The presence of Apicomplexan parasites in king scallops (Pecten maximus) in Scottish waters.

The king scallop (Pecten maximus) is a commercially important species found around the United Kingdom coast. The association of an Apicomplexan-like parasite with mass mortality of Icelandic scallop (Chlamys islandica) in Iceland and the presence of identical parasites in king scallop (Pecten maximus) and queen scallop (Aequipecten opercularis) in Scotland raised serious concerns regarding the health of Scottish king scallops. Marine Scotland Science (MSS) conducted a survey in 2016 to assess the prevalence and the intensity of parasite infection in king scallops. King scallops were collected and sampled during the annual scallop dredge surveys in the Shetland Isles and the east and west coast of Scotland. The king scallop adductor muscle was macroscopically examined and tissue imprints taken to grade the intensity of infection. The parasite was present in the majority of the king scallops sampled in all surveyed areas: Shetland Isles 87.1%, east coast 76.0% and west coast of Scotland 64.1%. However, the parasitic infestations were light in intensity with the majority of the king scallops graded as 1 (≤20 zoites per microscopic field). No macroscopic changes in the adductor muscle were observed and histopathology examination revealed minor localized fiber degeneration of adjacent fibers to parasite clusters. The results suggested the parasite to be widespread around the Scottish coast and it appears to be able to live within the king scallop at low intensity of infection without causing significant downgrade of the adductor muscle (in terms of colour or texture) or mortality. The partial genome sequence of the parasite in king scallops from Scottish waters was identical to the one reported by Kristmundsson and Freeman (2018) in the Icelandic scallop in Icelandic waters.

Characterization of ranaviruses isolated from lumpfish Cyclopterus lumpus L. in the North Atlantic area: proposal for a new ranavirus species (European North Atlantic Ranavirus).

The commercial production of lumpfish Cyclopterus lumpus L. is expanding with the increased demand for their use as cleaner fish, to control sea-lice numbers, at marine Atlantic salmon Salmo salar L. aquaculture sites throughout Northern Europe. A new ranavirus has been isolated from lumpfish at multiple locations in the North Atlantic area. First isolated in 2014 in the Faroe Islands, the virus has subsequently been found in lumpfish from Iceland in 2015 and from Scotland and Ireland in 2016. The Icelandic lumpfish ranavirus has been characterized by immunofluorescent antibody test, optimal growth conditions and transmission electron microscopy. Partial sequences of the major capsid protein gene from 12 isolates showed 99.79-100% nt identity between the lumpfish ranaviruses. Complete genome sequencing from three of the isolates and phylogenetic analysis based on the concatenated 26 iridovirus core genes suggest these lumpfish ranavirus isolates form a distinct clade with ranaviruses from cod Gadus morhua L. and turbot Scophthalmus maximus L. isolated in Denmark in 1979 and 1999, respectively. These data suggest that these viruses should be grouped together as a new ranavirus species, European North Atlantic Ranavirus, which encompasses ranaviruses isolated from marine fishes in European North Atlantic waters.

Atlantic salmon kidney (ASK) cells are an effective model to characterise interferon (IFN) and IFN-induced gene expression following salmonid alphavirus infection.

Salmonid alphavirus (SAV), the causative agent of pancreas disease, is a serious pathogen of farmed Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). Given the economic impact of SAV outbreaks, much effort is focussed upon understanding the fish immune response following infection and the exploitation of this knowledge to reduce disease impact. Herein we examine the utility of the long-term Atlantic salmon kidney (ASK) cell line as a tool to study antiviral responses upon infection with SAV. Following infection with SAV subtype 1 (isolate V4640) we examined the kinetics and magnitude of induction of IFNa, IFN-regulatory factor (IRF) genes IRF1, IRF3, and IRF7b, as well as the antiviral effector Mx by RT-qPCR. SAV-1 non-structural protein (nsp1) transcript levels increased continuously over the experimental period, indicating viral replication, but cytopathic effect (CPE) was not observed. All the immune genes studied showed an increase in transcript levels over the 96-h study period following SAV infection, with strongest induction of Mx. Our data confirm that ASK cells are a suitable model to study the virus-associated immune responses of salmonids and may be a useful tool when assaying the effectiveness of potential prophylactic or antiviral treatments.

First isolation of Flavobacterium psychrophilum associated with reports of moribund wild European eel (Anguilla anguilla) in Scotland.

In late April 2015, the River Dee Trust informed Marine Scotland Science, Fish Health Inspectorate (FHI), that there had been observations of dead and moribund European eels on the River Dee. Later in May, the Spey Fishery Board also reported a number of moribund European eels in a rotary screw smolt trap on the River Spey. In total, 10 cases involving moribund eels were investigated in 2015 and one case in 2016. In addition, a health screen was conducted to investigate the potential presence of Flavobacterium psychrophilum in healthy eels and Atlantic salmon from the River Dee in 2015. Externally, the diseased eels demonstrated white patches in different locations of the body. In all cases, F. psychrophilum was detected by bacterial isolation and/or molecular methods. Three isolates were further characterized by whole-genome sequencing (WGS) as belonging to sequence type 15 (ST15). Histological examination of diseased European eels revealed lesions at the level of the integument. The pathogen screen for F. psychrophilum in wild healthy fish tested negative by PCR. Further investigation is required to understand the pathogenicity of this bacterium on the health of eels and the potential impact on the wild salmonid population.

Atlantic salmon (Salmo salar L.) serum vitellogenin neutralises infectivity of infectious pancreatic necrosis virus (IPNV).

Vitellogenin is a phosphoglycoprotein which represents the main precursor of the egg yolk in teleost fish. This reproductive protein was also demonstrated to play an important role in innate immunity by acting as a pattern recognition molecule capable of binding to bacteria, fungi and enhancing macrophage phagocytosis. The presented results demonstrate that, egg homogenate, ovarian fluid and serum of mature female Atlantic salmon have high neutralising ability for infectious pancreatic necrosis virus (IPNV). Vitellogenin from mature female Atlantic salmon serum, purified by immuno-affinity on a column matrix coated with monoclonal anti-Atlantic salmon vitellogenin antibody, was able to neutralise between 9.1 x 10(4) and 3.09 x 10(5) TCID(50) IPNV mg(-1) of protein. To the author's knowledge, this is the first time that the neutralising activity of vitellogenin on a teleost virus has been demonstrated. The results may explain why IPNV is difficult to detect by culture methods in ovarian fluid and egg homogenates from carrier mature females and suggest a possible means of vertical transmission via the egg.

Infectious pancreatic necrosis virus suppresses type I interferon signalling in rainbow trout gonad cell line but not in Atlantic salmon macrophages.

RTG-P1 cells are a rainbow trout fibroblastic cell line permanently transfected with the luciferase gene under the control of the Mx promoter. On exposure to interferon (IFN) or IFN inducing agents, the cells produce luciferase. IPNV did not induce luciferase production up to 24h post-infection but did not suppress constitutive luciferase production. Furthermore, IPNV suppressed luciferase production induced by poly I:C. RT-PCR analysis of IPNV infected cells showed IFN gene transcription from 6h post-infection with increasing expression up to 24h. Housekeeping genes beta-actin and GAPDH were also expressed along with upregulation of IRF1 and slight upregulation of STAT1. When RTG-P1 cells were stimulated with IFN, Mx transcripts, measured by qRT-PCR, peaked at 3-6h and thereafter fell to low levels, but in the presence of IPNV, Mx transcription at this time was significantly suppressed but continued to rise gradually. Luciferase production was lower in infected cells at 12h post-infection but not significantly after 24h. These results indicate that, in non-stimulated RTG-P1 cells, while IPNV induces IFN transcription, activation of Mx expression is suppressed. Furthermore, when stimulated by IFN, the rate of Mx transcription is significantly suppressed by the virus. This would probably give time for the virus to replicate rapidly in the early phases of infection. Contrary to the fibroblastic cell line, IPNV stimulated IFN production by salmon macrophages in vitro at least as strongly as poly I:C, with no suppression of the IFN response to poly I:C, and the virus persisted for up to 9 days without causing CPE.