First report of a rickettsia-like organism from farmed Chinook salmon, <i>Oncorhynchus tshawytscha</i> (Walbaum), in New Zealand

A Piscirickettsia salmonis infection was diagnosed in lumpfish (Cyclopterus lumpus L.) juveniles held in a marine research facility on the west coast of Ireland. The main clinical signs and pathology included marked ascites, severe multifocal liver necrosis and severe diffuse inflammation and necrosis of the exocrine pancreas and peri-pancreatic adipose tissue. Numerous Piscirickettsia-like organisms were observed by histopathology in the affected organs, and the bacterial species was characterized by molecular analysis. Sequencing of the partial 16S rDNA gene and internal transcribed spacer region showed the lumpfish sequences to be closely related to previously identified Atlantic salmon (Salmo salar L.) sequences from Ireland. To the authors' knowledge, this is the first detection of P. salmonis in lumpfish worldwide. The infection is considered potentially significant in terms of lumpfish health and biosecurity.

Section: Discussionmentioning

confidence: 97%

Piscirickettsia salmonis infection in cultured lumpfish (Cyclopterus lumpus L.)

Marcos-López¹,

Ruane

Scholz³

et al. 2017

“…Fish ( n = 153) were collected from three growing sites in the Marlborough Sounds (sites 1–3). Site 1 was the location of initial detection of NZ‐RLO and T. maritimum in 2015 (Brosnahan et al., ). Fish were sampled twice over 1 year from site 1, five times over 3 years from site 2 and once from site 3 (Table ).…”

Section: Methodsmentioning

confidence: 99%

“…A published real‐time PCR targeting the 23S rRNA gene of P. salmonis (Corbeil, McColl, & Crane, ) was carried out with modifications as previously described (Brosnahan et al., ). All samples were tested in duplicate with a high and low DNA template concentration, 1 μl and 3 μl, to maximize the likelihood of detecting organisms at different concentrations within the tissue.…”

Section: Methodsmentioning

confidence: 99%

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New Zealand rickettsia‐like organism (NZ‐RLO) and Tenacibaculum maritimum: Distribution and phylogeny in farmed Chinook salmon (Oncorhynchus tshawytscha)

Brosnahan

Munday

et al. 2018

A total of 777 fish from three growing regions of New Zealand Chinook salmon farms comprising of five sites were tested. Quantitative PCR was used to determine the distribution of New Zealand rickettsia‐like organism and Tenacibaculum maritimum. Genetic information from these bacteria were then compared with strains reported worldwide. Using this information, suggested associations of pathogens with clinically affected fish were made. NZ‐RLO was detected in two of the three regions, and T. maritimum was detected in all regions. Three strains of NZ‐RLO were identified during this study. Based on analysis of the ITS rRNA gene, NZ‐RLO1 appears to be part of an Australasian grouping sharing high similarity with the Tasmanian RLO, NZ‐RLO2 was shown to be the same as an Irish strain, and NZ‐RLO3 was shown be closely related to two strains from Chile. Based on multi‐locus sequence typing, the New Zealand T. maritimum was the same as Australian strains. NZ‐RLOs were detected more frequently in fish with skin ulcers than fish without skin ulcers. While additional research is required to investigate the pathogenicity of these organisms, this is the first time that NZ‐RLOs have been associated with the development of clinical infections in farmed Chinook salmon.

“…The first New Zealand RLO, designated New Zealand rickettsia‐like organism (NZ‐RLO), was isolated from farms in the South Island and found to be identical to the TAS‐RLO based on the nucleotide identity comparison of the partial 16S rDNA and partial ITS genes (Brosnahan, Ha, Booth, McFadden, & Jones, ; Gias et al., ). A second RLO isolated from the same farm showed highest nucleotide identity to the partial ITS gene (100%) and partial 16S rRNA (99%) of P. salmonis isolate IRE‐99C (GenBank accession ) and P. salmonis isolate IRE‐99D (GenBank accession ), respectively.…”

Section: Introductionmentioning

confidence: 99%

In vivo growth and genomic characterization of rickettsia‐like organisms isolated from farmed Chinook salmon (Oncorhynchus tshawytscha) in New Zealand

Gias

Brosnahan

Orr

et al. 2018

A rickettsia-like organism, designated NZ-RLO2, was isolated from Chinook salmon (Oncorhynchus tshawytscha) farmed in the South Island, New Zealand. In vivo growth showed NZ-RLO2 was able to grow in CHSE-214, EPC, BHK-21, C6/36 and Sf21 cell lines, while Piscirickettsia salmonis LF-89 grew in all but BHK-21 and Sf21. NZ-RLO2 grew optimally in EPC at 15°C, CHSE-214 and EPC at 18°C. The growth of LF-89 was optimal at 15°C, 18°C and 22°C in CHSE-24, but appeared less efficient in EPC cells at all temperatures. Pan-genome comparison of predicted proteomes shows that available Chilean strains of P. salmonis grouped into two clusters (p-value = 94%). NZ-RLO2 was genetically different from previously described NZ-RLO1, and both strains grouped separately from the Chilean strains in one of the two clusters (p-value = 88%), but were closely related to each other. TaqMan and Sybr Green real-time PCR targeting RNA polymerase (rpoB) and DNA primase (dnaG), respectively, were developed to detect NZ-RLO2. This study indicates that the New Zealand strains showed a closer genetic relationship to one of the Chilean P. salmonis clusters; however, more Piscirickettsia genomes from wider geographical regions and diverse hosts are needed to better understand the classification within this genus.