III isolates

Characterization of a VHS virus genotype III isolated from rainbow trout (<it>Oncorhychus mykiss</it>) at a marine site on the west coast of Norway

Abstract Background Norwegian production of rainbow trout (Oncorhynchus mykiss) has been without any outbreaks of VHS for many years until the disease emerged in a farm in western Norway in November 2007. The fish were, in addition to VHS virus, positive for gill chlamydia-like bacteria, Flavobacterium psychrophilum, and a microsporidian. A new VHS virus genotype III was isolated from the fish in RTgill-W1 cells and the complete coding region (11,065 nucleotides) was sequenced. This virus was also used in a challenge experiment to see if it could cause any mortality in rainbow trout in sea water. Results This is the first time a nearly complete sequence of a genotype III virus isolate has been presented. The organization of the genes is the same as in the other VHS virus genotypes studied (GI and GIV). Between the ORFs are nontranslated regions that contain highly conserved sequences encompassing the polyadenylation signal for one gene, and the putative transcription initiation site of the next gene. The intergenic regions vary in length from 74 nt to 128 nt. The nucleotide sequence is more similar to genotype I isolates compared to isolates from genotype II and IV. Analyses of the sequences of the N and G protein genes show that this new isolate is distinct from other VHS virus isolates and groups closely together with isolates from genotype III. In a challenge experiment, using intraperitoneal (ip) injection of the isolate, co-habitation with infected fish, and bath challenge, mortalities slightly above 40% were obtained. There was no significant difference in mortality between the bath challenged group and the ip injected group, while the mortality in the co-habitation group was as low as 30%. Conclusions All VHS virus isolates in genotype III are from marine fish in the North East Atlantic. Unlike the other known genotype III isolates, which are of low virulence, this new isolate is moderately virulent. It was not possible to detect any changes in the virus genome that could explain the higher virulence. A major problem for the study of virulence factors is the lack of information about other genotype III isolates.</p

Genotyping of Tenacibaculum maritimum isolates from farmed Atlantic salmon in Western Canada

Mouthrot infections (bacterial stomatitis) have a significant impact on the Atlantic salmon aquaculture industry in Western Canada due to economic losses and fish welfare. Bacteria isolated from lesions in the field have been identified as Tenacibaculum maritimum. Mouthrot is different to classical tenacibaculosis, which is most commonly associated with ulcerative lesions, frayed fins and tail rot. The marine fish pathogen T. maritimum is found worldwide; however, in Western Canada, the knowledge of the genetic profile of T. maritimum is limited. This study looked at increasing this knowledge by genotyping T. maritimum isolates collected from Atlantic salmon from farms in Western Canada. These genotypes were compared to other species of the genus Tenacibaculum, as well as other known sequence types within the species. The Western Canadian isolates belong to two new sequence types within the T. maritimum species. Phylogenetic analysis shows that the isolates form a distinct branch together with T. maritimum NCIMB 2154T separate from other Tenacibaculum type strains, and they are most closely related to strains from Norway and Chile

Caligus rogercresseyi: posible vector en la transmisión horizontal del virus de la anemia infecciosa del salmón (ISAv)

Chile el año 2007 se convirtió en el segundo país productor de salmónidos a nivel mundial. Al año siguiente la industria salmonera nacional comenzó a experimentar una severa crisis sanitaria producida por el virus causante de la anemia infecciosa del salmón. Este virus se presentó por primera vez en Noruega (1984), luego en Canadá, Escocia, Islas Faroe, Estados Unidos y Chile (2007). La anemia infecciosa del salmón (ISA), es una enfermedad altamente contagiosa entre los peces, producida por un virus de la familia Orthomyxoviridae. La especie más vulnerable a este virus es el salmón del Atlántico (Salmo salar). La plaga parasitaria producida por el piojo de mar, Caligus rogercresseyi, copépodo ectoparásito, ha ido en aumento lo que favorece el contagio de enfermedades bacterianas y virales. De todas las especies cultivadas en Chile, el salmón del Atlántico, S. salar) es una de las especies más susceptibles de ser infestadas por C. rogercresseyi. Durante el 2006, la industria presentó un aumento significativo en las tasas de infestación por Caligus; luego en el 2007, aparecieron brotes del virus ISA. En Noruega, se ha demostrado que el piojo de mar, Lepeophtherius salmonis puede tener un rol como vector en la transmisión del virus ISA, por lo que el objetivo de este trabajo fue determinar si C. rogercresseyi es un vector de transmisión del virus ISA en el salmón del Atlántico, cultivado en el sur de Chile

Concurrent jellyfish blooms and tenacibaculosis outbreaks in Northern Norwegian Atlantic salmon (Salmo salar) farms

Tenacibaculosis is an increasing problem in the Norwegian Atlantic salmon aquaculture industry causing significant economic losses. In September 2015, two separate outbreaks of suspected tenacibaculosis occurred at two Atlantic salmon farms in Finnmark County in Northern Norway. The events resulted in major losses of smolts newly transferred into seawater. Prior to, and during the outbreaks, large numbers of small jellyfish, identified as Dipleurosoma typicum (Boeck) were observed in the vicinity of the farms and inside the net-pens. This study investigates the possible link between the jellyfish, Tenacibaculum spp. and the tenacibaculosis outbreaks. Bacteriology, histology, scanning and transmission electron microscopy, and real-time RT-PCR screening were performed on both fish and jellyfish samples. Based on the findings, Tenacibaculum finnmarkense was found to be the dominant bacteria associated with the tenacibaculosis outbreaks at both sites and that D. typicum is unlikely to be a vector for this fish pathogenic bacterium. However, results do show that the jellyfish caused direct damage to the fish’s skin and may have exacerbated the bacterial infection by allowing an entry point for bacteria