Conf. OIE 2000, 27-49

PRINCIPLES OF PREVENTION AND CONTROL OF AQUATIC ANIMAL DISEASES

Tore Håstein Department of Aquatic Animal Health - Regional laboratories, National Veterinary Institute P.O. Box 8156, DEP, 0033 Oslo, Norway

Original: English

SUMMARY: In order to prevent or reduce the risk of introduction of serious aquatic animal diseases and thus avoid economic losses in the aquaculture industry and in wild stocks, it is important to have a set of principles for the prevention and control of such diseases. These principles include the establishment of a legislative framework, both nationally and internationally. The key international documents are the OIE International Aquatic Animal Health Code and Diagnostic Manual for Aquatic Animal Diseases, as well as other documents such as EC Directive 91/67/EEC, which applies health regulations to all European Union countries. Currently, guidelines for management of diseases in Asia are being established by FAO1/NACA2, partly based on the OIE standards. This report describes in detail the most important factors involved in the prevention and control of aquatic animal diseases. These factors include, in addition to a legislatory framework, 1) listing of diseases, 2) procedures for inspection and control, 3) import regulations, 4) quarantine measures, 5) procedures for the introduction of new species, 6) transport regulations and restriction on movements, 7) disinfection procedures, 8) contingency plans, 9) training of personnel, 10) disease prevention at the aquaculture establishment level as regards water treatment, vaccination, medical treatment, as well as hygienic and sanitary. The results of a questionnaire that was sent to the OIE Member Countries showed that there are considerable differences among the countries regarding the various principles considered for disease prevention and control of aquatic animal diseases. Twelve of the responding countries (17%) do not have any established regulations on aquatic animal diseases. It is recommended that some controls should be put in place using existing national and international regulations but adapting these to suit national requirements and conditions in aquatic animal health.

1. INTRODUCTION During the 67th OIE General Session, the International Committee decided that, due to the increasing socio-economic importance of aquaculture and the impact of diseases in aquatic animals world-wide, one of the technical items for the 68th General Session should be a presentation of a report on the ‘Principles of prevention and control of aquatic animal diseases’. To facilitate this report, a questionnaire on topics of importance regarding principles of prevention and control of aquatic animal diseases was sent to all the 155 OIE Member Countries. Seventy-one questionnaires were completed and returned to the OIE (see Appendix 1 for list of responding countries) and the information given has been incorporated into this report. Similar issues were presented at the meeting of the OIE Regional Commission for Europe in 1996 (24) and at the meeting of the OIE Regional Commission for Asia, the Far East and Oceania in 1999 (41). In this paper, some basic information on the importance of aquaculture as well as the basic principles for prevention and control of aquatic animal diseases will be discussed.

1 2

Food and Agriculture Organization of the United Nations Network of Aquaculture Centres in Asia-Pacific

- 27 -

Conf. OIE 2000

On a global scale, fish and fish products constitute the main protein supply for human beings, and these products make up more than 80% of the total amount of seafood consumed. As supplies of fish from traditional fisheries remain constant (FAO Aquaculture Statistics), the shortage in fish and fish products has to be met by aquaculture. Aquaculture production is thus increasing in importance. The growth in production has been remarkable over the past ten years and this growth rate is continuing. For example, the production of fish and shellfish in 1997 reached some 28.808 million metric tons, of which approximately 90% (25.852 million metric tons) came from Asian countries. 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 (48). In Figure 1, the amount of aquaculture production compared with production from capture fisheries is shown. The figure shows 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 million metric tonnes in 1987 to 28 million metric tonnes in 1997, a growth of more than 10% per year.

Fig. 1 - Aquaculture and global fisheries production*

Million metric tonnes

140 120 100 80

Total aquaculture

60

Total capture

40

Total world fisheries

20

* FAO information

1997

1996

1995

1994

1992

1990

1989

1988

1987

0

Year

Fish are the most important farmed aquatic animal species compared with the production of molluscs and crustaceans. Farming method and species farmed vary considerably throughout the world depending on the geographical conditions, water resources, temperature, etc. According to information received, molluscs represent 23.8% of the global aquaculture production, and three mollusc species have been ranked among the top ten world cultured species. The Pacific cupped oyster Crassostrea gigas is ranked No. 2 in value and volume, while the Yesso scallop, Pecten yessoensis and the carpet shell Ruditapes phillipinarum are ranked 7, 8 and 9 in volume. Table 1 gives an overview of the main aquatic animal species farmed in OIE Member Countries responding to the survey. Due to the high densities of single species in the holding units in marine and freshwater farms, the prevalence and spread of disease in aquatic animal populations has increased. Efforts must be made to prevent the occurrence and spread of aquatic animal diseases, as well as to reduce losses should diseases occur. As for mammals, birds and bees, the main disease problems in aquaculture are caused by a wide range of infectious organisms, including bacteria, viruses, fungi, protozoan and metazoan parasites. Nutritional and environmental problems (i.e. toxic algal blooms) also occur. The diseases spectrum may vary a great deal on a global basis depending on the farming conditions, aquatic animal species, climatic and environmental conditions, and distribution of infectious agents within different regions of the world (22). Disease prevention and control is therefore of great importance, both for the individual farmers as well as for the national economy of some countries (12). Different management practices have therefore to be considered. In a broad sense, management practices can be defined as comprising not only husbandry methods and precautionary steps taken on the farm, but also the legislative measures on which these are often based. Regulatory measures will therefore necessarily be the most important consideration for prevention and control of aquatic animal diseases.

- 28 -

Conf. OIE 2000

Table 1: Aquatic animal species reported to be farmed in OIE Member Countries according to answers to the questionnaire Aquatic animal species

Country in which one or more of the species indicated have been farmed

Atlantic salmon/Pacific salmon spp.

Australia, Canada, Denmark, Estonia, Finland, Iceland, Japan, New Zealand, Norway, Spain, Sweden, United Kingdom,

Rainbow trout, brown trout, sea trout, brook trout, char, Argentina, Austria, Belgium, Bosnia and Herzegovina, Bulgaria, Canada, whitefish Colombia, Croatia, Cyprus, Czech Rep., Denmark, Estonia, Finland, Germany, Greece, Iceland, India, Israel, Italy, Japan, Korea (Rep. of), Kyrgyzstan, Luxembourg, Netherlands, Norway, Peru, Poland, Russia, Slovakia, Spain, Sweden, Switzerland, Turkey, Ukraine, United Kingdom, Zimbabwe Carps, carp hybrids (bighead carp, grass carp, mirror carp, silver carp)

Algeria, Austria, Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, China (People’s Rep. of), Croatia, Cuba, Czech Rep., Estonia, Germany, Guatemala, Hungary, India, Israel, Italy, Japan, Jordan, Korea (Rep. of), Kyrgyzstan, Laos, Luxembourg, Nepal, Paraguay, Poland, Romania, Russia, Saudi Arabia, Slovakia, Sri Lanka, Syria, Thailand, Ukraine, Vietnam

Catfish (Clarias spp., Pangasius spp., Silurus spp.)

Angola, Bulgaria, Ghana, Italy, Jordan, Netherlands, Saudi Arabia, Sudan, Thailand, Ukraine

Sea bass

Algeria, Croatia, Cyprus, Greece, Iceland, Italy, Korea (Rep. of), Malaysia, Malta, Morocco, Singapore, Spain, Turkey

Sea bream/sharpsnout seabream, red sea bream

Croatia, Cyprus, Greece, Israel, Italy, Japan, Korea (Rep. of), Malta, Morocco, Spain, Turkey, Ukraine

Tilapia

Angola, Argentina, Chad, Colombia, Ghana, Guatemala, Guyana, Israel, Jordan, Laos, Malaysia, Paraguay, Saudi Arabia, Senegal, Singapore, Sri Lanka, Sudan, Syria, Thailand, Zimbabwe

Eel

Algeria, Belarus, China (People’s Rep. of), Estonia, Italy, Japan, Korea (Rep. of), Netherlands, Ukraine

Ayu

Japan

Bream, black seabream (pollan)

Belarus, Kyrgyzstan, Ukraine

Cod

Norway

Grouper

Malaysia, Saudi Arabia, Singapore, Vietnam

Halibut, turbot

Iceland, Norway, Spain, United Kingdom

Japanese green flounder

Japan, Korea (Rep. of)

Japanese horse mackerel

Japan

Mullet

Algeria, Israel, Italy

Ornamental fish (gouramy, guppy, swordtail, molly, neon tetra, discus, goldfish, dragonfish)

Singapore, Thailand

Pike, pikeperch

Belarus, Belgium, Estonia, Russia, Ukraine

Puffers (Tetraodontidae)

Japan

Rabittfish

Saudi Arabia

Snakehead

Singapore, Thailand

Snapper, golden snapper

Malaysia, Singapore

Sturgeon

Italy, Ukraine

Tench

Austria, Czech Rep., Ukraine

Tuna

Australia, Croatia

Yellowtail

Japan, Korea (Rep. of)

Other indigenous species/species not indicated

Laos, Malawi, Thailand

- 29 -

Conf. OIE 2000

Oysters (Crassostrea spp.)

Australia, Korea (Rep. of), New Caledonia, New Zealand, Senegal, Spain, Sudan, United Kingdom,

Pearloysters

Australia, Iran

Clams, green mussels, mussels, scallop

Canada, Italy, Korea (Rep. of), Malaysia, New Zealand, Peru, Singapore, Spain, United Kingdom

Shrimp/prawn (Penaeus spp., Machrobranchium spp., Mesopenaeus spp.)

Argentina, Australia, China (People’s Rep. of), Colombia, Guatemala, Guyana, India, Iran, Japan, Korea (Rep. of), Malaysia, New Caledonia, Peru, Saudi Arabia, Senegal, Singapore, Sri Lanka, Taipei China, Turkey, Vietnam

Crayfish, cherax

Argentina, Azerbaijan, Estonia, Finland, Iran, New Caledonia

Langosta, lobster, mittencrab,

China (People’s Rep. of), Guatemala, Peru, Singapore, Vietnam

Turtles

China (People’s Rep. of)

Abalone

Australia, Iceland

It must be emphasised that the environment in which the aquatic animals live usually harbours a varied microflora that may include different types of pathogens. Nevertheless, the mere presence of a disease organism in the environment of an aquaculture establishment to which aquatic animals are exposed does not necessarily mean that a disease condition will arise, as good management practices may be sufficient to prevent outbreak of clinical disease. On the other hand, bad management may result in disease outbreaks and mortality due to opportunistic agents. In order to maximise the ability to withstand disease, it is of the utmost importance to maintain optimal environmental conditions such as stocking densities, good water quality, proper feeding, and high standards of hygiene, as well as paying attention to the possibility of involuntarily selecting disease-resistant animals and implementing disease surveillance and control systems (health plans) for aquatic animals. The success of such efforts, however, will depend to a large extent on the personnel responsible for carrying out daily routines on the farm. The main components of disease prevention and control may be summarised as follows: •

Legal basis for disease control in aquatic animals

•

Highly qualified personnel to carry out the work at the aquaculture establishment, laboratory level and administrative level

•

Stocking programmes and management practices to avoid disease outbreaks

•

Disease prevention techniques to avoid the introduction of pathogens into a population on the farm

•

Control measures if disease occurs

•

Eradication of certain diseases (pathogens) from a facility and, if possible, from wild stocks

Thus, any disease prevention and control system for aquatic animals requires a satisfactory legal framework plus a Competent Authority with the necessary powers for policy decision-making, and for the practical application of regulations that are accepted by the aquaculture industry. It is impossible to cover in detail all aspects of prevention and control of diseases in aquatic animals due to the vast number of different aquatic animal species and diseases in each species that may call for specific solutions. However, some major principles will be discussed with special emphasis on fish, as fish farming remains the most widely found form of aquaculture and thus has the most important socio-economic impact world-wide.

2. BASIC PRINCIPLES FOR PREVENTION AND CONTROL 2.1.

Legislative framework Outbreaks of transmissible aquatic animal diseases can in many cases be traced back to the movement of aquatic animals and their introduction into new areas. In order to prevent and control disease in aquatic animals through management practices, it is necessary to have an established legal framework that can be used as a tool to avoid the introduction and spread of serious aquatic animal diseases, both at the national and international level (5, 20, 30, 43, 45, 56). Once a disease has become - 30 -

Conf. OIE 2000

established in a free-living population or under farming conditions, the possibility of it subsequently spreading to other farms, zones, regions and countries via water, by trade, etc., is significant. This poses a constant risk to the aquatic animal industry despite the fact that successful emergency eradication programmes have been reported (27). The importance of a sound legislative framework is thus clearly demonstrated. An optimal legal framework must include measures that give the necessary regulatory control to avoid the introduction of serious transmissible diseases into a country, to prevent transmission within a country, and to prevent and control disease if introduced. The legal provisions must include a wide range of steps such as: •

Listing of notifiable diseases exotic to and/or of socio-economic importance to that country

•

Defined procedures for dealing with outbreaks of notifiable diseases, including contingency plans, zoning principles, epidemiological studies, eradication procedures (i.e. stamping-out), sanitary slaughtering, handling of carcasses, disinfection, fallowing, restocking, etc.

•

Clearly defined procedures for inspection, health control and disease prevention

•

Import/export regulations

•

Quarantine measures

•

Regulations concerning the introduction of new non-indigenous aquatic animal species

•

Transport regulations

•

Controls on the movement of live aquatic animals from farms or areas affected by serious disease and the marketing of such animals for human consumption

•

Sanitation and disinfection procedures of intake/outlet water, aquaculture premises, equipment, processing plants, wastes, etc.

The statutory definition of an action to be taken is one of the most important legal steps for disease control in aquatic animals and may have tremendous implications for on-farm management practices aimed at disease control. However, there is usually little that can be done as regards disease incidences in wild stocks. Of the OIE Member Countries responding to the questionnaire, 59 reported that they had established regulations for aquatic animal diseases, while 12 countries had no regulations. Countries with no legislation for aquatic animal diseases, should try to establish them in the near future. As regards the responsibility for the legislatory framework in the Member Countries, the responses showed that this responsibility could be divided into four different categories: •

Veterinary Administration

•

Competent Authority other than the Veterinary Administration

•

Responsibility shared by different Competent Authorities

•

No responsible Authority

In 41 (58%) of the responding Member Countries, the Veterinary Administration was in charge of legislation for aquatic animal diseases, while the figures for other Competent Authority, shared responsibility between Authorities and no responsible Authority were 17 (24%), 10 (14%) and 3 (4%), respectively. 2.2.

List of notifiable diseases As mentioned previously, a wide variety of different diseases have been described in aquatic animals. Not all diseases are of the same importance, and a disease problem in one country may not be recognised as a problem in another country. It is thus necessary to establish lists of notifiable diseases both on a national and international level either because they are exotic to a country, have limited distribution, can be transferred by trade, or have a serious impact on farmed and wild aquatic animals. Forty-six (64.8%) of the 71 responding countries reported that they had a disease notification system and 43 countries (60.5%) had established a list of notifiable diseases. Some of these countries have a large number of diseases listed while others had only a few (Tables 2, 3 and 4). - 31 -

Conf. OIE 2000

Table 2: Major notifiable fish diseases reported by one or more of the OIE Member Countries responding to the questionnaire Virus

Bacteria

Fungus

Parasites

Channel catfish virus disease (CCVD)

Bacterial kidney disease (BKD) Renibacterium salmoninarum

Branchiomyces infection (Branchiomyce spp.)

Gyrodactylus spp.

Epizootic haematopoietic necrosis (EHN)

Colibacillosis

Epizootic ulcerative syndrome (EUS)

Proliferative kidney disease

Erythrocytic inclusion body syndrome (EIBS)

Enteric septicaemia (Edwardsiella ictaluri)

Ichthyophonus hoferi infection

Ligulosis

Herpesvirus infection

Red pest disease (Edwardsiella tarda)

Saprolegnia spp.

Philometrosis

Infectious hematopoietic necrosis (IHN)

Infection with atypical Aeromonas salmonicida

Myxobolus cerebralis (whirling disease)

Infectious pancreatic necrosis (IPN)

Furunculosis (Aeromonas salmonicida subspecies salmonicida)

Lentosporidiosis

Infectious salmon anaemia (ISA)

Infection with Mycobacterium spp.

Diphyllobothriosis

Oncorhynchus masou virus disease (OMV)

Pasteurellosis (Pasteurella piscicida)

Ceratomyxa shasta

Pancreas disease (PD)

Piscirickettsiosis (Piscirickettsia salmonis)

Ichthyophthiriasis

Rhabdovirus infections

Streptococcosis (Streptococcus spp.)

Henneguya salmincola

Spring viraemia in carp (SVCD)

Cold water vibriosis (Vibrio salmonicida)

Kudoa thyrsites

Viral erythrocytic necrosis (VEN)

Vibriosis (Vibrio anguillarum)

Loma salmonea

Viral haemorrhagic septicaemia (VHS)

Yersiniosis (Enteric red mouth)

Enterozytozoon

Viral nervous necrosis (VNN)

Anchor worm

Table 3: Major notifiable mollusc diseases reported by one or more of the OIE Member Countries responding to the questionnaire Virus

Parasites/protozoans

Iridovirosis

Bonamiosis (Bonamia spp.) Haplosporidiosis (Haplosporidium spp.) Marteiliosis (Marteilia spp.) Mikrocytosis (Mikrocytos spp.) Perkinsosis (Perkinsus spp.)

- 32 -

Conf. OIE 2000

Table 4: Major notifiable crustacean diseases reported by one or more of the OIE Member Countries responding to the questionnaire Virus

Fungus

Baculovirus midgut gland necrosis (BMN)

Crayfish plaque (Aphanomyces astaci)

Nuclear polyhedrosis baculovirosis (BP, MBV) Infectious hypodermal and haematopoietic necrosis (IHHN) Yellowhead disease (YHD) White spot disease (WSD) Taura syndrome

As can be seen from the tables, quite a few of the diseases are the same as the diseases listed in the OIE International Aquatic Animal Health Code (44). This indicates that either the OIE Member Countries agree as to which diseases should be recognised as serious or that the Member Countries have adopted the OIE listed diseases. However, if a system for categorisation of diseases could be established, then the OIE system for listing diseases will be even more appropriate. 2.3.

Procedures for inspection, control and certification It is necessary to have effective systems for aquatic animal disease surveillance and control to obtain evidence on whether a country or a region is free from a disease or a disease agent. Epidemiology is the basic method and requiring both active and passive surveillance for generating reliable results as regards the true disease status in a country/region (20). Active surveillance includes inspections and examinations of the farms of fish slaughter houses, as well as disease control in wild species. This latter requires knowledge of the mechanisms of spread as well as of the possible reservoirs of a given pathogen. Passive surveillance includes laboratory reports and other collected test results from research programmes, etc. (21, 26). Ideally, the responsibility for such work must rest with independent authorities with no direct economic interests in aquatic animal farming. Inspection and sampling on farms must be done by independent, trained personnel. On-site sampling and monitoring procedures should be carried out frequently, not just twice a year as is recommended in many countries and by the OIE. It is extremely important that inspection and health surveillance takes place immediately prior to the transfer of live aquatic animals or gametes from a farm site. This is of particular significance in connection with international trade, but is also relevant for movement between regions within a country as it will help to prevent transmission of pathogens. To achieve this, it is preferable to have a decentralised aquatic animal health infrastructure (veterinarians/other aquatic animal health officers) that is well established and functions locally in the regions where the aquaculture establishments are located, a competent laboratory system as well as a comprehensive, co-ordinated reporting system for diseases of concern. The reporting system must be run by the Competent Authorities responsible for health management in aquatic animals. Carey (pers. comm. 1996) suggested that the essential elements for a national fish disease surveillance programme should include: •

A mandatory system for reporting fish diseases of concern that are detected by health officers (veterinarians, biologists) or the fish farmers themselves and brought to the attention of the Competent Authority responsible for diseases in aquatic animals.

•

A national health monitoring programme with examination of susceptible species of wild and cultured stocks in order to obtain information on the occurrence of fish diseases/disease agents and/or transmission of diseases between farms/regions. Mandatory reporting of diseases/disease agents can be used as a source of information for the health monitoring programme.

•

A competent laboratory service carrying out diagnostic work using quality assured procedures that back up the field health service.

•

An established national/regional database for disease recording that can be used to identify and maintain disease free zones.

•

A register of fish farms in operation on a national level.

- 33 -

Conf. OIE 2000

•

Governmental authority to undertake emergency disease control measures. Coupled with this authority is a requirement for governments to identify compensation mechanisms for affected fish farms.

These points also cover mollusc and crustacean farming. Of the 71 countries responding to the questionnaire, 49 countries (69%) reported that they had established a system for inspection and certification of aquaculture establishments. 2.4.

Import regulations The spread of diseases between continents and between countries is usually related to movement of aquatic animals from one area to another, and a number of examples can be given on unwanted spread of disease (8, 13, 19, 47, 59). According to Bartley and Subasinghe (3), a number of pathogens introduced through import of exotic species have caused large economic problems in Asian aquaculture; these include Lerneae cyprinici, Myxosporidians, EUS, as well as several shrimp diseases of viral origin. In other parts of the world bonamiosis (17), crayfish plaque, Taura syndrome, IHHN and several other diseases have been reported to be spread by trade between countries and within countries (1, 33, 47). Losses in Thailand alone due to EUS and yellow head have been estimated at US$8.7 million (1982-1983) and US$30.6 million (1992), respectively (42, 54). Fifty-five (77.5%) of the responding countries reported that they had import regulations, and of these countries, 27 reported that they had experienced spread of disease by trade, but information was not given whether this was due to trade within or between countries. Table 5 gives an overview of the diseases that were reported to have been spread by trade.

Table 5: Diseases reported by the OIE Member Countries in the questionnaire to have been spread by trade* Fish diseases

Country

Virus Eel viruses (EVA, EVE, EVEX) Herpesvirus in catfish Herpesvirus in Koi carp Infectious haematopoietic necrosis (IHN) Infectious pancreatic necrosis (IPN) Infectious salmon anaemia (ISA) Spring viraemia in carp (SVC) Viral haemorrhagic septicaemia (VHS) Viral nervous necrosis (VNN)

Netherlands Italy Israel Belgium, Germany, Switzerland, Norway Norway Norway, United Kingdom United Kingdom Norway, Switzerland Croatia, Italy, Malta

Bacteria Atypical Aeromonas salmonicida Bacterial Kidney disease (BKD) Edwardsiella Flexibacter psychrophilus Furunculosis Pasteurella piscicida Pseudomonas anguilliseptica Streptococcus/Vagococcus spp. Vibrio damsela

Iceland Bulgaria, Finland, Norway, United Kingdom Thailand Israel Norway, Sweden Greece, Italy Netherlands Italy Italy

Fungus Epizootic ulcerative syndrome (EUS)

Nepal

Parasites Anguillicola crassus Anisakis spp. Dranculosis Gyrodactylus salaris Hexamita spp. Lernea cyprinici

Hungary, Netherlands Algeria, Belarus Belarus Norway Thailand Thailand

Crustacean diseases Virus Taura syndrome White spot disease

Colombia China (People`s Rep. of), Japan

* In the literature diseases other than those mentioned in the questionnaire have also been reported to be spread by trade.

- 34 -

Conf. OIE 2000

Import and export of live aquatic animals and live gametes of such animals between countries should thus be restricted, and prior to import, a risk analysis should be carried out. Ideally, imports of live material should only be accepted when necessary for the improvement of genetic material, for scientific purposes or if an introduction of an exotic species can be regarded as safe and of benefit to the importing country. Preferably gametes (eggs) only (and in small numbers) should be allowed in and accompanied by a valid international health certificate as indicated in the OIE Code. If possible, quarantine measures should be implemented. Molluscs are marketed live for human consumption, and this means that mollusc import is always risky because the animals must always be re-immersed. 2.5.

Quarantine measures Although not always easy, it is possible to carry out adequate quarantine measures in connection with the importation of aquatic animal larvae or gametes as the water volumes needed are limited, and may allow sufficient thermal or chemical disinfection of the water within acceptable economic limits. Unless numbers are small, quarantine measures for large numbers of older aquatic animals are difficult to carry out due to the large volumes of water involved. Forty-six countries (64.8%) reported that they had established quarantine measures in connection with imports.

2.6.

Introduction of new species According to Bartley & Subasinghe (3), introduction of new aquatic animal species into new areas, fish being the most important species, has been practised since the middle of the last century for the purpose of food production and a better income for the local society. Carp were introduced from Asia into Europe in the GreekRoman empire time for the same purpose (25). Such introductions may result in the transmission of ‘old’ and ‘new’ diseases to new regions. In addition, newly introduced species may be vulnerable to ‘local’ diseases already present. As awareness has increased of the risk of spreading disease, the impacts on native bio-diversity, and the economic consequences of adverse reactions, there has been a gradual decrease in such introductions. Introductions of mollusc species are very frequent, for example, the Pacific cupped oyster C. gigas, representing more than 95% of the world production, has been ranked in first place in terms of transfers and introductions (49) as recorded in the FAO/FIRI3 database. However, according to Grizel (16) none of the mollusc introductions has led to significant ecological disruption (17). In order to prevent such incidences, ICES4 have established guidelines for safe transfer of indigenous species (12, 28). It is, however, necessary to take adequate steps to minimise the risk. Both for farming and restocking purposes, it is important to have a restrictive policy towards the introduction of new species, and safe methods for the detection of latent carriers are needed. The scientific methods currently available are still not good enough in this respect. Bearing this in mind, regulations concerning introduction of new species have been established in 44 (62%) of responding countries.

2.7.

Transport regulations and restriction on movements Transport regulations and restriction on movements also form important legislative steps to limit the spread of disease within and between countries/regions. While restrictions on the movement of aquatic animals may be of significance in confining disease to a certain area, appropriate transport regulations can make it possible to direct movements of transport units for aquatic animals (lorries, wellboats, etc.) along routes that avoid regions with significant disease problems. Such regulations must also lay down appropriate procedures for the disinfection of the transportation units and equipment, stations for change of water, and handling of transport water when discharged. Transport regulations have been established in 43 of the countries responding to the questionnaire, but far more countries should address this issue.

3 4

FIRI: Inland Water Resources and Aquaculture Service ICES: International Council for the Exploration of the Sea

- 35 -

Conf. OIE 2000

2.8.

Disinfection procedures In addition to disinfection procedures for transport vehicles, it is also necessary to have officially enforced procedures for the disinfection of aquaculture establishments and slaughtering/processing plants. Disinfection procedures are also needed for fish/shrimp eggs. Such methods must of course be effective against pathogens, but it is also important that they pose no hazard to the operator or to the aquatic animals. It is beyond the scope of this paper to detail the procedures to be followed, but the principles are laid down in the OIE International Aquatic Animal Health Code. As two-thirds (51) of the Member Countries responding have established disinfection procedures to be used, this clearly shows that disinfection is regarded as extremely important for preventing and controlling disease/disease agents in aquatic animals.

2.9.

Handling of outbreaks of notifiable diseases/contingency plans The statutory definition of action to be taken when a notifiable disease is detected is one of the most significant legal steps for disease control in an aquatic animal farming area as well as on the individual farm, and may have tremendous implications for on-farm management practices aimed at disease control (9, 10). Depending on the categorisation and importance of a notifiable disease, different management practices may be laid down by law to achieve control over a disease situation. Such provisions may comprise rapid diagnosis, restriction on movements, complete slaughtering-out and destruction of all aquatic animals (stamping-out), partial stampingout procedures, as well as the introduction of sanitary slaughtering of fish, followed by disinfection and fallowing procedures. Arrangements for the handling of waste water, blood, and aquatic animal wastes are also important, as are measures to improve farm installations before new aquatic animals are introduced into an area/farm. It may be necessary to have alternative sites available throughout the redevelopment period to ensure satisfactory hygiene during the period when both infected and non-infected localities are in operation at the same time in the same area. This includes the collection of dead aquatic animals as well as the implementation of hygienic operating procedures to be followed by the personnel working on infected and non-infected sites, as well as visitors from outside. Visitors should not be allowed access unless there is good reason, and then only when specific precautions are taken, such as the use of rubber boots, pull-on coats, etc., which should be supplied by the farm. Forty-one of the responding countries (58%) reported that a contingency planning system was in place.

2.10. Training It is of utmost importance to have an aquatic animal health infrastructure able to provide an early warning system for disease reporting based on a skilled and experienced aquatic animal health service that carries out reliable diagnostic services and disease surveillance on a regular basis on the farms. In order to achieve these goals, a set of well-trained specialists who know how to deal with any disease emergency is needed. A good infrastructure within a country, nation and/or region (local) should be established and include diagnostic services and administrative expertise (disease experts, diagnostic laboratories, personnel qualified in aquatic animal diseases and personnel in administrative positions on aquatic animal diseases). Lists containing the names and addresses of all aquatic animal health personnel and diagnostic laboratories that may be involved in implementation of disease surveillance and emergency disease outbreak control in a country should be at hand. With good infrastructure, it is relatively easy to implement actions on any unknown disease outbreak. In order to achieve a good system on all levels, it is necessary to have highly qualified personnel involved in the different aspects of aquatic animal health, and the basis for this is education of the personnel. Both basic training and post-graduate training is necessary as new diagnostic methods are being developed (diagnostic kits, etc.). It is thus important that aquatic animal health issues be included in the curriculum of veterinary schools and universities in order to meet the increasing demand for qualified personnel. Forty-five of the Member Countries (63.4%) report that basic training is established in their respective countries, while others send their students to foreign countries in which appropriate education is given.

- 36 -

Conf. OIE 2000

2.11. Disease prevention at the aquaculture establishment It is important to maximise the ability of cultured aquatic animals to withstand disease as well as to minimise their exposure to pathogens, thus diminishing the risk of outbreaks of disease. In addition to the legal framework for disease control management, several on-the-farm factors are of great significance for the achievement of such goals. a) Site selection An aquaculture establishment should, ideally, be located and organised in such a way that the risk of introducing pathogens into the facilities is minimised. This means that the farm should preferably be sited alone in a unique freshwater system or at a sufficient distance from other farms in sea water, processing plants for aquatic animals, etc. to avoid waterborne spread of infectious agents. Experience in Norway has shown that Aeromonas salmonicida may be disseminated over distances of more than 2 km in sea water, which means that risk of furunculosis spreading from one farm to another is greatly increased if the distance between farms is less than that. Furthermore, epidemiological studies (29) have shown that the risk of contacting infectious salmon anaemia (ISA) from an adjacent farm is twice as high if the distance is less than 5 km. Fish farms in shallow waters may also be at higher risk for disease outbreaks than are fish farms in more open coastal areas. Alternative sites should also be available in order to separate age groups and thus fulfil the ‘All in - all out’ principle. According to Flegel (11) the most important factor for disease prevention in shrimp mariculture is management of the pond environment. In shrimp culture, it is necessary to define the carrying capacity of a single farm and aquaculture area, and then, based on understanding the interactions taking place in a shrimp pond under farming conditions, introduce limitations and regulations by a licensing system. Molluscs are usually cultured in open sea and thus management of the environment will be impossible. Transfers of stocks, mainly in areas where natural recruitment is limited, are the principal source of concern (4). Thirty-eight of the OIE Member Countries (53.5%) responding to the questionnaire reported that they had regulations as regards site selection, while 33 countries had not. b) Water treatment As it is not always possible to obtain an ideal water supply, especially in fresh water, less than perfect solutions must be accepted. Ideally, the water supply to fish hatcheries should be from boreholes, groundwater or surface water with no fish. However, this is often not possible, and pretreatment of water entering the farm may be necessary to improve its quality. This may involve oxygenation of the water, removal of harmful gases dissolved in the water (i.e. nitrogen, hydrogen sulphide, carbon dioxide), temperature control, optimising pH by buffering, reduction of suspended solids, etc. In conventional shrimp culture systems, maintenance of adequate water quality is also essential in order to obtain profitable production. As in fish farming, water quality can be maintained in several ways, such as flushing with clean water, aeration, optimising pH, reduction of organic load, maintaining plankton blooms, etc. (6). As molluscs are sensitive to many anthropogenic pollutants, they require a pristine environment for optimal growth. The technology to obtain optimalisation of these factors is available by means of aeration devices, filtering systems, heat pumps, etc. Disinfection of the water supply as well as the effluent water in land-based farms is also an effective means of disease control. c) Aquatic animal stock In addition to optimal environmental conditions to reduce stress-induced disease factors by optimal localisation of a farm and good water quality, the quality of the aquatic animal population (31) is of great importance in prevention and control of diseases. Management techniques that may be applied include: - 37 -

Conf. OIE 2000

•

Disinfection of eggs prior to introduction into hatcheries

•

Quarantine of fish entering the farm, before they are mixed with existing stock

•

Reduction or elimination of handling or other stress. If aquatic animals (fish, crustaceans) are unavoidably stressed, e.g. during sorting, and/or transportation, they must be given enough time to recover before being subjected to further stress

•

Separation of year classes. ‘All in - all out’ principle. Each population group should ideally be kept separately all the time. However, broad acknowledgement of this principle seems difficult to achieve in modern farming. Less than half of the countries responding to the questionnaire (30 countries [42.2%]) have so far introduced this principle into their aquaculture industry.

•

Optimal density of aquatic animals to avoid crowding stress. It is generally assumed that the density of aquatic animals within a given enclosure is of concern. The response to the questionnaire showed that 24 countries out of 71 had regulations on densities in aquaculture enterprises, which means that at least one-third of the countries are of the opinion that density figures are of important. The density figures will of course have to vary from site to site, depending on the rearing capacity of a certain location and they cannot be standardised.

•

Furthermore any impaired nutritional condition will contribute to reduction in disease resistance at any stage in an aquatic animal’s life. Correct nutritional management is thus also a vital factor for controlling diseases in fish (29). As an example, it is generally accepted that impaired nutritional status may influence mortality in halibut larvae suffering from VNN.

Ideally, the aquatic animals should be derived from a disease-free stock, but that is often impossible to achieve. However, in addition to reduced stress due to optimal environmental conditions, several other factors are of importance. •

Selection of disease-free broodstock. This may be achieved by a continuous disease surveillance programme on the farms (11, 39, 40).

•

Disease control through genetic improvement. Genetic differences in disease resistance in fish have been determined for several diseases both between and within species, but sometimes the problem has been that when a better resistance is achieved against one disease, the same fish show reduced resistance to another disease. A good method for measuring disease resistance is still not fully developed and survival studies are still the only selection criteria used (46). Development of indirect parameters of the immune system as selection criteria, such as lysozym and complement activity, are under way and will be used in the future (36). The development of gene mapping and genetic markers in aquaculture will probably provide tools to eliminate defects and ‘disease’ genes to increase resistance (51). It has been shown in Norway that great differences occur in the survival rates in outbreaks of vibriosis in Atlantic salmon between the offspring of different males.

d) Disease surveillance Major improvements in the health of aquatic animals may be achieved by regular disease surveillance (21, 25). A systematic programme for health control may prevent serious outbreaks of disease, and thus prevent introduction or inadvertent transfer of disease between farms or to wild stocks. An effective health control programme involving regular professional inspection and diagnostic work is of great importance in this respect. Rapid reliable diagnostic work should be carried out by national or provincial laboratories designated for such purposes by the Competent Authority and, if necessary, confirmed by an international reference laboratory for the disease in question. Eighty per cent (57 Member Countries) answered that they had established disease detection at the farm level, which means that appropriate diagnostic service are in place.

- 38 -

Conf. OIE 2000

e) Vaccination Prophylactic control (i.e. vaccination programmes) is one of the most effective preventive measures for controlling serious infectious diseases that cause large economic losses due to fish mortality and increased costs for medical treatment. The term ‘vaccinology’ has been introduced as a scientific term for this field. Correct use of effective vaccines is one of the most important tools in control of infectious diseases in fish, while in shrimps the concept of shrimp immunity remains under discussion. Many products are being sold to shrimp farmers labelled as vaccines or immunostimulants (11). According to Söderhäll and Thörnquist (53) it is difficult or impossible to immunise crustaceans although it is possible to enhance immune capacity for a short time by means of nonspecific immune stimulation (52). As vaccination is useful only in fish farming, the following aspects are based on principles to be considered for fish (18, 35): •

Disease(s) to be vaccinated against

•

Method of vaccination (dip, bath, injection)

•

Vaccination time, single vaccination/re-vaccination/temperature at vaccination.

The disease(s) to be vaccinated against will of course depend on the economically important diseases existing in the country concerned. The vaccination method of choice will depend on fish size, number, etc., and on the price of vaccination per individual fish. Vaccines for fish have to be defined as biological products and should be approved by a Competent Authority of a country. Approval of a vaccine may not mean that it should be approved for general use, as such approval will be dependant on the disease situation and vaccination strategy to be followed in a country as decided by the Competent Authority responsible for disease control in aquatic animals. Of the Member Countries responding to the questionnaire, only 16 (22.5%) countries reported having an ongoing vaccination programme, while 55 countries (77.5%) did not have any policy for vaccination at all. There appears to be a need to increase the awareness of the Competent Authorities responsible for aquatic animal health and to increase their efforts in promoting vaccination of fish in their respective countries. In the Northern Hemisphere, vaccines are only used to control diseases that are widespread in a region or a country, i.e. furunculosis, cold water vibriosis, vibriosis, pasteurellosis, streptococcosis, yersiniosis, etc. Serious viral diseases, such as VHS, IHN, ISA, which have a very limited distribution, should preferably be controlled by other means such as sanitary slaughtering followed by disinfection and fallowing of a site for a certain period. Today, vaccines are commercially available against many of the most important bacterial fish diseases and research is likely to improve the effect of the vaccines. A recombinant vaccine against IPN, a viral disease in several marine fish species, seems to be effective in reducing the disease problems in Atlantic salmon in Norway (7, 14). Currently, intensive research is being undertaken to find effective vaccines against pasteurellosis (38, 49, 55) and streptococcosis (50) in marine fish species. Investigations have also started on vaccination against certain parasitic (58) and viral diseases (57). For fish there is still need for research on: •

Improvement of existing vaccines

•

Improvement of vaccine delivery methods

•

Correct use of vaccines.

Information on correct use and economic benefits from vaccination is also important (32 35). One of the important advantages of vaccination against the widespread bacterial diseases is the reduction in the use of antimicrobials (15, 37). As mollusc do not produce antibodies, vaccination will not be possible in these animals.

- 39 -

Conf. OIE 2000

f) Drugs and chemicals It is widely agreed that medical treatment in a disease prevention and control programme should be regarded as the last choice only. In molluscs raised in open waters, treatment could have a major impact on the environment. Furthermore, the large quantity of antimicrobials required can be a limiting factor as regards possible treatment. In fish farming, however, it may sometimes be essential to carry out medical treatment to control bacterial disease outbreaks for which vaccines are not yet available. A lot of different drugs may be used (2, 23), but in some countries licence regulations restrict them to a very few legally available. The intensive use of drugs in fish farming has potential hazards and side-effects that have been brought to light in recent years. Thus, various legal constraints on the supply and use of veterinary drugs now exist in many countries (1). As can be seen from Figure 2, the use of antibiotics in Norwegian fish farming over the past twenty years has been reduced in spite of an increased production.

450000

45000

400000

40000

350000

35000

300000

30000 250000 25000 200000 20000 150000

15000 10000

100000

5000

50000

Trimeth/sulphadiaz. Oxytetracycline Oxolinic acid Furazolidone Flumequine Florfenicol Production

1998

1997

1996

1995

1994

1993

1992

1991

1990

1989

1988

1987

1986

1985

1984

1983

0 1982

0

Production of salmonids - metric tons

50000

1981

Use of antiobiotics - kilogrammes

Fig. 2 - Use of antibiotics versus salmonid production in Norway

As regards medical treatment in aquaculture, 51 (71.8%) of the responding countries reported that antibiotics and chemotherapeutics had been used. However, as not all countries gave information on the quantity used, it is not possible to give exact figures on the use of drugs. The most common drugs used in the OIE Member Countries are shown in Table 6. In addition, several chemical compounds such as formalin, quarternary ammonium compounds, malachite green, acriflavin, methylene blue, permanganate, sodium hydroxide, etc., have been used both as a prophylactic and as a disease control measure. g) Other control measures on farm level In addition to prophylactic, curative medical treatment of aquatic animals (antibiotics, chemotherapeutics), other important aquaculture operations include collection and destruction of aquatic animals, hygienic and sanitary measures such as disinfection, fallowing, etc. It is of great importance to destroy dead aquatic animals properly at all times and not only during disease outbreaks. If dead aquatic animals are left in the holding facilities (cages, ponds, tanks, etc.), pathogens (e.g. bacteria) may multiply to vast numbers and the infection pressure on the rest of the stock will increase markedly. In periods with recurrent disease outbreaks and high mortality, the proper disposal of fish may pose a problem. Burning, burying, ensilation or delivery to guano production are possible practical alternatives. Ensilation has, however, also certain limitations as it has been shown that IPN virus will survive for more than 6 months in fish ensilage with formic acid at pH 4, while Yersinia ruckeri may survive between 6 and 30 hours. Yersinia ruckeri may also survive, under the same conditions, for more than 12 days in bleeding water/wastewater arising from the on-farm slaughtering process. It is quite unacceptable to leave - 40 -

Conf. OIE 2000

fish lying around on the quay or to throw them into the sea where they will continue to be a source of infection. Thorough examination of aquatic animals to achieve a proper diagnosis is also essential in this respect.

Table 6: Major drugs used in aquaculture in OIE Member Countries Drug

Administration

Indication

Amoxicillin

Oral

Bacterial infections

Ampicillin

Oral

Bacterial infections

Chloramphenicol

Oral/bath/injection

Bacterial infections

Oral/injection

Bacterial kidney disease

Florfenicol

Oral

Bacterial infections

Flumequine

Oral

Bacterial infections

Furazolidone

Oral/bath

Bacterial infections

Nitrofurantoin

Oral

Bacterial infections

Oxolinic acid

Oral

Bacterial infections

Erythromycin

Oxytetracycline, chlortetracycline, tetracycline

Oral/bath/injection

Bacterial infections

Sulphonamides, Potensiated sulphonamides

Oral

Bacterial infections

Terramycin

Oral

Bacterial infections

Benzurones (diflubenzurone, tiflubenzurone)

Oral

Salmon lice

Emacetin

Oral

Salmon lice

Organophosphates, azametiphos

Bath

Salmon lice

Pyretrines (deltametrin, cypermetrin)

Bath

Salmon lice

Praziquantel, metronidazol, phenbendazol, albendazol

Oral

Cestodes

In shrimp it is recognised that imported frozen commodities reprocessed at shrimp packing plants may create a risk of contamination for wild and cultured stocks if wastes (shells, heads, etc.) and wastewater have not been treated adequately or if used for feed for other aquatic animals. Feeding of freshwater crayfish with shrimp infected with white spot disease resulted in a similar disease condition in the crayfish (33, 34). i) Hygienic and sanitary measures Hygienic and sanitary measures are of great importance for preventing and controlling aquatic animal disease. At the farm level, action should include disinfection of tanks, equipment, etc., as well as attention to personal hygiene and working procedures. Disinfection procedures on the farm should include thorough mechanical cleansing, washing by means of high pressure jets, as well as final disinfection using different types of disinfectants. However, the choice of disinfectant must be considered in relation to the material from which the equipment is constructed. Unless a disease is suspected or has been demonstrated, it should not be necessary to disinfect buildings or outdoor areas on the farm. Sanitary working procedures should include the use of different work clothing between infected and noninfected parts of a farm, the latter being attended to first. Disinfection of footwear as well as other personal belongings that may contribute to the spread of diseases, is also necessary. Visitors to an aquaculture establishment should use disposable ‘pull on’ shoes or should disinfect their shoes/boots in an appropriate disinfectant, when both entering and leaving the aquaculture establishment. Also, if the establishment has different sites/areas with different levels of hygienic standards, a foot-bath containing an appropriate disinfectant should be provided at the entrance to each area, and footwear should be disinfected when passing from one area to another. The disinfectant should preferably have an active compound that is not sensitive to the presence of organic material, nor should it decompose rapidly. The ideal compound may be hard to find, but disinfectants based on phenolic compounds, an aldehyde releasing compound or an iodophor are acceptable. The chosen disinfectant must be replaced regularly. Visitors should not come into contact with water where aquatic animals are kept, nor with feed-stuffs or automatic feed dispensers. If samples of water or feed-stuffs are to be collected, they should be taken by the staff. If samples - 41 -

Conf. OIE 2000

have to be taken by the visitors, the visitor should disinfect his/her hands using an appropriate hand disinfectant, or use disposable latex gloves. For these purposes, 70% ethanol, 0.5% chlorhexidine in 70% ethanol, or an iodophor (0.2% iodine) in water or 70% ethanol, or indeed any commercially available hand disinfectant may be used. The staff at the farm should wear clothing and boots/shoes that are used only on the farm. This clothing should be regularly washed in hot water (above 60°C), or disinfected. j) Disinfection of equipment, transport devices, etc. Under normal circumstances, no equipment should leave a farm without thorough disinfection. Small items of technical equipment should be washed using a high-pressure cleaning device to remove all visible contaminants, and should then be disinfected with a suitable disinfectant. The choice of disinfectant should be determined with regard to the material to be disinfected. The wheels of land transport vehicles should be washed using a high-pressure cleaner followed by the application of an appropriate disinfectant. Sea-based transport vehicles (boats) may be difficult to disinfect routinely, but some countries have established routines for disinfection between each transport operation to reduce the risk of spreading disease. However, the crew of the boat should never enter a farm without taking the same precautions as indicated previously for visitors to farms. Equipment that is used at separate sites, tanks or ponds on a farm should be disinfected before each new use. This is easily achieved by placing the equipment in a disinfection bath when not in use and during transport. Again the choice of disinfectant must be considered in relation to the material from which the equipment is constructed. Many OIE Member Countries have developed strict routines for sanitary measures to be taken and 48 Member Countries (67.6%) reported that procedures for disinfection had been established. k) Fallowing In intensive farming it is necessary from time to time to restore (fallow) a site ‘back to normal’, in order to re-establish the natural biological conditions. As it is possible to restock sites all year around, it is more difficult to establish a strict separation between year classes. Fallowing is therefore considered to be an important disease control principle and is of increasing importance, hence fallowing should probably become compulsory, especially in cage culture, not only in connection with disease control and eradication, but also as a standard procedure in general. In some countries this is already a legal requirement but the responses to the questionnaire showed that 47 countries (66.2%) had not implemented fallowing as a ruling principle. The length of the fallow period must be assessed in relation to the survival of a given disease agent when the host is no longer present in the site but also in relation to the number and qualities of the sites (farms) in the combat zone surrounding an affected farm. The fallow period in a disease combat zone should under no circumstances be less than 1 month but a period of at least 6 months would be recommendable. l) Additional responses to the questionnaire In addition to the response from the 71 OIE Member Countries reported above, some questions were directed towards other issues of importance to prevention and control in aquaculture. Research on different aspects of aquatic animal health are important for establishing a sustainable aquaculture industry and 47 Member Countries reported that they had established research programmes in the field, while 24 had not. The opinion of the Member Countries for the future role of the OIE as regards improvements in prevention and control of aquatic animal diseases is also of importance as these opinions will strongly influence the tasks of the OIE Fish Diseases Commission (FDC). Five additional questions were asked covering the following issues:

- 42 -

Conf. OIE 2000

•

Dissemination of more information

•

Conduction of training courses

•

Help with decision-making

•

Advice on specific disease/case problems

•

Others

Sixty-nine Member Countries gave their viewpoints on these topics, while two countries did not. Sixty-three countries were of the opinion that the OIE should disseminate more information to Member Countries. This is an important issue and the FDC will take this question seriously. The FDC will establish its own web page within the OIE’s Web site to bring information to the Member Countries. Sixty-one Member Countries were of the opinion that the OIE should conduct training courses in aquatic animal diagnostic work. The FDC clearly sees the importance of such training courses to establish a quality diagnostic service for aquatic animal diseases in OIE Member Countries. It may, however, be difficult for a small group such as the FDC to carry out such a demanding task, but the FDC will address this question. Forty-eight of the responding Member Countries reported that they would like to have help from the OIE in decision-making on questions of disease prevention and control, and 60 countries wanted to get advice on handling of specific diseases. The FDC will of course be willing to give such advice when asked. As regards the question on other matters that the OIE should consider, several topics were raised. These answers could be summarised as follows: •

Amendments of the list of notifiable diseases

•

Divide Asia into two regions (East and South-East + Middle East and West)

•

Establishment of some reference laboratories in developing countries

•

Harmonisation of disease control measures

•

Help in establishing diagnostic laboratories

•

More attention to the wording of the International Aquatic Animal Health Code

•

Organise meetings, advanced courses, and post-graduate courses in aquatic animal diseases

•

Provide information on risk analysis

•

Reporting on mortality events rather than etiological diagnosis

In addition to this, nineteen of the responding countries commented on issues regarding disease prevention and control that they felt were not covered by the questionnaire. Some of the comments have been dealt with in the questionnaire one way or another, but some were clearly not dealt with. The most important of these issues were as follows: •

Compensation to farmers to facilitate disease reporting

•

Disease-resistant aquatic animals

•

International standardisation of regulations regarding use of drugs and vaccines, and collection of national data on drug use

•

Introduction of quality assurance in aquaculture

•

Private sector involvement in aquaculture and role of insurance underwriters

•

Quality of aquatic animals for restocking purposes in free waters

•

Zoonotic aspect of aquatic animal diseases

As regards compensation to farmers in connection with detection of a notifiable disease, there is no doubt that compensation will increase the farmers willingness to report disease outbreaks. On the other hand, it is my opinion that no Competent Authorities should pay compensation to a private enterprise unless it is - 43 -

Conf. OIE 2000

important to the country to eradicate a disease as soon as possible. Otherwise, in my opinion, the aquaculture enterprises should be covered by private insurance whenever possible. Although the question of genetic improvement of aquatic animals was raised in the questionnaire, selection of disease-resistant aquatic animals and other genetic modifications will be a crucial issue when fish are used for restocking purposes in natural waters. Questions on the use of drugs and vaccines are of importance. Although this has previously been commented on, standardised use of drugs in aquaculture world-wide should be the ultimate goal and all countries should establish a national database of drugs registered for use and the volume used. Even though most diseases of aquatic animals are harmless to human beings, it should be remembered that some pathogens in aquatic animals, such as Mycobacterium marinum, Vibrio vulnificus, Anisakis spp., etc., that may also cause disease in humans and the zoonotic aspect should be considered in the effort to prevent transmission of disease when the principles for prevention and control in aquatic animals are discussed.

3. CONCLUSION AND RECOMMENDATIONS As a summary and conclusion to what has been reported above, it is clearly possible to establish prevention and control measures for aquatic animal diseases. However, in order to achieve this goal, it is necessary to establish a legal framework in order to have the legal basis for any enforcement of disease management measures. When a legal system is in place, it is necessary to address the different aspects of disease prevention and control for aquatic animals. The recommendations for the role of the OIE and its Fish Diseases Commission as regards disease management in aquatic animals would be: •

to continue to develop and refine the OIE International Aquatic Animal Health Code and Diagnostic Manual for Aquatic Animal Diseases to facilitate global applicability

•

to develop a categorisation system for aquatic animal diseases to standardise and facilitate decisions on listing of diseases to be notified on an international basis

•

harmonisation of aquatic animal disease control measures

•

to improve the flow of information on the epidemiological situation world-wide

•

to help in further development of risk analysis methods on aquatic animal health issues

•

to assist the Veterinary Administration and other Competent Authorities on different aspects of aquatic animal health (advice, decision-making, establishing of diagnostic laboratories)

•

to organise scientific/technical meetings and training courses on aquatic animal diseases.

ACKNOWLEDGEMENTS I would like to thank Prof. B. Hill, Dr K. Nakajima, Dr C. Michel, Dr J. Winton, all members of the OIE Fish Diseases Commission, as well as Dr F. Berthe, IFREMER5, for valuable comments, help and support during the preparation of this paper.

5

Institut Français de Recherche pour l’Exploitation de la Mer

- 44 -

Conf. OIE 2000

REFERENCES 1.

Alderman D.J. (1996). Geographical spread of bacterial and fungal diseases in crustaceans. Rev. sci. tech. Off. int. Epiz., 15 (2), 603-632.

2.

Alderman D.J. & Michel C. (1992). Chemotherapy in Aquaculture today. In: Chemotherapy in Aquaculture From theory to reality. Symposium, Paris, France, 12-15 March 1991, ISBN 92-9044-301-4. Alderman D.J. & Michel C., eds. 3-22.

3.

Bartley D. M. & Subasinghe R.P. (1996). Historical aspects of international movements of living aquatic species. Rev. sci. tech. Off. int. Epiz., 15, 387-400.

4.

Berthe F. & Boudry P. (1999). Suivre les huitres et leurs pathogènes à la trace . Biofuture, 195, 38-42.

5.

Broussard M.C. & Warren J.W. (1994). The development of a national aquatic animal health strategy in the United States. International Symposium on Aquatic Animal Health, Program and Abstracts, Seattle, Washington, USA, September 4-8. VI-1.

6.

Chanratchakool P., Turnbull J.F., Funge-Smith S. & Limsuwan C. (1998). Health management in shrimp ponds. Second edition. Aquatic Animal Research Institute, Department of Fisheries, Kasetsart University Campus, Bangkok, Thailand, 111 pp.

7.

Christie K.E. (1997). Immunisation with viral and parasitic antigens: Infectious pancreatic necrosis. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 191-199.

8.

Elston R.E. (1996). International trade in live molluscs: perspectives from Americas. Rev. sci. tech. Off. int. Epiz., 15 (2), 483-490.

9.

European Union (1991). EU Commission Decision 91/42/EEC

10.

European Union (1993). EU Council Directive 93/53/EEC

11.

Flegel T.W. (1998). Shrimp health management and the environment. Report on a Regional Study and Workshop, Aquaculture sustainability and the environment. RETA 5534, Asian Development Bank, Network of Aquaculture Centres in Asia-Pacific (NACA). Annex IV-14, 286-293

12.

Folkestad P. & Torgersen Y. (1999). Disease prevention and control in aquatic animals from a legislative point of view with special reference to Norwegian experiences. Presentation at FAO/NACA/OIE Workshop on Aquatic Animal Diseases, Bangkok, Thailand, 1-5th February, 9 pp.

13.

Food and Agriculture Organization of the United Nations (1996). Aquatic animal quarantine and health certification in Asia. FAO Fisheries Technical Paper, 737, FAO, Roma, Italy, 153 pp.

14.

Frost P., Ness A., Maaseide N.P., Knappskog D.H. & Rødseth O.M. (1997). Efficacy of a recombinant vaccine against infectious pancreatic necrosis in Atlantic salmon post-smolt. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 460.

15.

Grave K., Markestad A. & Bangen M. (1996). Comparison in prescribing patterns of antibacterial drugs in salmonid farming in Norway during the periods 1980-1988 and 1989-1994. J. Vet. Pharmacol. Therapy, 19, 184-191.

16.

Grizel H. (1996). Quelques exemples d’ìntroductions et de transferts de mollusques. Rev. sci. tech. Off. int. Epiz., 15 (2), 401-408.

17.

Grizel H. (1997). Les maladies des mollusques bivalves: Risque et prévention. Rev. sci. tech. Off. int. Epiz., 16 (1), 161-171.

18.

Gudding R., Lillehaug A. & Evensen Ø. (1999). Recent developments in fish vaccinology. Vet. Immunol. Immunopathol., 72, 203-212.

- 45 -

Conf. OIE 2000

19.

Hedrick R. P. (1996). Movements of pathogens with the international trade of live fish: problems and solutions. Rev. sci. tech. Off. int. Epiz., 15 (2), 523-531.

20.

Hill B. J. (1994). European Community measures for control of fish diseases. International Symposium on Aquatic Animal Health, Program and Abstracts, Seattle, Washington, USA, September 4-8. VI- 5.

21.

Hueston W.D. (1993). Assessment of national systems for the surveillance and monitoring of animal health. Rev. sci. tech. Off. int. Epiz., 12 (4), 1187 - 1196.

22.

Håstein T. (1988). Disease control through management practises. Proc. Aquaculture Int. Congr. and Exposition, Vancouver, Canada, September 6-9, 603-606.

23.

Håstein T. (1994). Disease problems, use of drugs, resistance problems and preventive measures in fish farming world-wide. Proceedings of the first International Symposium on Sustainable Fish Farming, Oslo, Norway, Reinertsen H. & Haaland H. eds. A.A. Balkema, Rotterdam, Brookfield, eds. Reinertsen H. & Haaland H., 183194.

24.

Håstein T. (1996). Surveillance and control of marine fish diseases. Report of the 17th Conference of the OIE Regional Commission for Europe, St. Paul`s Bay, Malta. OIE, Paris, France, 19 pp.

25.

Håstein T. (1998). Domestication of animals - The history of domestication of fish. Abstract, 30th International Congress on the History of Veterinary Medicine, Munich, Germany, p. 20.

26.

Håstein T., Hellstrøm A., Jonsson G., Olesen N. J. & Rimaaila-Pärnänen E. (1999). Surveillance of fish diseases in the Nordic countries. NKVet Meeting, Stockholm, Sweden.

27.

Håstein T., Hill B.J. & Winton J.R. (1999). Successful aquatic animal disease emergency programmes. Rev. sci. tech. Off. int. Epiz., 16 (1), 146-160.

28.

International Council for the Exploration of the Sea (1995). ICES Code of Practice on the introductions and transfers of marine organisms. 1994. ICES, 12 pp.

29.

Jarp J. & Karlsen E. (1993). Factors that may reduce the risk of ISA. (In Norwegian).

30.

Kinkelin P.de (1992). The International Office of Epizootics (OIE) and its involvement in aquatic animal health control. Dis. Asian Aquaculture, I, 19-37.

31.

Lall Santosh P. (1988). Disease Control through Nutrition. Proceedings, Aquaculture International Congress and Exposition, Vancouver, British Columbia, Canada, September 6-9, 607-612.

32.

Leira H.L. & Baalsrud K.J. (1997). Operator safety during injection-vaccination of fish. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 383-387.

33.

Lightner D.V. (1996). Epizootiology, distribution and the impact on international trade of two penaeid shrimp viruses in the Americas. Rev. sci. tech. Off. int. Epiz., 15 (2), 579-601.

34.

Lightner D.V., Redman R.M., Poulos B.T., Nunan M.N., Mari J.L. & Hasson K.W. (1997). Risk of spread of penaeid shrimp viruses in the Americas by international movement of live and frozen shrimp. Rev. sci. tech. Off. int. Epiz., 18 (1), 214-227.

35.

Lillehaug A. (1997). Vaccination strategies in seawater cage culture of salmonids. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 401-408.

36.

Lund T., Fjalestad K., Røed K.H. & Strømsheim A. (1992). Use of immune - parametres for indirect selection of increased disease resistance. (In Norwegian). Norsk Fiskeoppdrett, No 11A, 15-16.

37.

Markestad A. & Grave K. (1997). Reduction of antibacterial drug use in Norwegian fish farming due to vaccination. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 365-369.

- 46 -

Conf. OIE 2000

38.

Mazzolini E., Ceschia G., Giorgetti G., Magni A., Passera A. & Danielis L. (1997). Humoral immunity of Sea bass vaccinated intraperitoneally with three preparations of Pasteurella piscicida. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 453.

39.

Mushiake K., Nishizawa T., Nakai T., Furusawa I. and Muroga K. (1994). Control of VNN in Striped Jack: Selection of Spawners Based on the Detection of SJNNV Gene by Polymerase Chain Reaction (PCR). Fish Pathol., 29 (3), 177-182.

40.

Naciri Graven Y., Martin A., Baud J.P., Renault T. & Gerard A. (1998). Selecting the flatoyster Ostrea edulis (L) for survival when infected with the parasite. Bonamia ostrea. J. Exp. Marine Biol. Ecol., 224, 91-107.

41.

Nakajima K. (1999). Prevention and management of diseases in farmed, sea-caught and recreationally caught fish in Asia, the Far East and Oceania. Report of the 21st Conference of the Regional Commission for Asia, the Far East and Oceania, Taipei, Taipei China. OIE, Paris, France, 13-26.

42.

Nash G., Arkarjamon A. & Withyachumnarkul B. (1995). Histological and rapid haemocytic diagnosis of yellowhead diseases in Penaeus monedon (Fabricius). In: Diseases in Asian aquaculture II. Shariff M., Arthur J.R. & Subasinghe R., eds. Fish Health Section, Asian Fisheries Society, Manila, Phillipines, 89-98.

43.

Nickum J. (1994). United States salmonid importation regulations: The philosophy and logic supporting recent revisions. International Symposium on Aquatic Animal Health, Program and Abstracts, Seattle, Sheraton Hotel, Washington, USA, September 4-8. VI- 2.

44.

Office international des épizooties (1997). OIE International Aquatic Animal Health Code and Diagnostic Manual of Aquatic Animal Diseases, second edition. OIE, Paris, France, 192 pp.

45.

Price I.M. & Carey T.G. (1994). International regulations for control of fish diseases - Canadian fish health protection regulations (FHPR). International Symposium on Aquatic Animal Health, Program and Abstracts, Seattle, Sheraton Hotel, Washington, USA, September 4-8. VI-3.

46.

Refstie T. (1988). Disease control through genetics. Proceedings, Aquaculture, International Congress and Exposition. Vancouver, British Columbia, Canada, September 6-9, 613-615.

47.

Renault T. (1996). Appearance and spread of diseases among bivalve molluscs in the northern hemisphere in relation to international trade. Rev. sci. tech. Off. int. Epiz., 15 (2), 551-561.

48.

Roberts R.J. & Muir J.F. (1995). 25 years of world aquaculture: Sustainability, a global problem. In: Sustainable Fish Farming, Reinertsen H & Haaland H., eds., 167-181 .

49.

Romalde J.L. & Magarinos B. (1997). Immunisation with bacterial antigens: Pasteurellosis. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 167-177.

50.

Sakai M. (1997).Efficacy of β-haemolytic streptococcal vaccine in rainbow trout, Oncorhynchus mykiss. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 454.

51.

Slettan, A. (1995). Isolation, characterisation and genetic analysis of simple sequence polymorphism in Atlantic salmon (Salmo salar). Thesis for the degree of Doctor scientiarum. Norwegian College of Veterinary Medicine.

52.

Song Y.L., Liu J.J., Chan L.C. & Sung H.H. (1997). Glucan-induced disease resistance in Tiger shrimp (Penaeus monodon). In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 413-421.

53.

Söderhäll K. & Thörnquist P.O. (1997). Crustacean Immunity - A Short Review. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 45-51.

54.

Tonguthai K. (1985). A preliminary account of ulcerative fish diseases in the Indo-Pacific region (a comprehensive study based on Thai experiences). National Fisheries Institute, Bangkok, Thailand, 39 pp.

55.

Vigneulle M., Gravningen K. & Abiven A. (1997). Vaccination of sea bass (Dicentrarchus labrax) against pasteurellosis and vibriosis: Comparison of different vaccines. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 457. - 47 -

Conf. OIE 2000

56.

Wakabayashi H. (1994). Round table - International regulation for control of fish diseases - Japanese regulations. International Symposium on Aquatic Animal Health, Program and Abstracts, Seattle, Sheraton Hotel, Washington, USA, September 4-8. VI- 4.

57.

Winton J. (1997). Immunisation with viral antigens: Infections haematopoietic necrosis. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 211-220.

58.

Woo P.T.K (1997). Immunisation against parasitic diseases of fish. In: Fish Vaccinology. Gudding R., Lillehaug A., Midtlyng P.J., Brown F., eds. Dev. Biol. Stand., 90, 233-241.

59.

Yoshimizu M. (1996). Disease problems of salmonid fish in Japan caused by international trade. Rev. sci. tech. Off. int. Epiz., 15 (2), 533-549.

- 48 -

Conf. OIE 2000

Appendix 1 List of OIE Member Countries that completed the questionnaire Algeria Angola Argentina Armenia Australia Austria Azerbaijan Belarus Belgium Bosnia and Herzegovina Bulgaria Canada Chad China (People’s Rep. of) Colombia Croatia Cuba Cyprus Czech Rep. Denmark Estonia Finland Germany Ghana

Greece Guatemala Guyana Hungary Iceland India Iran Israel Italy Japan Jordan Korea (Rep. of) Kyrgyzstan Laos Luxembourg Malawi Malaysia Malta Morocco Nepal Netherlands New Caledonia New Zealand Norway

- 49 -

Paraguay Peru Poland Romania Russia Saudi Arabia Senegal Singapore Slovakia Spain Sri Lanka Sudan Sweden Switzerland Syria Taipei China Thailand Turkey Ukraine United Kingdom Vanuatu Vietnam Zimbabwe