Temporal profile of shedding and clearance of Piscine orthoreovirus (PRV) during pre-smolt stages of Atlantic salmon
1 Purpose.
Piscine orthoreovirus (PRV) causes heart and skeletal muscle inflammation (HSMI) in Atlantic salmon. PRV can cause high morbidity and mortality up to 20% in farmed Atlantic salmon. The virus is ubiquitous and prevalent in all life stages of Atlantic salmon. However, the disease outbreak commonly occurs 5 to 9 months after seawater transfer. The disease outbreak reported in seawater transfer, regardless of the presence of virus in freshwater stage, indicating presence of virus reservoirs in seawater. The virus has been reported from Atlantic salmon freshwater hatcheries in a longitudinal study, however the virus ecology in freshwater remains unknown. There is a lack of knowledge about the disease development, host response and shedding of PRV in infected fry and parr stages.
The objective of this study is to determine the shedding, clearance, and/or persistence of Piscine orthoreovirus (PRV) during pre-smolt stages. The in vivo challenge experiment will determine the susceptibility, shedding and transmission kinetics of Atlantic salmon fry to PRV infection. This study will help us to understand the disease development and viral kinetics during freshwater stages of Atlantic salmon. This part of the challenge experiment will be carried out for a period of approximately 1 year. The effect of smoltification in persistent PRV1 infection will be additionally investigated to determine if this process can act as a stressor to 'reactivate' the virus in chronically-infected fish.
The main hypothesis of the study is that Piscine orthoreovirus (PRV) can cause persistent infection in the pre-smolt stage of Atlantic salmon. The research will attempt to answer other research questions, can the PRV infected fry resolve heart inflammation, are there any differences in antiviral immune response of PRV infected Atlantic salmon fry during early and late stage of infection? Is it possible to use the water from PRV infected experimental tank to infect and cause disease in naïve fry? Does the stress exposure cause recurrence, increase in viral load and shedding of virus during later stage of infection?
Changes in the original experimental plan has been made to maximize the use of the experimental fish that are already persistently-infected with PRV1 for >1 yr. Obtaining this material again will be very difficult. Hence, it is to everyone’s best interest if these fish can be used to answer additional important research questions regarding PRV1 persistence such as:
• Are there other unidentified immuno-privileged site/s for persistent PRV1)?
• Is there a possibility for ‘resurgence’ of persistent PRV1 following stress like smoltification?
If so, is the virus infectious during the entire persistent phase? Or does it get ‘reactivated’ following the transformation from pre-smolt to post-smolt?
2 Distress
The challenge is expected to cause distress and morbidity in fish, and mortality in fish at the fry stage. The persistent infection that is expected to develop in survivors, likely causes much less distress than the 'acute' phase immediately after challenge.
Persistently infected (and mock as control) pre-smolts (~150 g) will undergo photoperiod manipulation and gradual salinity increase over the course of 6 weeks in order to induce smoltification. This treatment is considered to cause moderate stress to the fish. Resurgence of PRV1 infection (from persistent to active infection) may occur in the PRV-1 infected group and thus, will be considered potentially severe for a maximum of 64 post-smolt salmon.
3 Expected benefit.
Improved understanding of infection parameters (e.g. tolerance, persistence, shedding/infectiousness) that govern the the disease transmission and epidemiology of PRV in Norwegian aquaculture (and wild salmon populations).
Please note that requested changes in the original experimental plan has been made to maximize the use of the experimental fish that are already persistently-infected with PRV1 for >1 yr. Obtaining this material again will be very difficult. Hence, it is to everyone’s best interest if these fish can be used to answer additional important research questions regarding PRV1 persistence such as:
• Are there other unidentified immuno-privileged site/s for persistent PRV1)?
• Is there a possibility for ‘resurgence’ of persistent PRV1 following stress like smoltification? If so, is the virus infectious during the entire persistent phase? Or does it get ‘reactivated’ following the transformation from pre-smolt to post-smolt?
4 Number of animals, and what kind
6480 Atlantic salmon (Salmo salar)
5 How to adhere to 3R
Disease in animals happens at the organismal (systemic) level and cannot reliably be 'simulated' by use of e.g. cell models. Appliance with 3R is hence restricted to perform the experiment in the most humane way possible (using strict humane end points etc.) and to ensure an experimental design that maximizes the likelihood of producing important and statistical significant scientific results.
Piscine orthoreovirus (PRV) causes heart and skeletal muscle inflammation (HSMI) in Atlantic salmon. PRV can cause high morbidity and mortality up to 20% in farmed Atlantic salmon. The virus is ubiquitous and prevalent in all life stages of Atlantic salmon. However, the disease outbreak commonly occurs 5 to 9 months after seawater transfer. The disease outbreak reported in seawater transfer, regardless of the presence of virus in freshwater stage, indicating presence of virus reservoirs in seawater. The virus has been reported from Atlantic salmon freshwater hatcheries in a longitudinal study, however the virus ecology in freshwater remains unknown. There is a lack of knowledge about the disease development, host response and shedding of PRV in infected fry and parr stages.
The objective of this study is to determine the shedding, clearance, and/or persistence of Piscine orthoreovirus (PRV) during pre-smolt stages. The in vivo challenge experiment will determine the susceptibility, shedding and transmission kinetics of Atlantic salmon fry to PRV infection. This study will help us to understand the disease development and viral kinetics during freshwater stages of Atlantic salmon. This part of the challenge experiment will be carried out for a period of approximately 1 year. The effect of smoltification in persistent PRV1 infection will be additionally investigated to determine if this process can act as a stressor to 'reactivate' the virus in chronically-infected fish.
The main hypothesis of the study is that Piscine orthoreovirus (PRV) can cause persistent infection in the pre-smolt stage of Atlantic salmon. The research will attempt to answer other research questions, can the PRV infected fry resolve heart inflammation, are there any differences in antiviral immune response of PRV infected Atlantic salmon fry during early and late stage of infection? Is it possible to use the water from PRV infected experimental tank to infect and cause disease in naïve fry? Does the stress exposure cause recurrence, increase in viral load and shedding of virus during later stage of infection?
Changes in the original experimental plan has been made to maximize the use of the experimental fish that are already persistently-infected with PRV1 for >1 yr. Obtaining this material again will be very difficult. Hence, it is to everyone’s best interest if these fish can be used to answer additional important research questions regarding PRV1 persistence such as:
• Are there other unidentified immuno-privileged site/s for persistent PRV1)?
• Is there a possibility for ‘resurgence’ of persistent PRV1 following stress like smoltification?
If so, is the virus infectious during the entire persistent phase? Or does it get ‘reactivated’ following the transformation from pre-smolt to post-smolt?
2 Distress
The challenge is expected to cause distress and morbidity in fish, and mortality in fish at the fry stage. The persistent infection that is expected to develop in survivors, likely causes much less distress than the 'acute' phase immediately after challenge.
Persistently infected (and mock as control) pre-smolts (~150 g) will undergo photoperiod manipulation and gradual salinity increase over the course of 6 weeks in order to induce smoltification. This treatment is considered to cause moderate stress to the fish. Resurgence of PRV1 infection (from persistent to active infection) may occur in the PRV-1 infected group and thus, will be considered potentially severe for a maximum of 64 post-smolt salmon.
3 Expected benefit.
Improved understanding of infection parameters (e.g. tolerance, persistence, shedding/infectiousness) that govern the the disease transmission and epidemiology of PRV in Norwegian aquaculture (and wild salmon populations).
Please note that requested changes in the original experimental plan has been made to maximize the use of the experimental fish that are already persistently-infected with PRV1 for >1 yr. Obtaining this material again will be very difficult. Hence, it is to everyone’s best interest if these fish can be used to answer additional important research questions regarding PRV1 persistence such as:
• Are there other unidentified immuno-privileged site/s for persistent PRV1)?
• Is there a possibility for ‘resurgence’ of persistent PRV1 following stress like smoltification? If so, is the virus infectious during the entire persistent phase? Or does it get ‘reactivated’ following the transformation from pre-smolt to post-smolt?
4 Number of animals, and what kind
6480 Atlantic salmon (Salmo salar)
5 How to adhere to 3R
Disease in animals happens at the organismal (systemic) level and cannot reliably be 'simulated' by use of e.g. cell models. Appliance with 3R is hence restricted to perform the experiment in the most humane way possible (using strict humane end points etc.) and to ensure an experimental design that maximizes the likelihood of producing important and statistical significant scientific results.