Royal Society of Edinburgh to investigate ISA

Royal Society of Edinburgh to investigate ISA

An independent working party has been created by The Royal Society of Edinburgh (RSE) to assess the science behind legislation governing the control of Infectious Salmon Anaemia (ISA). A viral disease of salmon, but one which poses no threat to human health, the first outbreak of ISA was detected in 1998 in a salmon farm in Loch Nevis. To date it is known to have spread to 11 farms and has been suspected on a further 25 farms on the Scottish West Coast; in Skye, Orkney, Shetland and the Western Isles. Infection by the virus does not always lead to severe clinical signs of the disease and the death of the fish, yet current European legislation requires that once a fish farm has been designated as infected, all fish will eventually have to be withdrawn, the site disinfected and left fallow for 6 months. There is presently no compensation for any income lost by farmers as a result of this process.

Concerns have been raised about the methods used to identify and verify the presence of the virus in a farm. Fish which have the virus do not necessarily show clinical signs at low levels of infection. Doubts have also been expressed about the accuracy of the viral test methods and the risk of false positive results.

Sir Roderick MacSween, Chairman of the Working party said:

We wish to examine the evidence for ISA being an exotic and not an endemic infection in salmon in Scotland. In addition the scientific basis for establishing viral infection and confirming the presence of virus-related disease must be shown to be robust: implementation of the withdrawal proposal when viral infection is suspected has serious consequences for farmers and, even more significantly, for those breeding salmon stock.

Sir William Stewart, President of The Royal Society of Edinburgh said:

Scotland’s Salmon farming industry is hugely important to our economy. As a nation, we must protect and conserve our environment and our natural resources. This is a complex issue for the environmentalist, for business and for local communities. The RSE has been asked to address this issue and Council has agreed to do so. Our in-depth inquiry must be focused on the science underpinning this issue and advice must be wholly independent and scientifically robust. I am most grateful to Sir Roderick MacSween for agreeing to chair this group. He is a distinguished and experienced chairman and I am confident that he and his team will provide a thorough and detailed analysis of the issue.

The remit of the RSE’s working party is to investigate:

  • The scientific issues surrounding the scheme submitted by the United Kingdom for the withdrawal of all fish in Scottish farms infected with infectious salmon anaemia (ISA), required under EU Directive 2000/27/EC(2)
  • The reliability of detection methods
  • The effectiveness of culling as a means of control, making use of comparisons with regimes for control in other countries
  • The prevalence/incidence and nature of ISA virus in wild and farmed salmon.

The working party is being set up following representations made to the RSE by members of the industry, expressing the view that the current EC legislation is not based on science. The independent group aims to report on its findings to the Council of the RSE by February 2002 and to publish its conclusions widely.

The membership of the Working Party is:

Chair - Sir Roderick MacSween FRSE: Emeritus Professor of Pathology, University of Glasgow

- Professor Ian Aitken: Scientific Director, Edinburgh Centre for Rural Research

Professor Peter Maitland FRSE: Independent Research Consultant, Fish Conservation Centre

Professor Imants Priede FRSE: Professor of Zoology, University of Aberdeen

Professor Stuart Reid FRSE: Professor of Comparative Epidemiology and Informatics, University of Glasgow Veterinary School

Professor John Sargent FRSE: Professor of Marine Biochemistry, Institute of Acquaculture, University of Stirling

Sir William Stewart
: FRS FRSE: President of the RSE

Secretary - Dr Marc Rands: Research Officer, Royal Society of Edinburgh

Background Information on ISA

1.     Infectious Salmon Anaemia (ISA) is a viral disease that affects Atlantic salmon (Salmo salar) but poses no threat to human health.
ISA in Scotland

2.     ISA had been identified in Norway (1984) and Canada (1997) but was thought to be exotic to the European Union before 1998, when it was discovered in a salmon farm in Loch Nevis. To date it has spread to a total of 11 farms and has been suspected on a further 25 farms on the Scottish west coast, Skye, Orkney, Shetland and the Western Isles. All 11 confirmed sites and almost all the 25 sites which were suspect are now back in production after fallowing.
European Legislation concerning ISA and the outbreak in Scotland

3.     In 1991 ISA was classified as a List 1 disease (Council Directive 91/67/EEC (as amended)), which is required to be eradicated under European legislation through control measures initially prescribed in Council Directive 93/53/EEC (see Appendix 1). These control measures required the immediate withdrawal of fish from an infected farm, where official confirmation of infection by laboratory examination or clinical and post-mortem examination had taken place.

4.     Following the outbreak in Scotland in 1998, the European Commission developed proposals for a more pragmatic way to control ISA to allow efficient control of the disease whilst safeguarding as much as possible the interests of the infected sites. These amendments to Council Directive 93/53/EEC, in addition to introducing the possibility for vaccination against the disease, spread the obligation to empty affected fish farms over a period of time (rather than immediately), subject to a withdrawal scheme which required approval by the European Commission. This was to take into account the particular circumstances on the affected site, including fish welfare considerations. For example, a remote farm with low mortalities or few clinical signs in the fish might be allowed a cage by cage clearance programme based on mortality triggers. On the other hand, an infected farm close to other uninfected farms and suffering high mortalities would be required to clear as soon as possible.

5.     In May 2000 the European Commission carried out a Mission to Scotland to assess the situation following the ISA outbreaks. Their report in August 2000, recommended to the Scottish authorities that they should reconsider the decision-making processes for the confirmation of infection by ISA virus, with virus isolation in cell culture leading to confirmation of the infection, regardless of the state of disease on a farm. At that time the procedure adopted for diagnosis of ISA in Scotland, supported by the Final Report of the Joint Government/Industry Working Group on Infectious Salmon Anaemia in Scotland (2000), was that in adopting Council Directive 93/53/EEC, all of the following criteria needed to be satisfied to confirm the presence of ISA: clinical disease, typical macroscopic findings including evidence of anaemia, typical histological findings and evidence of infection.

6.     In May 2001 the European Commission accepted a withdrawal scheme submitted by the UK (Scotland), in response to the European Commission amendment to Council Directive 93/53/EEC, requiring the development and approval of a withdrawal scheme for fish in Scottish farms infected with ISA (Commission Decision 2001/186/EC).

7.     In this UK (Scotland) scheme, the diagnosis of ISA would now reflect the Mission to Scotland opinion that the presence of ISA would be confirmed by either the isolation and identification of the ISA virus from any fish on the farm, or the presence of clinical signs and supportive laboratory tests (as described in the original Council Directive 93/53/EEC). However, where no recent mortalities or fish showing clinical signs of ISA were observed, no samples would be required. If weak or abnormally behaving fish were observed, but the clinical signs of ISA were not observed, however, samples could be taken at the inspector’s or veterinarian’s discretion. When ISA was detected (either by the isolation and identification of the ISA virus from any fish on the farm or the presence of clinical signs and supportive laboratory tests) the following factors would be taken into account in determining the appropriate process of withdrawal (note: in all cases restocking would not be allowed until the farm had been fallowed for 6 months):

    * the number of mortalities
    * their distribution across the farm
    * the rate at which mortality occurs
    * cause of mortalities
    * risks to neighbouring farms in the same water catchment area or coastal zone

8.     In the case of widespread mortalities, the farm would be required to immediately begin the process of withdrawal and disposal of all fish. However, in farms where there were no widespread mortalities, fish would only be required to be withdrawn from parts of the farm (i.e. cage, tank or pool) in which mortality had reached 0.05% of the fish contained per day. Nevertheless, withdrawal in accordance with this scheme would be intended to proceed in stages until the farm had been cleared of fish.

    On the 21 June 2001, Council Decision 2001/186/EC (regarding the Scottish withdrawal scheme) was amended to include England, Scotland and Wales.

Scottish Executive Legislation concerning ISA

10.     In Scotland, Council Directive 91/67/EEC is implemented in the UK through The Diseases of Fish (Control) Regulation 1994.

11.     A new Code of Practice on Infectious Salmon Anaemia was produced in August 2000 to avoid and minimise the impact of Infectious Salmon Anaemia, arising from the Joint Government/Industry Working Group on ISA, including the possibility of a range of biological vectors of ISA.

12.     A report into the cause of the outbreak of ISA in 1998 was published by the Fisheries Research Services in April 2001. The report was unable to identify the origin of the outbreak; however it was narrowed down to either the virus being introduced accidentally on a well boat from infected areas in Norway, or from a wild reservoir.

Industry Concerns

13.     Concerns have been raised about the impact on the Scottish salmon industry of the scheme categorising a farm as having the disease, when evidence for infection has been based on the isolation and identification of the ISA virus from any fish on the farm, without any clinical signs of the disease. In particular concerns have been raised about the accuracy of the viral test methods (and risk of false positive results), and the prevalence of the virus in the wild with the possibility of routine viral infection of farmed fish from wild populations at levels which don’t cause the harmful clinical disease. Once a farm has been designated as infected, all fish will eventually have to be withdrawn and the site disinfected and left fallow for 6 months. There is, however, no compensation for any lost income by farmers as a result of this process.

    Following an outbreak of ISA in May 1998, the Scottish Office, in September 1999 introduced a fund of up to £9 million over three years to provide assistance to individual farmers who face losses caused by ISA. This was approved by the European Commission on 30 May 2000 and was to be administered by Highlands and Islands Enterprise.

15.     On 23 June 2000 the European Parliament noted that they were of the opinion that the Scottish salmon industry faced an ongoing crisis which would become more severe if no remedial action was taken. It called for the addition of ISA in the list of diseases provided for by Council Decision 90/924/EEC and for funding to be provided for research into a vaccine against ISA.

16.     On 16 November 2000 the Scottish Parliament European Committee asked the Scottish Executive and European Commission to re-examine financial support for salmon farmers and to reclassify the types of fish disease which qualify for funding assistance under Decision 90/424, and to explain why Norway does not follow the regime imposed on Scotland and the rest of the EU.

17.     On 21 September 2001 the advocate general of the European Court of Justice gave the opinion that salmon farmers had no right to compensation for fish slaughtered during the outbreak of infectious salmon anaemia in the late 1990s. The case was brought against the Scottish Executive by the fish farming companies Hydro Seafood and Marine Harvest. It is now up to the full court to decide whether to accept this view.

Notes for Editors

1. Sir Roderick MacSween, Chairman of the Working Party is Emeritus Professor of Pathology at The University of Glasgow. He is a past President of The Royal College of Pathologists and was Chairman of The Academy of Medical Royal Colleges. Sir Roderick is married, with two children and one grandson.


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