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Surveillance of Fish Diseases in the Nordic Countries
Acta Veterinaria Scandinavica volume 42, Article number: S43 (2001)
Due to the increasing importance of disease problems in the fish farming industry and the impact disease may have on both feral and farmed fish in the Nordic countries, monitoring and surveillance on diseases have for many years been considered to be of socioeconomic importance. All the Nordic countries have a national legislation as basis for their surveillance and disease control in aquatic animals and regulations listing notifiable diseases of concern to the countries. The list of diseases vary between the countries. In addition, Denmark, Finland and Sweden are ruled by  as regards placing on the market of aquaculture animals and products. The surveillance for viral diseases in all the Nordic countries has mainly been based on the testing procedures given in the EU Commission .
The list of diseases to be monitored or surveyed for varies between the Nordic countries. All the Nordic countries run a surveillance programme for Viral Haemorrhagic Septicaemia (VHS) and Infectious Haematopoietic Necrosis (IHN) based on EU regulations and a monitoring programme for Infectious Pancreatic Necrosis (IPN) on a national level. Iceland and Norway have also established a surveillance programme for Viral Nervous Necrosis (VNN) on a national level, while Finland and Sweden has established a surveillance programme for Spring Viraemia of carp (SVC) on a national level in order to obtain additional guarantees within the EU for that disease. Norway is the only country that has established a control programme for Herpesvirus scophthalmi in turbot, for Anguillicola spp in eel and for pasteurellosis in sea bass. These programmes are due to start year 2000. Monitoring of Bacterial Kidney Disease (BKD) takes place in all the Nordic countries; in some of the countries it is being compulsory and in others it is carried out on a voluntary basis. Due to the importance of the haptorworm Gyrodactylus salaris for wild stocks of Atlantic salmon, a surveillance programme for this parasite is under consideration in Norway, while in Finland regular monitoring for the parasite takes place in certain regions recognised to be free of the parasite in order to obtain additional guarantees within the EU. Similarly, Finland, Iceland and Sweden run a national control programme for furunculosis for the same reason and Finland has asked for additional guarantees for certain areas in which the disease do not occur.
The measures taken when disease occur vary from restrictions on movements to stamping out procedures as well as disinfection procedures and other means to establish control of a disease. The ultimate goal is to eradicate or keep the level of disease to a minimum.
On a global scale, fish and fishery products are the main food supply for human beings and these products constitutes more than 80% of the total amount of seafood consumed. It is widely known that the supplies of fish from traditional fisheries are more or less constant  and that the shortage in fish and fish products has to be met by aquaculture. The potential for the aquaculture industry to meet the challenge as regards food security has been clearly demonstrated by the rapid expansion of the fish farming industry world wide . Fig. 1 shows the development of aquaculture compared to global fisheries in the period 1987–1997 (FAO). The figures show that the total capture in fisheries is relatively constant at some 90 millions metric tonnes while there has been an increase in aquaculture production from 10 millions metric tonnes to 28 millions metric tonnes in the same period.
The way fish farming is conducted and the species farmed vary considerably in the world depending on geographical conditions, water resources, temperature etc.
Fish farming in the Nordic countries
In the Nordic countries, the fish farming industry is mainly based on salmonid species, Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss), but in the later years several different marine species such as halibut (Hippoglossus hippoglossus), turbot (Scophthalmus maximus) and sea bass (Dicentrarchus labrax) have gained increased importance.
Table 1 gives an overview over the fish species farmed in the Nordic countries as well as the size and production of these species.
The rational for disease surveillance
Over the last decades, several emerging or serious diseases in fish have been diagnosed in farmed and feral populations, creating large problems in the fish farming industry and thus being the subject of surveillance and monitoring programmes in many countries . The differences between infectious diseases in fish and those of terrestrial animals means that the approach to the problems and the eradication efforts differ as the diseases may spread effectively through flowing water .
Following is the described basis for and the results of monitoring and surveillance programmes as well as established measures on some of the diseases considered to be of major concern in the Nordic countries.
Basis for the monitoring and surveillance in the Nordic countries
All the Nordic countries have a national legislation as basis for their surveillance and disease control in aquatic animals, as well as regulations listing notifiable diseases of concern to the countries. The list of notifiable diseases vary from country to country. In addition to their national legislation, Denmark, Finland and Sweden are ruled by  as regards placing on the market of aquaculture animals and products, but even Iceland and Norway have accepted the principles laid down in the Directive.
The monitoring and surveillance for viral diseases in all the Nordic countries has mainly been based on the testing procedures given in the EU Commission  while for the bacterial and parasitic diseases, standard diagnostic procedures for such diseases has been used for screening purposes.
The list of diseases under monitoring and surveillance varies between the Nordic countries. All the countries runs a surveillance programme for Viral Haemorrhagic Septicaemia (VHS) and Infectious Haematopoietic Necrosis (IHN) based on EU regulations  and a monitoring programme for Infectious Pancreatic Necrosis (IPN) on a national level. The Nordic countries have also a clinical monitoring for infectious salmon anaemia (ISA) as no valididated surveillance methods so far have been established. Iceland and Norway has also established a surveillance programme for Viral Nervous Necrosis (VNN) on a national level, while Finland and Sweden have established a surveillance programme for Spring Viraemia in carp (SVC) on a national level in order to obtain additional guarantees within the EU for that disease. Norway is the only country that have established a control programme for Herpesvirus scophthalmi in turbot, for Anguillicola spp in eel and for pasteurellosis in sea bass which will start year 2000.
Monitoring for Bacterial Kidney Disease (BKD) takes place in all the Nordic countries; in some of the countries being compulsory and in others carried out on a voluntary level.
Due to the importance of the haptorworm Gyrodactylus salaris for wild stocks of Atlantic salmon, a surveillance programme for this parasite is under consideration in Norway, while in Finland regular monitoring for the parasite takes place in certain regions recognised to be free of the parasite to obtain additional guarantees within the EU. Similarly Finland, Iceland and Sweden runs a national control programme as regards furunculosis for the same reason and Finland has asked for additional guarantees for certain areas in which the disease due not occur.
Aim of surveillance
The aim of the monitoring and surveillance programmes for fish diseases in question in the Nordic countries is either to document and maintain freedom of disease, to eradicate a disease or to keep a disease under control within certain bonds. For some of the diseases that may be present on a low level such as IPN in Finland and Sweden, the ultimate aim will probably be eradication.
Surveillance programmes and target populations
The main target population for the monitoring and surveillance programmes is salmonids for most of the diseases under surveillance.
The size of the target populations is given in Table 1. All types of farms are included in the survey such as hatcheries, brood stock farms as well as grow out farms, table 2 shows the diseases under surveillance and the target species for the disease in question.
Denmark, Norway and Scotland run a surveillance programme with the aim of deriving information on VHS virus and other viral infections in wild marine populations is carried out in European coastal waters from the English channel in the south to the Spitsbergen area as well as in the Baltic sea [9, 12]. Similar examinations were carried out by Sweden in the Baltic sea and Kattegat in 1998 and the beginning of 1999.
The basis for the different surveillance and monitoring programmes in formal terms is partly based on EU regulations, OIE criteria or criteria derived from national legislation. For some of the diseases such as IHN and VHS, the participation is compulsory in all the Nordic countries as regards approval and maintenance of disease free status for the two diseases either for the whole country, for zones or for farms in non approved zones. In Denmark a control program for VHS started as early as in 1965, while in Finland, Iceland, Norway and Sweden an official surveillance program started in 1995, 1993, 1994 and 1993 respectively. For other diseases such as furunculosis the participation is compulsory in some countries such as Sweden, while it is voluntary or even non existing on a regular basis in other countries such as Norway.
In Finland, the surveillance programme for G. salaris has been compulsory for the last three years.
The sampling of fish for surveillance vary between the Nordic countries depending on the infrastructure of the health control in the different countries. In Sweden the National Fish Health Service (Fiskhälsan FH AB) are responsible for all sampling, while in Norway, the responsible Authorithy is the district veterinary officers (DVO) or local fish health services operating under instruction of the DVO. In Finland the municipal veterinarians do the necessary sampling when inspecting the farms which is done biannually.
In Iceland, the responsible authority as regards sampling is under the supervision of the Veterinary Officer for Fish Diseases.
In Denmark, the Danish Veterinary and Food Administration do the necessary sampling and control.
Analyses of the diseases under surveillance are carried out at official veterinary laboratories i.e. National Veterinary Institute in Norway and Sweden, the Veterinary Officer for Fish Diseases, Keldur, in Iceland, Danish Veterinary Laboratory in Denmark and National Veterinary and Food Research Institute (EELA) in Finland.
Test and testing procedures
The surveillance for viral diseases in all the Nordic countries has mainly been based on the testing procedures given in the EU Commission . According to the decision, fish farms are inspected clinically biannually and samples for virological examinations are collected by rotation in 50% of the fish farms each year to document freedom for IHN and VHS. In Denmark, Finland, Iceland and Sweden, all or some of the same samples are used for IPN testing. In Denmark, the control of IPN is based on the monitoring of IPN free broodstock farms and ongrowing farms as IPN is considered to be endemic in non controlled farms. In Norway testing for IPN virus is done in a specific monitoring programme in brood stocks of Atlantic salmon and rainbow trout as IPN virus neutralisation is used in the examinations for IHN/VHS virus.
The examination procedures given in the  are the basis for examinations as regards BKD, Gyrodactylus salaris and VNN while for furunculosis, pasteurellosis and Anguillicola spp, standard bacteriological or parasitological procedures are used, respectively. The frequency in the testing of these diseases is varying between the countries.
Measures taken when positive diagnosis occur
In all the Nordic countries, it is the Veterinary Authorities that is responsible for the implementation of measures that will be used in order to control a given notifiable disease. The implementation involves both central and regional veterinary officers.
In all the Nordic countries except non-approved zones in Denmark, stamping out procedures followed by cleaning, disinfection and fallowing will be carried out if VHS is diagnosed [11, 13]. In non-approved zones in Denmark, a stamping out program will be started if 1/3 of the farms in a river system agrees to an eradication program to get rid of the disease.
Since IHN and SVC is considered to be absent in all the Nordic countries, stamping out procedures will be applied to these diseases. As regards IPN, the detection of the disease or the virus as such, will be subject to restrictions followed by a sanitation programme laid down by the Board of Agriculture in Sweden, while in Norway the mere detection of IPN virus will not bring about any restrictions. Clinical IPN will, however, lead to restrictions on movement of live fish in Norway as long as mortality and signs of the disease occur. In Finland, isolation of IPN virus will lead to restrictions on movement of live fish in continental zones, while clinical IPN probably will result in more strong measures. These have so far not been determined. Prevention may be achieved by avoiding introduction of disease free eggs and/or fish into disease free farms as well as using protected water supply (e.g. spring-, borehole water).
In Iceland, detection of furunculosis is also followed by stamping out because the disease is recognised as a List A disease, while in Sweden active measures are taken only if the disease occur in freshwater, but not in sea water where the disease is considered to be enzootic. In Norway, restrictions are laid upon farms if the furunculosis is diagnosed. Hatcheries are not allowed to sell live fish while affected fish farms in sea water may keep the fish until reaching marketable size for slaughtering.
In all the Nordic countries an infected farm may restock after fallowing if no signs of infection appear after a sanitation programme has been carried out.
In Sweden, all expenses will be paid by the Board of Agriculture for IHN, VHS, SVC and IPN as these diseases are included in the epizootic act. Similarly, in Finland, the government will pay for all expenses if IHN and VHS are detected, probably also for SVC. In Norway affected farm(s) will have to pay themselves for any measures imposed by the authorities for the time being, because no compensation is granted.
In Denmark expenses will probably be paid in case of IHN and ISA outbreaks and in case of a VHS outbreak in approved zones free of VHS, expenses might be covered as well.
Health certificates and/or transportation documents is needed in connection with deliveries of live fish for stocking into grow out farms and restocking into rivers. Additionally, in Norway it is not allowed to move fish prior to slaughter, when they are stocked in a sea water site. This is to prevent spread of disease if disease occur.
In all the Nordic countries, the record of findings are kept by the responsible authorities, both regionally and centrally. The diagnostic laboratories also keep the necessary documentation on the examinations carried out. Furthermore all farms have to keep records on events in the farms that can be requested by Competent Responsible Authorithy.
While still a few cases of VHS is diagnosed in Denmark each year, Finland, Iceland, Norway and Sweden are considered to be free from VHS. However, VHS was diagnosed in one farm in Norway and Sweden in 1998. All Nordic countries have status as free from IHN and SVC although only Finland and Sweden is carrying out a specific surveillance programme for SVC.
IPN is considered to be the main viral disease problem in Norway. The disease is endemic in Denmark but not considered as a mayor problem. The disease level of IPN is low in Finland and Sweden and so far not reported in Iceland. Iceland is considered to be free from classical furunculosis, while the disease appears to be endemic in Denmark, Finland, Norway and Sweden. However, some areas in Finland are reported free of furunculosis and the authorities has established so-called protective zones to which live fish and fish eggs only can be transported if special permission is granted.
BKD has been reported from all the Nordic countries but the level appear to be relatively low [5, 8]. In Iceland. the disease has occasionally been detected in wild Atlantic salmon returning to spawning grounds while it has not been detected in farms for the last 4 years. BKD was for the first time detected in wild salmon in the Baltic sea in 1999, so it is quite apparent that a reservoir of the disease exists in the wild.
Gyrodactylus salaris has been described from Denmark, Finland, Norway and Sweden, but it is only in Norway that disease caused by this parasite has given high mortality in feral fish populations in Norway. The parasite has now totally been detected in 40 rivers and 37 farms/hatcheries since its first detection.
Anguillicola crassus has so far been reported from Denmark, Norway and Sweden, but the distribution in the wild is not known.
Although some differences occur, all the Nordic countries have established appropriate surveillance and monitoring for fish diseases of concern to the fish farming industry. Due to these systems and good management practises, the fish disease situation in the Nordic countries is generally good compared to other countries in the world.
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Håstein, T., Hellstrøm, A., Jonsson, G. et al. Surveillance of Fish Diseases in the Nordic Countries. Acta Vet Scand 42, S43 (2001). https://doi.org/10.1186/1751-0147-42-S1-S43
- Atlantic Salmon
- Surveillance Programme
- Nordic Country
- Notifiable Disease
- Fish Disease