scholarly journals Evaluation of the Infectious Potential of Neoparamoeba perurans Following Freshwater Bathing Treatments

2021 ◽  
Vol 9 (5) ◽  
pp. 967
Author(s):  
Richard S. Taylor ◽  
Joel Slinger ◽  
Chris Stratford ◽  
Megan Rigby ◽  
James W. Wynne
Keyword(s):  
Atlantic Salmon ◽  
Post Treatment ◽  
In Vitro Studies ◽  
Post Inoculation ◽  
Risk Of Infection ◽  
Gill Disease ◽  
Farmed Atlantic Salmon ◽  
Infectious Potential

Freshwater bathing for 2–3 h is the main treatment to control amoebic gill disease of marine-farmed Atlantic salmon. Recent in vitro studies have demonstrated that amoebae (Neoparamoeba perurans) detach when exposed to freshwater and that some eventually reattach to culture plates when returned to seawater. Here, we evaluated the potential for gill-detached N. perurans to survive a commercially relevant treatment and infect AGD-naïve fish and whether holding used bathwater for up to 6 h post treatment would lower infectivity. AGD-affected fish were bathed in freshwater for 2 h. Naïve salmon were exposed to aliquots of the used bathwater after 2, 4, 6 and 8 h. The inoculation was performed at 30 ppt for 2 h, followed by gradual dilution with seawater. Sampling at 20 days post inoculation (dpi) and 40 dpi confirmed rapid AGD development in fish inoculated in 2 h used bathwater, but a slower AGD development following exposure to 4 h bathwater. AGD signs were variable and reduced following longer bathwater holding times. These results suggest that viable amoebae are likely returned to seawater following commercial freshwater treatments, but that the risk of infection can be reduced by retention of bathwater before release.

scholarly journals Cyclic Hypoxia Exposure Accelerates the Progression of Amoebic Gill Disease

Pathogens ◽  
2020 ◽  
Vol 9 (8) ◽  
pp. 597
Author(s):  
Tina Oldham ◽  
Tim Dempster ◽  
Philip Crosbie ◽  
Mark Adams ◽  
Barbara Nowak
Keyword(s):  
Atlantic Salmon ◽  
Economic Losses ◽  
Post Inoculation ◽  
Diel Pattern ◽  
Marine Aquaculture ◽  
Hypoxia Exposure ◽  
Qpcr Analysis ◽  
Serious Infections ◽  
Gill Disease ◽  
Hypoxic Treatment

Amoebic gill disease (AGD), caused by the amoeba Neoparamoeba perurans, has led to considerable economic losses in every major Atlantic salmon producing country, and is increasing in frequency. The most serious infections occur during summer and autumn, when temperatures are high and poor dissolved oxygen (DO) conditions are most common. Here, we tested if exposure to cyclic hypoxia at DO saturations of 40–60% altered the course of infection with N. perurans compared to normoxic controls maintained at ≥90% DO saturation. Although hypoxia exposure did not increase initial susceptibility to N. perurans, it accelerated progression of the disease. By 7 days post-inoculation, amoeba counts estimated from qPCR analysis were 1.7 times higher in the hypoxic treatment than in normoxic controls, and cumulative mortalities were twice as high (16 ± 4% and 8 ± 2%), respectively. At 10 days post-inoculation, however, there were no differences between amoeba counts in the hypoxic and normoxic treatments, nor in the percentage of filaments with AGD lesions (control = 74 ± 2.8%, hypoxic = 69 ± 3.3%), or number of lamellae per lesion (control = 30 ± 0.9%, hypoxic = 27.9 ± 0.9%) as determined by histological examination. Cumulative mortalities at the termination of the experiment were similarly high in both treatments (hypoxic = 60 ± 2%, normoxic = 53 ± 11%). These results reveal that exposure to cyclic hypoxia in a diel pattern, equivalent to what salmon are exposed to in marine aquaculture cages, accelerated the progression of AGD in post-smolts.

Temporal changes in infections with some pathogens associated with gill disease in farmed Atlantic salmon ( Salmo salar L)

Aquaculture ◽  
2017 ◽  
Vol 468 ◽  
pp. 126-134 ◽  
Author(s):  
G.S Gunnarsson ◽  
E Karlsbakk ◽  
S Blindheim ◽  
H Plarre ◽  
A.K Imsland ◽  
...  
Keyword(s):  
Atlantic Salmon ◽  
Salmo Salar ◽  
Temporal Changes ◽  
Atlantic Salmon Salmo Salar ◽  
Gill Disease ◽  
Farmed Atlantic Salmon

scholarly journals Pilchard orthomyxovirus (POMV). II. Causative agent of salmon orthomyxoviral necrosis, a new disease of farmed Atlantic salmon Salmo salar

2020 ◽  
Vol 139 ◽  
pp. 51-68 ◽  
Author(s):  
SE Godwin ◽  
RN Morrison ◽  
G Knowles ◽  
MC Cornish ◽  
D Hayes ◽  
...  
Keyword(s):  
Cell Culture ◽  
Atlantic Salmon ◽  
Infected Fish ◽  
Direct Role ◽  
Multiple Organs ◽  
Direct Exposure ◽  
Salmon Fry ◽  
Infected Cells ◽  
Farmed Atlantic Salmon

Since 2012, an orthomyxo-like virus has been consistently linked to epizootics in marine farmed Atlantic salmon in Tasmania, Australia. Here we describe the properties of the virus, designated the pilchard orthomyxovirus (POMV), in cell culture and present data verifying its direct role in a disease of Atlantic salmon. In infected cells, viral RNA was detectable in both the nucleus and cytoplasm, consistent with the replication cycle of an orthomyxovirus. Viral replication in vitro was temperature-dependent (within a range of 10-20°C), and yields of virus were typically in excess of 107 TCID50 ml-1. In controlled infection trials, cell culture-derived POMV produced significant morbidity in Atlantic salmon fry, pre-smolt and post-smolt. In all cases, the development of disease was rapid, with moribund fish detected within 5 d of direct exposure to POMV, and maximum cumulative morbidity occurring within 4 wk. The experimentally infected fish developed a characteristic suite of gross and microscopic pathological changes, which were consistent with those observed in Atlantic salmon overtly affected by POMV-associated disease on sea farms. These included necrotic lesions across multiple organs that were directly associated with the presence of the virus. Together, our observations indicate that POMV is an endemic virus likely transmitted from wild fish to farmed Atlantic salmon in Tasmania. The virus is pathogenic to Atlantic salmon in freshwater and marine environments and causes a disease that we have named salmon orthomyxoviral necrosis.

scholarly journals Dynamic Gill and Mucous Microbiomes Track an Amoebic Gill Disease Episode in Farmed Atlantic Salmon

2020 ◽  
Author(s):  
Victor Blasco Birlanga ◽  
Grace McCormack ◽  
Umer Zeeshan Ijaz ◽  
Eugene McCarthy ◽  
Cindy Smith ◽  
...  
Keyword(s):  
Atlantic Salmon ◽  
Rrna Genes ◽  
Prokaryotic Community ◽  
Sampling Campaign ◽  
Healthy State ◽  
Disease Episode ◽  
Gill Disease ◽  
Farmed Atlantic Salmon ◽  
18S Rrna Genes ◽  
Pcr Targeting

Abstract Background Amongst gill disorders in Atlantic salmon, amoebic gill disease (AGD) is currently one of the most common and virulent, resulting in large losses for the aquaculture industry. However, our understanding of the role of the gill microbiome during AGD development is limited. Thus, we undertook a longitudinal study with the main objective of characterising the microbiome of gill, and mucous, samples from farmed Atlantic salmon before, and during, an AGD episode. Using a newly optimised DNA extraction protocol, we sequenced rRNA genes from 90 Atlantic salmon gill microbiomes from a fish farm (West coast of Ireland) over the course of a summer season. The first aetiological agent of AGD, Neoparamoeba perurans , was quantified using PCR targeting 18S rRNA genes. The same analyses were done using mucous samples as suitable, non-lethal alternatives to gill samples. Microbiome features across the sampling campaign were distinguished, focusing on patterns before and during the AGD episode. Results The richness and balance of the prokaryotic community on gills were trending upwards prior to the first appearance of AGD symptoms. The microbiome changed significantly, with reduced diversity and balance, after the AGD episode was confirmed, and the changing bacterial community was driven by competitive exclusion. However, this trend was reversed with the application of a first, and a second, freshwater bath treatment. Mucous samples behaved similarly. The variance of the entire prokaryotic community from both gill and mucous samples was significantly affected by the abundance of N. perurans . Rubritalea sp. were abundant in every gill and mucous sample; however, other genera ( Dyadobacter, Shewanella and Pedobacter ) were maximally abundant in gill and mucous samples 12 days prior to the first detection of AGD symptoms. Conclusions Gill and mucous microbiomes changed significantly after the first AGD symptoms were evident, correlating with N. perurans concentrations and supporting a connection between the development of the AGD and the gill microbiome. Those changes, however, were reversed by the application of multiple freshwater treatments, which returned gills to a more healthy state. Despite differences between microbiome features from gill and mucous samples, the data establish mucous scrapings as suitable, non-lethal substitutes for partial characterisation of the whole prokaryotic community from fish gills. The genus Shewanella was widely present, and significantly more abundant, immediately before the first AGD symptoms than during the AGD episode, marking this out as a feasible, putative target in identifying proxies for early detection of AGD.

Local and systemic humoral immune response in farmed Atlantic salmon ( Salmo salar L.) under a natural amoebic gill disease outbreak

2017 ◽  
Vol 66 ◽  
pp. 207-216 ◽  
Author(s):  
Mar Marcos-López ◽  
Cristóbal Espinosa Ruiz ◽  
Hamish D. Rodger ◽  
Ian O'Connor ◽  
Eugene MacCarthy ◽  
...  
Keyword(s):  
Immune Response ◽  
Atlantic Salmon ◽  
Salmo Salar ◽  
Humoral Immune Response ◽  
Disease Outbreak ◽  
Humoral Immune ◽  
Atlantic Salmon Salmo Salar ◽  
Gill Disease ◽  
Farmed Atlantic Salmon

scholarly journals A diversity of amoebae colonise the gills of farmed Atlantic salmon (Salmo salar) with amoebic gill disease (AGD)

2019 ◽  
Vol 67 ◽  
pp. 27-45 ◽  
Author(s):  
Chloe J. English ◽  
Tomáš Tyml ◽  
Natasha A. Botwright ◽  
Andrew C. Barnes ◽  
James W. Wynne ◽  
...  
Keyword(s):  
Atlantic Salmon ◽  
Salmo Salar ◽  
Atlantic Salmon Salmo Salar ◽  
Gill Disease ◽  
Farmed Atlantic Salmon
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