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Barbara F. Nowak - One of the best experts on this subject based on the ideXlab platform.
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Experimental Challenge Models and In Vitro Models to Investigate Efficacy of Treatments and Vaccines against Amoebic Gill Disease.
Microorganisms, 2021Co-Authors: Jemma Hudson, Barbara F. NowakAbstract:Amoebic Gill Disease (AGD) severely affects salmonid mariculture due to fish losses and costs associated with management of the Disease. Continued research into management solutions, including new treatments and vaccine development, is highly important for the future of salmonid production worldwide. This requires both in vitro (both pathogen only and host-pathogen models) and in vivo (Disease challenge) testing. Challenge models are still widely varied, in particular with regard to: infection methods (cohabitation or immersion), source of the pathogen (isolated from infected fish or cultured), infectious dose, environmental conditions (in particular temperature) and the endpoints across experimental treatment and vaccine studies which makes comparisons between studies difficult. This review summarises in vitro assays, the challenge methods and endpoints used in studies of experimental treatments and vaccines for AGD.
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Experimental exposure to low concentrations of Neoparamoeba perurans induces Amoebic Gill Disease in Atlantic salmon.
Journal of fish diseases, 2021Co-Authors: Andrew R. Bridle, Philip Crosbie, Thomas Hill, Aaron Smith, Barbara F. NowakAbstract:Amoebic Gill Disease (AGD) is a significant issue in Atlantic salmon mariculture. Research on the development of treatments or vaccines uses experimental challenges where salmon is exposed to amoebae concentrations ranging from 500 to 5,000/L. However, the water concentrations of N. perurans on affected salmon farms are much lower. The lowest concentration of N. perurans previously reported to cause AGD was 10/L. Here, we report that concentrations as low as 0.1/L of N. perurans can cause AGD. We propose that concentrations of N. perurans that reflect those measured on salmon farms should be used for future experimental challenges.
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Multilocus Sequence Typing (MLST) and Random Polymorphic DNA (RAPD) Comparisons of Geographic Isolates of Neoparamoeba perurans, the Causative Agent of Amoebic Gill Disease
Pathogens (Basel Switzerland), 2019Co-Authors: Jessica C. Johnson-mackinnon, Egil Karlsbakk, Barbara F. Nowak, Philip B. B. Crosbie, Richard Paley, Mar Marcos-lopez, Andrew R. BridleAbstract:Neoparamoba perurans, is the aetiological agent of Amoebic Gill Disease (AGD), a Disease that affects farmed Atlantic salmon worldwide. Multilocus sequence typing (MLST) and Random Amplified Polymorphic DNA (RAPD) are PCR-based typing methods that allow for the highly reproducible genetic analysis of population structure within microbial species. To the best of our knowledge, this study represents the first use of these typing methods applied to N. perurans with the objective of distinguishing geographical isolates. These analyses were applied to a total of 16 isolates from Australia, Canada, Ireland, Scotland, Norway, and the USA. All the samples from Australia came from farm sites on the island state of Tasmania. Genetic polymorphism among isolates was more evident from the RAPD analysis compared to the MLST that used conserved housekeeping genes. Both techniques consistently identified that isolates of N. perurans from Tasmania, Australia were more similar to each other than to the isolates from other countries. While genetic differences were identified between geographical isolates, a BURST analysis provided no evidence of a founder genotype. This suggests that emerging outbreaks of AGD are not due to rapid translocation of this important salmonid pathogen from the same area.
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Incidence and distribution of Amoebic Gill Disease (AGD) — An epidemiological review
Aquaculture, 2016Co-Authors: Tina Oldham, Hamish D. Rodger, Barbara F. NowakAbstract:Abstract Amoebic Gill Disease (AGD), first documented thirty years ago in sea-caged salmonids, is an ever increasing global concern in finfish aquaculture. The result of Gill infection by Neoparamoeba perurans , clinical AGD has been observed in fourteen countries distributed across six continents and in fifteen species of finfish. The greatest impacts of AGD have been on farmed Atlantic salmon during the seawater grow-out phase. When left untreated AGD has resulted in up to 80% mortality, and even mild infections reduce production performance and fish welfare. This review summarizes and analyses three decades of AGD research and outbreaks, with focus on the causal triad of pathogen, host and environment. Statement of relevance This review provides an improved understanding of AGD including practical applications.
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Amoebic Gill Disease: a growing threat
Microbiology Australia, 2016Co-Authors: Jessica C. Johnson-mackinnon, Tina Oldham, Barbara F. NowakAbstract:The risk of Disease outbreaks is predicted to increase due to climate change. For farmed fish an example is Amoebic Gill Disease (AGD). While initially reported only in farmed salmonids inWashingtonState,USA,andTasmania,Australia, it has nowbecome an issue for Atlantic salmon farmingworldwide and affects a range of other farmedmarinefish species. Local high temperature anomalies and a lack of rainfall have been associatedwith the outbreaks of AGD. Thisworldwide presence is at least partly due to the cosmopolitan natureof theparasite and its lowhost-specificity.TheDisease can be treated using freshwater or hydrogenperoxide baths, but the treatments increase the cost of salmon production. Management of AGD contributes 20% to production costs of Atlantic salmon in Tasmania.
B F Nowak - One of the best experts on this subject based on the ideXlab platform.
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incidence and distribution of Amoebic Gill Disease agd an epidemiological review
Aquaculture, 2016Co-Authors: Tina Oldham, H D Rodger, B F NowakAbstract:Abstract Amoebic Gill Disease (AGD), first documented thirty years ago in sea-caged salmonids, is an ever increasing global concern in finfish aquaculture. The result of Gill infection by Neoparamoeba perurans , clinical AGD has been observed in fourteen countries distributed across six continents and in fifteen species of finfish. The greatest impacts of AGD have been on farmed Atlantic salmon during the seawater grow-out phase. When left untreated AGD has resulted in up to 80% mortality, and even mild infections reduce production performance and fish welfare. This review summarizes and analyses three decades of AGD research and outbreaks, with focus on the causal triad of pathogen, host and environment. Statement of relevance This review provides an improved understanding of AGD including practical applications.
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in vitro cultured neoparamoeba perurans causes Amoebic Gill Disease in atlantic salmon and fulfils koch s postulates
International Journal for Parasitology, 2012Co-Authors: Philip Crosbie, Andrew R. Bridle, K Cadoret, B F NowakAbstract:Abstract Amoebic Gill Disease (AGD) in marine farmed Atlantic salmon is of growing concern worldwide and remains a significant health issue for salmon growers in Australia. Until now the aetiological agent, Neoparamoeba perurans , has not been amenable to in vitro culture and therefore Koch’s postulates could not be fulfilled. The inability to culture the amoeba has been a limiting factor in the progression of research into AGD and required the maintenance of an on-going laboratory-based infection to supply infective material. Culture methods using malt yeast agar with sea water overlaid and subculturing every 3–4 days have resulted in the establishment of a clonal culture of N. perurans , designated clone 4. Identity of the amoeba was confirmed by PCR. After 70 days in culture clone 4 infected Atlantic salmon, causing AGD, and was re-isolated from the infected fish. Diagnosis was confirmed by histology and the infectious agent identified by PCR and in situ hybridisation using oligonucleotide primers and probes previously developed and specific to N. perurans . This study has fulfilled Koch’s postulates for N. perurans as a causative agent of AGD and illustrates its free-living and parasitic nature.
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Amoebic Gill Disease agd in atlantic salmon salmo salar farmed in chile
Aquaculture, 2011Co-Authors: Patricio Bustos, R.n. Morrison, Neil D Young, Marco A Rozas, Harry Bohle, Ricardo S Ildefonso, B F NowakAbstract:Abstract Between May and November 2007, three marine Atlantic salmon farms around Chiloe Island, Chile, reported mortalities in which affected fish presented with Caligus rogercresseyi infections and gross Gill lesions characteristic of Amoebic Gill Disease (AGD). Histological examination of the Gills from affected fish confirmed the presence of AGD lesions. Trophozoites possessing one or more endosymbiotic Perkinsela amoeba -like organisms (PLOs) were observed in association with hyperplastic tissue. Further analyses were undertaken using a combination of PCR and in situ hybridization and the trophozoites were identified as Neoparamoeba perurans . Thus, our data indicate that N. perurans is a causal agent of AGD in Chile. However, it is possible that AGD was not the single cause of mortalities in the epizootics investigated here. The exceptionally high level of co-infection with Caligus rogercresseyi (maximum mean intensity 34, prevalence 100%), could have contributed to the production losses.
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an opportunistic detection of Amoebic Gill Disease in blue warehou seriolella brama gunther collected from an atlantic salmon salmo salar l production cage in south eastern tasmania
Journal of Fish Diseases, 2008Co-Authors: M B Adams, M Villavedra, B F NowakAbstract:Amoebic Gill Disease (AGD) is a recurrent health issue affecting the commercial culture of Atlantic salmon, Salmo salar L., in south eastern Tasmania
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detection of serum anti neoparamoeba spp antibodies in Amoebic Gill Disease affected atlantic salmon salmo salar
Journal of Fish Biology, 2008Co-Authors: Bn Vincent, B F Nowak, R.n. MorrisonAbstract:Amoebic Gill Disease (AGD)-affected Atlantic salmon Salmo salar sometimes developed a serum-antibody response to wild-type Neoparamoeba spp. Five of 103 AGD-affected S. salar sampled possessed detectable antibodies that bound wild-type Neoparamoeba spp. western blotting revealed two distinctly different binding profiles. © 2008 The Authors.
R.n. Morrison - One of the best experts on this subject based on the ideXlab platform.
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Amoebic Gill Disease agd in atlantic salmon salmo salar farmed in chile
Aquaculture, 2011Co-Authors: Patricio Bustos, R.n. Morrison, Neil D Young, Marco A Rozas, Harry Bohle, Ricardo S Ildefonso, B F NowakAbstract:Abstract Between May and November 2007, three marine Atlantic salmon farms around Chiloe Island, Chile, reported mortalities in which affected fish presented with Caligus rogercresseyi infections and gross Gill lesions characteristic of Amoebic Gill Disease (AGD). Histological examination of the Gills from affected fish confirmed the presence of AGD lesions. Trophozoites possessing one or more endosymbiotic Perkinsela amoeba -like organisms (PLOs) were observed in association with hyperplastic tissue. Further analyses were undertaken using a combination of PCR and in situ hybridization and the trophozoites were identified as Neoparamoeba perurans . Thus, our data indicate that N. perurans is a causal agent of AGD in Chile. However, it is possible that AGD was not the single cause of mortalities in the epizootics investigated here. The exceptionally high level of co-infection with Caligus rogercresseyi (maximum mean intensity 34, prevalence 100%), could have contributed to the production losses.
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detection of serum anti neoparamoeba spp antibodies in Amoebic Gill Disease affected atlantic salmon salmo salar
Journal of Fish Biology, 2008Co-Authors: Bn Vincent, B F Nowak, R.n. MorrisonAbstract:Amoebic Gill Disease (AGD)-affected Atlantic salmon Salmo salar sometimes developed a serum-antibody response to wild-type Neoparamoeba spp. Five of 103 AGD-affected S. salar sampled possessed detectable antibodies that bound wild-type Neoparamoeba spp. western blotting revealed two distinctly different binding profiles. © 2008 The Authors.
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Detection of serum anti‐Neoparamoeba spp. antibodies in Amoebic Gill Disease‐affected Atlantic salmon Salmo salar
Journal of Fish Biology, 2008Co-Authors: Bn Vincent, Barbara F. Nowak, R.n. MorrisonAbstract:Amoebic Gill Disease (AGD)-affected Atlantic salmon Salmo salar sometimes developed a serum-antibody response to wild-type Neoparamoeba spp. Five of 103 AGD-affected S. salar sampled possessed detectable antibodies that bound wild-type Neoparamoeba spp. western blotting revealed two distinctly different binding profiles. © 2008 The Authors.
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development of a diagnostic pcr to detect neoparamoeba perurans agent of Amoebic Gill Disease
Journal of Fish Diseases, 2008Co-Authors: Neil D Young, Iva Dyková, B F Nowak, R.n. MorrisonAbstract:Abstract The recent description of Neoparamoeba perurans as an aetiological agent of Amoebic Gill Disease (AGD) advanced our understanding of the condition and has forced a re-evaluation of methods used for the diagnosis of AGD. Currently, there are no tools available that are both specific for N. perurans and suitable for a routine diagnostic procedure. Therefore, in this study we describe an assay to detect N. perurans. The assay, which utilizes PCR to amplify the N. perurans 18S rRNA gene, was shown to be specific and highly sensitive. Neoparamoeba perurans was detected in both Gill samples and primary isolates of non-cultured Gill-derived amoebae obtained during necropsy or biopsy from AGD-affected Atlantic salmon, Salmo salar L. The PCR-based assay provides a simple, flexible tool that will be a useful addition to the diagnostic repertoire for AGD. It may also be used for the genotypic screening of trophozoites during culture and could facilitate further epidemiological and ecological studies of AGD. Keywords: Amoebic Gill Disease, detection, Neoparamoeba perurans, polymerase chain reaction.
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neoparamoeba perurans is a cosmopolitan aetiological agent of Amoebic Gill Disease
Diseases of Aquatic Organisms, 2008Co-Authors: Neil D Young, Iva Dyková, B F Nowak, Kevin Snekvik, R.n. MorrisonAbstract:Previously we described a new member of the Neoparamoeba genus, N. perurans, and showed that it is an agent of Amoebic Gill Disease (AGD) of Atlantic salmon Salmo salar cultured in southeast Tasmania, Australia. Given the broad distribution of cases of AGD, we were interested in extending our studies to epizootics in farmed fish from other sites around the world. Oligonucleotide probes that hybridise with the 18S rRNA of N. perurans, N. branchiphila or N. pemaquidensis were used to examine archival samples of AGD in Tasmania as well as samples obtained from 4 host fish species cultured across 6 countries. In archival samples, N. perurans was the only detectable amoeba, confirming that it has been the predominant aetiological agent of AGD in Tasmania since epizootics were first reported. N. perurans was also the exclusive agent of AGD in 4 host species across 6 countries. Together, these data show that N. perurans is a cosmopolitan agent of AGD and, therefore, of significance to the global mariculture industry.
Mark D. Powell - One of the best experts on this subject based on the ideXlab platform.
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In vitro toxicity of bithionol and bithionol sulphoxide to Neoparamoeba spp., the causative agent of Amoebic Gill Disease (AGD).
Diseases of aquatic organisms, 2010Co-Authors: Renee L Florent, Joy A. Becker, Mark D. PowellAbstract:The objective of the present study was to evaluate the in vitro toxicity of bithionol and bithionol sulphoxide to Neoparamoeba spp., the causative agent of Amoebic Gill Disease (AGD). The current treatment for AGD-affected Atlantic salmon involves bathing sea-caged fish in freshwater for a minimum of 3 h, a labour-intensive and costly exercise. Previous attempts to identify alternative treatments have suggested bithionol as an alternate therapeutic, but extensive in vitro efficacy test- ing has not yet been done. In vitro toxicity to Neoparamoeba spp. was examined using amoebae iso- lated from the Gill of AGD-affected Atlantic salmon and exposing the parasites to freshwater, alumina (10 mg l -1 ), seawater, bithionol or bithionol sulphoxide at nominal concentrations of 0.1, 0.5, 1, 5 and 10 mg l -1 in seawater. The numbers of viable amoebae were counted using the trypan blue exclusion method at 0, 24, 48 and 72 h. Both bithionol and bithionol sulphoxide demonstrated in vitro toxicity to Neoparamoeba spp. at all concentrations examined (0.1 to 10 mg l -1 over 72 h), with a comparable toxicity to freshwater observed for both chemicals at concentrations >5 mg l -1 following a 72 h treat- ment. Freshwater remained the most effective treatment, with only 6% viable amoebae seen after 24 h and no viable amoebae observed after 48 h.
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Increased systemic vascular resistance in Atlantic salmon, Salmo salar L., affected with Amoebic Gill Disease.
Journal of fish diseases, 2007Co-Authors: Mj Leef, James O. Harris, Johnathon Hill, Mark D. PowellAbstract:Previous investigations into the pathophysiology of Amoebic Gill Disease (AGD) have suggested that there are probable cardiovascular effects associated with this Disease. In the present study Atlantic salmon, Salmo salar L., were experimentally infected by cohabitation with Diseased individuals. Two commonly used vasodilators, sodium nitroprusside (SNP) and captopril, the angiotensin-converting enzyme (ACE) inhibitor, were used as tools to investigate possible vasoconstriction and/or renin– angiotensin system (RAS) dysfunction in AGDaffected animals. Within the SNP trial, results showed that AGD-affected fish exhibited lowered cardiac output (Q), lowered cardiac stroke volume (VS) and a significantly elevated systemic vascular resistance (RS) compared with non-affected nai¨ve counterparts. These effects were totally abolished following SNP administration (40 lg kg)1), however significant cardiovascular effects associated with SNP were not observed. Within the captopril trial, where AGD-affected fish were more Diseased compared with the SNP trial, a significant hypertension was observed in AGD-affected fish. Captopril administration (10)4 mol L)1 at 1 mL kg)1) resulted in a significant drop in dorsal aortic pressure (PDA) for both AGD-affected and nai¨ve control fish. In terms of peak individual responses, captopril administration effectively lowered PDA in both AGD-affected and nai¨ve control groups equally. The drop in PDA following SNP administration however was significantly greater in AGD-affected fish potentially suggesting Disease-related vasoconstriction. The lack of significant cardiovascular effects directly associated with both SNP and captopril administrations possibly relate to the 6 h recovery period following surgical procedures. However, while variable, these results do suggest that there are significant cardiovascular effects including vasoconstriction and hypertension associated with AGD.
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Ultrastructural Examination of the Host Cellular Response in the Gills of Atlantic Salmon, Salmo salar, with Amoebic Gill Disease
Veterinary pathology, 2007Co-Authors: Jan Lovy, Joy A. Becker, David J. Speare, Dorota W. Wadowska, Glenda M. Wright, Mark D. PowellAbstract:Gills from Atlantic salmon with experimentally induced Amoebic Gill Disease (Neopar- amoeba spp.) were examined with transmission electron microscopy to assess pathology and host-cell responses. Amoebae were found either on the surface epithelium or with pseudopodia extending deeply into invaginations of epithelial cells. The amoebae had various densities along the plasma membrane and contained electron-dense deposits within their cytoplasm. Surface epithelial cells sloughed from the Gills and had features consistent with apoptosis, including rounded shape, loss of surface microridges, and hypercondensation of nuclear chromatin. Affected areas of Gills had fusion of secondary lamellae with interlamellar spaces occupied by mitotic epithelial cells and eosinophils. Eosinophils contained abundant fusiform-shaped granules that measured approximately 1 mm long and 360 nm wide. The granule consisted of an electron-dense matrix with a central inclusion that was less electron-dense, consisting of particulate and fibrillar material. In many instances, the central inclusion appeared empty and 90% of the eosinophils had morphology suggestive of piecemeal degranulation. Also observed within affected areas were a few neutrophils, mucous cells releasing mucus, and a small number of dendritic-like cells.
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Evaluation of bithionol as a bath treatment for Amoebic Gill Disease caused by Neoparamoeba spp.
Veterinary parasitology, 2006Co-Authors: Renee L Florent, Joy A. Becker, Mark D. PowellAbstract:This study examined the toxicity of bithionol to Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss in fresh- and seawater and the efficacy of bithionol as a 1h seawater bath treatment for Amoebic Gill Disease (AGD). To examine toxicity, fish were bathed for 1, 3 and 6h in bithionol, an anti-protozoal at 0, 1, 5, 10, 25 and 35mgL(-1) with toxicity determined by time to morbidity. Efficacy was examined by bathing AGD-affected Atlantic salmon and rainbow trout for 1h at bithionol concentrations of 1-25mgL(-1). Efficacy was determined by examining Gill amoeba counts and identifying percent lesioned Gill filaments at 1 and 24h after bath exposure to bithionol. For both species, bithionol was determined to be toxic at 25 and 35mgL(-1) exhibiting median lethal times (LT50s) ranging from 21 to 84min. Morbidity occurred in the 5 and 10mgL(-1) treatments, however, due to sampling regime there were not enough fish available to calculate LT50s. Only bithionol at 1mgL(-1) was considered non-toxic with no signs of morbidity. Bithionol was more toxic in seawater than freshwater and had no acute effects on Gill Na+/K+ ATPase and succinic dehydrogenase, or plasma osmolality and chloride concentration. Bithionol at 1mgL(-1) reduced percent lesioned Gill filaments in Atlantic salmon and rainbow trout by 33 and 27 per cent, respectively, compared to the seawater control. Similarly, numbers of amoeba were reduced by 33 and 43 per cent for Atlantic salmon and rainbow trout, respectively, when compared to the seawater control. Furthermore, bithionol reduced percent lesioned Gill filaments as much as did the current industry standard of freshwater. This study demonstrated that a 1h seawater bath containing 1mgL(-1) bithionol could be an improvement to the current method of treatment for AGD-affected Atlantic salmon and rainbow trout.
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Respiratory pathogenesis of Amoebic Gill Disease (AGD) in experimentally infected Atlantic salmon Salmo salar.
Diseases of aquatic organisms, 2005Co-Authors: Mj Leef, James O. Harris, Mark D. PowellAbstract:The aim of this study was to investigate the respiratory responses of Atlantic salmon, Salmo salar, experimentally affected with Amoebic Gill Disease (AGD). In Series I, arterial blood samples were taken over a 96 h period following amoebae addition to examine potential respiratory effects associated with initial exposure. No major significant treatment effects were found between fish exposed to amoebae and control (non-exposed) fish. Arterial pH (pH a) was seen to be significantly elevated at 48 h in AGD fish relative to the 0 h time point. To investigate the long-term respiratory effects associated with infection, fish were similarly exposed to amoebae and sampled over a 16 d period. As for Series I, caudal blood pH was significantly elevated by Day 2 (48 h) compared to the pre (Day 0)-time point, suggesting that initial exposure to amoebae and/or amoebae attachment may have induced an initial respiratory alkalosis via increased ventilation frequency and/or amplitude. From Day 7 onwards, and coinciding with a significant increase in the percentage of affected Gill filaments, blood pH decreased significantly, possibly indicating the onset of the characteristic respiratory acidosis that has previously been described for experimentally AGD-affected Atlantic salmon. Although fish in this study showed up to 90 % AGD-affected filaments, the corresponding respiratory results do not reflect a major acid-base disturbance. Therefore, the findings from the present study support the contention that, although AGD only affects the Gill, AGD-associated mortality in Atlantic salmon may not be primarily associated with respiratory failure. © Inter-Research 2005.
Nicholas G. Elliott - One of the best experts on this subject based on the ideXlab platform.
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Salmonid heterosis for resistance to Amoebic Gill Disease (AGD)
Aquaculture, 2016Co-Authors: Ben T. Maynard, Richard S. Taylor, Peter D. Kube, Mathew T. Cook, Nicholas G. ElliottAbstract:Amoebic Gill Disease (AGD) has been an economically significant problem for the Tasmanian Atlantic salmon Salmo salar aquaculture industry for over 25 years. More recently, AGD has emerged as a major issue in other growing regions. Freshwater bathing remains the most effective treatment, although progress with selective breeding has shown that there are genetic mechanisms for resistance to be exploited. In this study, we compared the AGD resistance of Atlantic salmon, brown trout (Salmo trutta), and their interspecies hybrid. Using 22 Atlantic salmon and 20 brown trout broodstock in a factorial mating design, populations of Atlantic salmon, brown trout, and each reciprocal hybrid were produced. All populations were transferred to sea cages at 15 months of age and subjected to natural, chronic AGD challenge under semi-commercial conditions for six months. Disease severity was monitored over four infection cycles and AGD resistance calculated using Gill scoring, a previously reported, industry-standard measure of gross AGD pathology. While the Atlantic salmon population became infected and required freshwater bathing four times during the trial, both hybrids and brown trout became infected and required bathing only once. Heterosis for AGD resistance was significant, with hybrids displaying up to a 69% improvement over the mid-parent average and a 48% improvement over the best parent. The brown trout ♀ × Atlantic salmon ♂ (TS) population exhibited the highest levels of AGD resistance throughout the study, which covered the rearing of animals up until 21 months of age. Over this period the TS hybrid performed comparably to Atlantic salmon for growth rate and survival. The Atlantic salmon × brown trout hybrid represents a model for further exploitation to advance the understanding of AGD resistance in salmonids, and may provide options for commercial growers.
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Gill observations in Atlantic salmon (Salmo salar, L.) during repeated Amoebic Gill Disease (AGD) field exposure and survival challenge
Aquaculture, 2009Co-Authors: Richard S. Taylor, Peter D. Kube, Mathew T. Cook, Warren J. Müller, Nicholas G. ElliottAbstract:Abstract Amoebic Gill Disease (AGD) of Atlantic salmon in Tasmania is proactively treated by freshwater bathing when gross Gill assessment (‘Gill score’) indicates a moderate level of Disease in a cage population. This generally ensures that few fish are exposed to severe Disease symptoms and that few die, but also means that a proportion of the population shows little gross evidence of AGD. Individuals exhibiting few AGD symptoms at bath may be more resistant, or simply reflect an uneven spread of the Disease through the population. This study had three main aims, firstly, to determine whether all fish in a cage population eventually require freshwater treatment after first infection; secondly, to ascertain whether there is any evidence of development of resistance to AGD; and thirdly, to see if there is a relationship between the level of proliferative Gill reaction to the parasite, assessed by Gill score, and time to mortality when the Disease is left untreated. These aims were achieved by following Gill score trajectories of individual fish through three rounds of natural AGD infection and relating these to the eventual fate of the fish in a natural AGD survival challenge after the second freshwater bath. There was no evidence of complete innate resistance to AGD as each fish eventually required a first freshwater bath. There was no relationship between the rate of first infection and the ultimate survival of each fish. For the second and third exposures, significant differences ( P
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Transcriptome Analyses of Amoebic Gill Disease-affected Atlantic Salmon (Salmo salar) Tissues Reveal Localized Host Gene Suppression
Marine Biotechnology, 2008Co-Authors: James W. Wynne, Barbara F. Nowak, Mathew T. Cook, Glenn Stone, Maree G. O’sullivan, David R. Lovell, Nicholas G. ElliottAbstract:The transcriptome response of Atlantic salmon ( Salmo salar ) displaying advanced stages of Amoebic Gill Disease (AGD) was investigated. Naïve smolt were challenged with AGD for 19 days, at which time all fish were euthanized and their severity of infection quantified through histopathological scoring. Gene expression profiles were compared between heavily infected and naïve individuals using a 17 K Atlantic salmon cDNA microarray with real-time quantitative RT-PCR (qPCR) verification. Expression profiles were examined in the Gill, anterior kidney, and liver. Twenty-seven transcripts were significantly differentially expressed within the Gill; 20 of these transcripts were down-regulated in the AGD-affected individuals compared with naïve individuals. In contrast, only nine transcripts were significantly differentially expressed within the anterior kidney and five within the liver. Again the majority of these transcripts were down-regulated within the Diseased individuals. A down-regulation of transcripts involved in apoptosis (procathepsin L, cathepsin H precursor, and cystatin B) was observed in AGD-affected Atlantic salmon. Four transcripts encoding genes with antioxidant properties also were down-regulated in AGD-affected Gill tissue according to qPCR analysis. The most up-regulated transcript within the Gill was an unknown expressed sequence tag (EST) whose expression was 218-fold (± SE 66) higher within the AGD affected Gill tissue. Our results suggest that Atlantic salmon experiencing advanced stages of AGD demonstrate general down-regulation of gene expression, which is most pronounced within the Gill. We propose that this general gene suppression is parasite-mediated, thus allowing the parasite to withstand or ameliorate the host response.
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Resistance to Amoebic Gill Disease (AGD) is characterised by the transcriptional dysregulation of immune and cell cycle pathways
Science & Engineering Faculty, 2008Co-Authors: James W. Wynne, Barbara F. Nowak, Richard S. Taylor, Mathew T. Cook, Maree O'sullivan, Glenn Stone, David Lovell, Nicholas G. ElliottAbstract:Amoebic Gill Disease (AGD) is a parasite-mediated proliferative Gill Disease capable of affecting a range of teleost hosts. While a moderate heritability for AGD resistance in Atlantic salmon has been reported previously, the mechanisms by which individuals resist the proliferative effects remain poorly understood. To gain more knowledge of this commercially important trait, we compared Gill transcriptomes of two groups of Atlantic salmon, one designated putatively resistant, and one designated putatively susceptible to AGD. Utilising a 17k Atlantic salmon cDNA microarray we identified 196 transcripts that were differentially expressed between the two groups. Expression of 11 transcripts were further examined with real-time quantitative RT-PCR (qPCR) in the AGD-resistant and AGD-susceptible animals, as well as non-infected naive fish. Gene expression determined by qPCR was in strong agreement with the microarray analysis. A large number of differentially expressed genes were involved in immune and cell cycle responses. Resistant individuals displayed significantly higher expression of genes involved in adaptive immunity and negative regulation of the cell cycle. In contrast, AGD-susceptible individuals showed higher expression of acute phase proteins and positive regulators of the cell cycle. Combined with the Gill histopathology, our results suggest AGD resistance is acquired rather than innately present, and that this resistance is for the most part associated with the dysregulation of immune and cell cycle pathways. © 2008 Elsevier Ltd. All rights reserved.
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transcriptome analyses of Amoebic Gill Disease affected atlantic salmon salmo salar tissues reveal localized host gene suppression
Science & Engineering Faculty, 2008Co-Authors: James W. Wynne, B F Nowak, Mathew T. Cook, Glenn Stone, David Lovell, Maree Osullivan, Nicholas G. ElliottAbstract:The transcriptome response of Atlantic salmon (Salmo salar) displaying advanced stages of Amoebic Gill Disease (AGD) was investigated. Naive smolt were challenged with AGD for 19 days, at which time all fish were euthanized and their severity of infection quantified through histopathological scoring. Gene expression profiles were compared between heavily infected and naive individuals using a 17 K Atlantic salmon cDNA microarray with real-time quantitative RT-PCR (qPCR) verification. Expression profiles were examined in the Gill, anterior kidney, and liver. Twenty-seven transcripts were significantly differentially expressed within the Gill; 20 of these transcripts were down-regulated in the AGD-affected individuals compared with naive individuals. In contrast, only nine transcripts were significantly differentially expressed within the anterior kidney and five within the liver. Again the majority of these transcripts were down-regulated within the Diseased individuals. A down-regulation of transcripts involved in apoptosis (procathepsin L, cathepsin H precursor, and cystatin B) was observed in AGD-affected Atlantic salmon. Four transcripts encoding genes with antioxidant properties also were down-regulated in AGD-affected Gill tissue according to qPCR analysis. The most up-regulated transcript within the Gill was an unknown expressed sequence tag (EST) whose expression was 218-fold (± SE 66) higher within the AGD affected Gill tissue. Our results suggest that Atlantic salmon experiencing advanced stages of AGD demonstrate general down-regulation of gene expression, which is most pronounced within the Gill. We propose that this general gene suppression is parasite-mediated, thus allowing the parasite to withstand or ameliorate the host response. © 2008 Springer Science+Business Media, LLC.