Common dab, Limanda limanda (L.), as a natural carrier of salmonid alphavirus (SAV) from waters off north‐west Ireland

Abstract

Keywords: common dab, pancreas disease, salmonid alphavirus.Pancreas disease (PD) and sleeping disease (SD) are important, largely chronic conditions of farmed Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss), respectively, and are caused by salmonid alphavirus (SAV) (Togaviridae) (McLoughlin & Graham 2007). Six SAV subtypes have been distinguished to date utilizing the partial E2 and nsP3-gene sequence data with subtypes I, IV, V and VI present in Scotland and Ireland, subtype II dominant in the UK and continental Europe and subtype III restricted to Norway (Fringuelli et al. 2008). The first evidence of a wild reservoir for SAV was reported by Snow et al. (2010) where SAV V was detected in several species of flatfish (Pleuronectidae), and later on, Bruno et al. (2014) and McCleary et al. (2014) confirmed the presence of SAV I, II and V in common dab and plaice. Also for first time the virus was successfully cultured on a salmonidderived cell line (Bruno et al. 2014). The present article aims to survey SAV in common dab from waters off the north-west coast of Ireland and report on apparent prevalence in wild fish.In total, 120 common dab were collected in Irish waters approximately 70 nautical miles from the north-west coast in February 2012 (Fig. 1).Gross changes consistent with epidermal hyperplasia/papilloma, lymphocystis and acute/healing skin ulcers and hyperpigmentation on the ocular side from individual dab were noted. Total RNA was extracted from 5 mg of heart tissue (QIAsymphony RNA Kit; Qiagen), genomic DNA was removed (DNA-free TM DNA Removal Kit; Life Technologies), and cDNA was synthesized (Snow et al. 2010). A nsP1 RT-qPCR assay (Hodneland & Endresen 2006) and 12s RNA endogenous control assay (McCleary et al. 2014) were run on the LightCycler â 480 detection system (Roche) using Quanta Custom Toughmix (Quanta Biosciences). A sample was recorded as SAV positive when crossing point (Cp) values were generated in all three replicates. Partial E2 gene was amplified using a nested PCR and sequenced according to Bruno et al. (2014). Virus culturing was attempted using heart and kidney tissue shown positive by nsP1 RT-qPCR. The prevalence and 95% confidence intervals (CI) were estimated from a generalized linear model assuming a binomial error distribution and comprising the intercept only as the explanatory variable (Nelder & Wedderburn 1972).Four dab tested SAV positive by nsP1 RT-qPCR assay in all triplicates (Table 1). This corresponds to an apparent prevalence of SAV type I of 3.3% (95% CI 1.3%-8.5%). No cytopathic effect was observed in the tissue culture, and supernatant tested negative for SAV by RT-qPCR. Sequencing was attempted from all positive samples, and a partial E2 sequence (KP091737) was obtained for one sample (2013/0118/048). This sequence showed 100% identity to the dab SAV type I detected in the Dublin Bay (Ireland) (f10_4, 5 and 6) and Celtic Sea (f12_181) and interestingly was also identical to SAV 4640 isolate from the Scottish farmed Atlantic salmon (SCO 07-887...

Establishment and Characterization of a Novel Gill Cell Line, LG-1, from Atlantic Lumpfish (Cyclopterus lumpus L.)

“…This susceptibility of lumpfish to SAV1 is novel and highly interesting, as the marine reservoirs for the different SAV genotypes have not been identified. Although some SAV genotypes have been found in marine fish species like the common dab [ 43 , 44 ], pancreas disease is only described in salmonids [ 45 ].…”

Isolation of salmonid alphavirus subtype 6 from wild‐caught ballan wrasse, Labrus bergylta (Ascanius)

“…Historically, SAV was only isolated from Atlantic salmon and rainbow trout causing pancreas disease and sleeping disease, respectively. In recent years, SAV has been detected in nonsalmonids, namely wild common dab, Limanda limanda (L.), and European plaice, Pleuronectes platessa (L.), off the coast of Ireland (McCleary, Giltrap, Henshilwood, & Ruane, ; Simons, Bruno, Ho, Murray, & Matejusova, ); and common dab, European plaice and long rough dab, Hippoglossoides platessoides (Fabricius), in Scotland (Snow et al., ). In one case, researchers successfully managed to culture a SAV5 isolate from common dab (Bruno et al., ), demonstrating that species other than salmonids are natural carriers of the virus.…”

Ultrastructural insights into the replication cycle of salmon pancreas disease virus (SPDV) using salmon cardiac primary cultures (SCPCs)

“…Longitudinal studies in Scotland (Graham et al, 2006) and Norway (Jansen et al, 2010) have reported sites without clinical PD with SPDV-positive fish detected at slaughter. Extending beyond salmon, this mechanism may also explain non-lethal SPDV infections in other species such as the common dab (Limanda limanda), which does not present with histopathological lesions (Bruno et al, 2014;Simons et al, 2016;Snow et al, 2010).…”

“…Salmon pancreas disease virus also referred to as salmonid alphavirus (SAV) has been reported for over 3 decades affecting farmed salmonids, specifically Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) Villoing et al, 2000). SPDV has also been detected more recently in a nonsalmonid marine species such as the common dab (Limanda limanda) (Bruno et al, 2014;Simons et al, 2016;Snow et al, 2010), suggesting the common dab may act as a wild reservoir for piscine alphavirus.…”