Amoebic gill disease (AGD) is considered to be the most significant health problem for farmed Atlantic salmon in Tasmania, costing the industry an estimated $15-20 million pa. It is caused by the presence of Neoparamoeba spp. on the gills and if untreated can lead to death. Although some control of the disease is achieved by freshwater bathing, this procedure is not considered a viable, long-term solution. It is not fully efficacious – more than one treatment is usually required; it is very labour-intensive; it requires large volumes of freshwater, and is stressful to the fish, which further impacts on their health and growth. Furthermore, recent experience indicates an increase in the required frequency for freshwater bathing in an attempt to control the disease.

Vaccine development is part of a multifaceted approach to develop short-, medium- and long-term solutions to the control of AGD; development of a sub-unit vaccine being the long-term approach of the overall research strategy. The essential objective is to develop a set of strategies and tools to provide the salmon industry with a substantial reduction to the economic impact of AGD in an economically and environmentally sustainable way.

The most significant outcome of this project is the commencement in July 2007 of sea trials for the experimental DNA vaccine made up of six antigens shown to provide a relative increase in protection of approximately 40 percent in laboratory based amoebic gill disease (AGD) trials.

Keywords: Atlantic salmon, Neoparamoeba, DNA vaccine, recombinant protein, response

Amoebic gill disease (AGD) is considered to be the most significant health problem for farmed Atlantic salmon in Tasmania, costing the industry an estimated $15-20 million pa. It is caused by the presence of Neoparamoeba spp. on the gills and if untreated can lead to death. Although some control of the disease is achieved by freshwater bathing, this procedure is not considered a viable, long-term solution. It is not fully efficacious – more than one treatment is usually required; it is very labour-intensive; it requires large volumes of freshwater, and is stressful to the fish, which further impacts on their health and growth. Furthermore, recent experience indicates an increase in the required frequency for freshwater bathing in an attempt to control the disease.

Vaccine development is part of a multifaceted approach to develop short-, medium- and long-term solutions to the control of AGD; development of a sub-unit vaccine being the long-term approach of the overall research strategy. The essential objective is to develop a set of strategies and tools to provide the salmon industry with a substantial reduction to the economic impact of AGD in an economically and environmentally sustainable way.

The most significant outcome of this project is the commencement in July 2007 of sea trials for the experimental DNA vaccine made up of six antigens shown to provide a relative increase in protection of approximately 40 percent in laboratory based amoebic gill disease (AGD) trials.

Keywords: Atlantic salmon, Neoparamoeba, DNA vaccine, recombinant protein, response

Amoebic gill disease (AGD) is considered to be the most significant health problem for farmed Atlantic salmon in Tasmania, costing the industry an estimated $15-20 million pa. It is caused by the presence of Neoparamoeba spp. on the gills and if untreated can lead to death. Although some control of the disease is achieved by freshwater bathing, this procedure is not considered a viable, long-term solution. It is not fully efficacious – more than one treatment is usually required; it is very labour-intensive; it requires large volumes of freshwater, and is stressful to the fish, which further impacts on their health and growth. Furthermore, recent experience indicates an increase in the required frequency for freshwater bathing in an attempt to control the disease.

Vaccine development is part of a multifaceted approach to develop short-, medium- and long-term solutions to the control of AGD; development of a sub-unit vaccine being the long-term approach of the overall research strategy. The essential objective is to develop a set of strategies and tools to provide the salmon industry with a substantial reduction to the economic impact of AGD in an economically and environmentally sustainable way.

The most significant outcome of this project is the commencement in July 2007 of sea trials for the experimental DNA vaccine made up of six antigens shown to provide a relative increase in protection of approximately 40 percent in laboratory based amoebic gill disease (AGD) trials.

Keywords: Atlantic salmon, Neoparamoeba, DNA vaccine, recombinant protein, response

Before this project our knowledge of immune response in Amoebic Gill Disease (AGD) was fundamentally limited and more  information was required to assess the potential for immunomodulators in the management of AGD.

We confirmed that injection of bacterial DNA motif (CpG oligonucleotides) six days before AGD challenge can offer signficant protection to Atlantic salmon (relative percent survival up to 52.5%).  However, there was no effect if the fish were challenged immediately post injection with bacterial DNA.  This suggests that while there is a potential benefit from the use of immunostimulants, their application is limited because their efficacy is directly linked to the timing of an outbreak, which can be unpredictable in the field. While fish which survived an initial AGD episode show increased resistance to subsequent AGD infection, in contrast to some diseases this effect cannot be simply explained by the presence of antibodies.   The duration of exposure (or number of exposures) appears to be important for the development of serum antibodies.  Mucus antibodies could not be detected in Atlantic salmon that survived AGD challenge.  Microarray experiments and further gene expression studies suggested that there is a loss of cell-cycle control in AGD lesions.  Furthermore, immune pathways are affected since the down-stream effect(s) of the initial inflammatory signals were not detectable.  It is possible that this significantly contributes to the extremely high rate of mortality in unmitigated AGD epizootics.

While we have achieved our objectives and answered many of the original questions, new issues have emerged from our research.  These include a lack of understanding of the mechanisms of inhibition of inflammatory and immune pathways, significance of antibody response (if any) in AGD, and the potential for vaccine antigen discovery through the use of anti-peptide antibody.  The presence and role of a more localised antibody response in the gill mucus or epithelium (currently undetectable) warrants further investigation.  

In conclusion, we now have a better understanding of AGD pathogenesis and the reasons why the host immune response is ineffective in this disease.  In particular, we have shown that immune pathways are inhibited in Atlantic salmon affected by AGD. 

Keywords: Amoebic Gill Disease, salmon, aquaculture, immunostimulants, inflamation, gene expression, transcriptome analysis.

Before this project our knowledge of immune response in Amoebic Gill Disease (AGD) was fundamentally limited and more  information was required to assess the potential for immunomodulators in the management of AGD.

We confirmed that injection of bacterial DNA motif (CpG oligonucleotides) six days before AGD challenge can offer signficant protection to Atlantic salmon (relative percent survival up to 52.5%).  However, there was no effect if the fish were challenged immediately post injection with bacterial DNA.  This suggests that while there is a potential benefit from the use of immunostimulants, their application is limited because their efficacy is directly linked to the timing of an outbreak, which can be unpredictable in the field. While fish which survived an initial AGD episode show increased resistance to subsequent AGD infection, in contrast to some diseases this effect cannot be simply explained by the presence of antibodies.   The duration of exposure (or number of exposures) appears to be important for the development of serum antibodies.  Mucus antibodies could not be detected in Atlantic salmon that survived AGD challenge.  Microarray experiments and further gene expression studies suggested that there is a loss of cell-cycle control in AGD lesions.  Furthermore, immune pathways are affected since the down-stream effect(s) of the initial inflammatory signals were not detectable.  It is possible that this significantly contributes to the extremely high rate of mortality in unmitigated AGD epizootics.

While we have achieved our objectives and answered many of the original questions, new issues have emerged from our research.  These include a lack of understanding of the mechanisms of inhibition of inflammatory and immune pathways, significance of antibody response (if any) in AGD, and the potential for vaccine antigen discovery through the use of anti-peptide antibody.  The presence and role of a more localised antibody response in the gill mucus or epithelium (currently undetectable) warrants further investigation.  

In conclusion, we now have a better understanding of AGD pathogenesis and the reasons why the host immune response is ineffective in this disease.  In particular, we have shown that immune pathways are inhibited in Atlantic salmon affected by AGD. 

Keywords: Amoebic Gill Disease, salmon, aquaculture, immunostimulants, inflamation, gene expression, transcriptome analysis.

Before this project our knowledge of immune response in Amoebic Gill Disease (AGD) was fundamentally limited and more  information was required to assess the potential for immunomodulators in the management of AGD.

We confirmed that injection of bacterial DNA motif (CpG oligonucleotides) six days before AGD challenge can offer signficant protection to Atlantic salmon (relative percent survival up to 52.5%).  However, there was no effect if the fish were challenged immediately post injection with bacterial DNA.  This suggests that while there is a potential benefit from the use of immunostimulants, their application is limited because their efficacy is directly linked to the timing of an outbreak, which can be unpredictable in the field. While fish which survived an initial AGD episode show increased resistance to subsequent AGD infection, in contrast to some diseases this effect cannot be simply explained by the presence of antibodies.   The duration of exposure (or number of exposures) appears to be important for the development of serum antibodies.  Mucus antibodies could not be detected in Atlantic salmon that survived AGD challenge.  Microarray experiments and further gene expression studies suggested that there is a loss of cell-cycle control in AGD lesions.  Furthermore, immune pathways are affected since the down-stream effect(s) of the initial inflammatory signals were not detectable.  It is possible that this significantly contributes to the extremely high rate of mortality in unmitigated AGD epizootics.

While we have achieved our objectives and answered many of the original questions, new issues have emerged from our research.  These include a lack of understanding of the mechanisms of inhibition of inflammatory and immune pathways, significance of antibody response (if any) in AGD, and the potential for vaccine antigen discovery through the use of anti-peptide antibody.  The presence and role of a more localised antibody response in the gill mucus or epithelium (currently undetectable) warrants further investigation.  

In conclusion, we now have a better understanding of AGD pathogenesis and the reasons why the host immune response is ineffective in this disease.  In particular, we have shown that immune pathways are inhibited in Atlantic salmon affected by AGD. 

Keywords: Amoebic Gill Disease, salmon, aquaculture, immunostimulants, inflamation, gene expression, transcriptome analysis.

Prior to this project there had been investigations into some potential candidate amoebicides, with little success except for the possibility of oxidative disinfectants such as chloramine-T.  This project has since tested a number of amoebicides using a progressive approach of in vitro toxicity, in vivo efficacy in the laboratory through to in vivo efficacy under field conditions in either semi-commercial or under full commercialised field trials. 

Although the practical delivery of some of these as treatments of amoebic gill disease (AGD), such as chloramine-T bathing, appear not to be practicable, other avenues may have potential for further commercial development, such as the dietary inclusion of potential amoebicidal compounds, including bithionol and ionophore-based amoebicides.  The project has explored the potential of bithionol, a registered amoebicidal drug, as an in-feed treatment, showing that AGD severity can be reduced by approximately 50%.  Similarly, the project has examined the efficacy of an immunostimulant-based feed additive, Aquacite and Betabec which reduced mortality in Atlantic salmon with AGD but did not affect the intensity of infection.

This project has further characterised the effects of gill disease, in particular AGD, with respect to the metabolic cost of disease to the fish.  This work has estimated that in excess of 17%  of the ingested energy is likely to go to service the cost of AGD.  This approach provides a useful tool to incorporate into bioeconomic models for assessing the efficacy of AGD treatments in the future.

Keywords:  Amoebic gill disease, Atlantic salmon, disease treatment.

Prior to this project there had been investigations into some potential candidate amoebicides, with little success except for the possibility of oxidative disinfectants such as chloramine-T.  This project has since tested a number of amoebicides using a progressive approach of in vitro toxicity, in vivo efficacy in the laboratory through to in vivo efficacy under field conditions in either semi-commercial or under full commercialised field trials. 

Although the practical delivery of some of these as treatments of amoebic gill disease (AGD), such as chloramine-T bathing, appear not to be practicable, other avenues may have potential for further commercial development, such as the dietary inclusion of potential amoebicidal compounds, including bithionol and ionophore-based amoebicides.  The project has explored the potential of bithionol, a registered amoebicidal drug, as an in-feed treatment, showing that AGD severity can be reduced by approximately 50%.  Similarly, the project has examined the efficacy of an immunostimulant-based feed additive, Aquacite and Betabec which reduced mortality in Atlantic salmon with AGD but did not affect the intensity of infection.

This project has further characterised the effects of gill disease, in particular AGD, with respect to the metabolic cost of disease to the fish.  This work has estimated that in excess of 17%  of the ingested energy is likely to go to service the cost of AGD.  This approach provides a useful tool to incorporate into bioeconomic models for assessing the efficacy of AGD treatments in the future.

Keywords:  Amoebic gill disease, Atlantic salmon, disease treatment.

Prior to this project there had been investigations into some potential candidate amoebicides, with little success except for the possibility of oxidative disinfectants such as chloramine-T.  This project has since tested a number of amoebicides using a progressive approach of in vitro toxicity, in vivo efficacy in the laboratory through to in vivo efficacy under field conditions in either semi-commercial or under full commercialised field trials. 

Although the practical delivery of some of these as treatments of amoebic gill disease (AGD), such as chloramine-T bathing, appear not to be practicable, other avenues may have potential for further commercial development, such as the dietary inclusion of potential amoebicidal compounds, including bithionol and ionophore-based amoebicides.  The project has explored the potential of bithionol, a registered amoebicidal drug, as an in-feed treatment, showing that AGD severity can be reduced by approximately 50%.  Similarly, the project has examined the efficacy of an immunostimulant-based feed additive, Aquacite and Betabec which reduced mortality in Atlantic salmon with AGD but did not affect the intensity of infection.

This project has further characterised the effects of gill disease, in particular AGD, with respect to the metabolic cost of disease to the fish.  This work has estimated that in excess of 17%  of the ingested energy is likely to go to service the cost of AGD.  This approach provides a useful tool to incorporate into bioeconomic models for assessing the efficacy of AGD treatments in the future.

Keywords:  Amoebic gill disease, Atlantic salmon, disease treatment.