Subasinghe, R.P., Bondad-Reantaso, M.G. and McGladdery, S.E. 2001. Aquaculture development, health and wealth. In R.P. Subasinghe, P. Bueno, M.J. Phillips, C. Hough, S.E. McGladdery & J.R. Arthur, eds. Aquaculture in the Third Millennium. Technical Proceedings of the Conference on Aquaculture in the Third Millennium, Bangkok, Thailand, 20-25 February 2000. pp. 167-191. NACA, Bangkok and FAO, Rome.
ABSTRACT: This paper describes how disease has become a primary constraint to sustainable aquaculture production and product trade. It provides specific examples of the impacts of transboundary aquatic animal diseases on international trade, as well as socio-economic and biodiversity implications. Different measures to deal with diseases of fish and shellfish are also enumerated in terms of international codes, regionally oriented guidelines, national programmes and legislation (with specific examples from both developing and developed countries), technology for diagnostics, therapy and information communication. Approaches to aquatic animal health management covering generic (e.g. good husbandry, prevention and control), systems health management and epidemiological approaches and disease surveillance and reporting systems are also discussed.
Aquatic animal health management programmes carried out in different parts of the globe are evaluated with respect to efficacy of disease prophylaxis/control and pathogen detection/disease diagnostics, inherent problems with national legislation and international/regional codes, and the effectiveness of programmes on education, training and extension services. Health management problems that pose risks to rural small-scale aquaculture are discussed, and the need for special consideration of this aquaculture context is emphasized. The need for effective communication at all levels of the production system is also discussed. The roles of the private sector (e.g. aquaculturists, industry associations, cooperatives etc.); professional societies; diagnosticians and researchers; and education, training and other related extension services in effective health management are also discussed. The roles of government at the regional and international levels, along with actions needed to address gaps in effective health management are also discussed.
The importance of aquaculture in meeting increasing demands for aquatic animal
production and its role in providing livelihood opportunities and economic
security are underlined. These and the difficult options available for health
management present a truly big challenge to all concerned. If maintained at
present levels, major epidemics will continue to threaten many sectors, break
out and impact the ultimate goal of aquaculture sustainability.
KEY WORDS: Aquaculture, Health Management, Quarantine, Disease Control, Transboundary Movement
Aquaculture, as clearly indicated elsewhere in these proceedings, is
the fastest growing food-production sector in the world, providing a significant
supplement to, and substitute for, wild aquatic organisms. However, disease
is a primary constraint to the growth of many aquaculture species and
is now responsible for severely impeding both economic and socio-economic
development in many countries of the world. Addressing health questions
with both pro-active and reactive programmes has thus become a primary
requirement for sustaining aquaculture production and product trade.
Diseases notifiable to the OIE means the list of transmissible diseases that are considered to be of socio-economic and/or public health importance within countries and that are significant in the international trade of aquatic animals and aquatic animal products. Reports are normally submitted once a year, although more frequent reporting may be necessary in some cases to comply with Articles 220.127.116.11. and 18.104.22.168. The diseases notifiable to the OIE are set out in Part 2, Section 2.1. and 2.2. of this Code. (Diseases notifiable to the OIE, as used in this Code, were previously known as List B diseases.) (OIE, 2000a).
A brief summary of information on the causative agents of listed diseases, as well as other significant diseases (see definition below), are provided by the OIE (OIE, 2000b), as well as on their website (OIE, 2000c).
Other significant diseases means diseases that are of
current or potential international significance in aquaculture but that
have not been included in the list of diseases notifiable to the OIE because
they are less important than the notifiable diseases; or because their
geographical distribution is limited, or it is too wide for notification
to be meaningful, or it is not yet sufficiently defined; or because the
aetiology of the diseases is not well enough understood; or approved diagnostic
methods are not available. (OIE, 2000a).
|Reports and records of these diseases are provided by an OIE
Collaborating Centre (www.cefas.co.uk/oie.html), in order to keep up-to-date
on their geographic distributions.
In addition to OIE-listed diseases, many more diseases of regional or national interest have significant impacts on aquaculture productivity. Some of these are well-studied and understood, while others are of unknown aetiology or newly emergent. Such diseases can pose equal, if not greater, challenges for aquaculture development in some regions, especially where they fall outside the OIE list and subsequent protection from exposure to unreportable disease agents. For example, Asia has been faced with mass mortalities of cultured marine seabass (Dicentrarchus labrax and Lates spp.) and groupers (Epinephelus spp.) due to several viral diseases. red spot disease has seriously affected grass carp (Ctenopharyngodon idellus) in Vietnam (Phan 2001), and epizootic ulcerative syndrome (EUS) has resulted in mass mortalities of a wide range of wild and cultured species throughout Asia and Australia (Lilley and Roberts, 1997; Lilley et al., 1998). Epizootics in shellfish have also impacted aquaculture in the Asia-Pacific Region, e.g. zhikong scallops (Chlamys farreri) in China (Wei Qi, 2000), Akoya pearl oysters (Pinctada fucata) in Japan (Miyazaki et al., 1999), and related pearl oyster species in Indonesia and the Philippines (Bondad-Reantaso et al., 1999). Microbial diseases also plague crustacean culture, e.g. spawner-isolated mortality virus (SMV) in the shrimp Penaeus monodon and red-claw crayfish, Cherax quadricarinatus (Owens et al., 1998; Owens and McElnea, 2000).
In addition to the direct threat of aquatic pathogens to sympatric wild populations, the confluent nature of the aquatic environment means that use of chemical treatments (disinfectants, therapeutants etc.) in some culture systems may also have untargeted effects. Although chemicals are often used in aquaculture, their use is coming under increased scrutiny and revised disease management practices.
Noninfectious diseases are also common in aquaculture and, although they generally receive less attention than exotic diseases, can have equally devastating effects on production over a very short period. Such diseases are usually caused by various biotic and abiotic conditions.
For example, inadequate management, poor water quality, inappropriate nutrition, aquatic environment degradation (both fresh water and salt water), and exposure to chronic (e.g. urban development pressures as in Manila Bay, Philippines) or acute contamination (e.g. the Erika tanker spill off Brittany, France, in January 2000) have all been linked to mass mortalities of a wide range of cultured and wild species.
Other aquaculture disease implications, frequently overlooked, are those related to zoonoses and other human health and food safety issues. These too are receiving increased attention, not only in relation to human infections, but also with respect to therapeutant residues and, for shellfish, decreasing water quality, toxic algal blooms and faecal coliform bacteria. Although not considered to be a direct threat to the health of the aquatic organism or productivity, there is no doubt about the significant negative impact on marketability, trade and consumer confidence.
Although our capability to manage most of these health issues has grown immensely over the last 20-30 years, the rapid and ongoing development of all aquaculture sectors continues to raise the bar with new health challenges. This is particularly apparent with increased interest in species diversification, as well as new growout techniques. The rapid expansion of these sectors continually surpasses the rate of education, research and adaptation of expertise in health management. Prime examples are mass mortalities of wild abalones off California (Haliotis cracherodii and H. rufescens) and in China (H. discus hannai), sea urchins (Strongylocentrotus droebachiensis) off Nova Scotia and seaweed disease problems in the Philippines, where specialized health expertise is limited to research and assess the potential impact of these on the same species under culture conditions. Furthermore, when a pathogen or microbe causing cytopathic effect (CPE) in a cell-line is detected, its significance, as well as normal distribution in wild or hatchery stocks, is often completely unknown. These gaps in knowledge can cause severe delays in culture development. The actual risks have to be assessed - frequently through controlled and repeated experimental challenges - in addition to extensive field surveys and epidemiological data collection (e.g. husbandry and environmental factors associated with the disease outbreak).
Why is health a constraint to aquaculture?
International trade and health issues
A multitude of factors has contributed to the health problems currently faced by aquaculture. As noted above, over the past three decades aquaculture has expanded, intensified and diversified, based heavily on movements of live aquatic animals and animal products (broodstock, seed and feed). This trend has been triggered by changing circumstances and perspectives, especially world trade liberalization. New outlooks and directions have accelerated the accidental spread and incursion of diseases into new populations and geographic regions, for example, through movements of hatchery-produced stocks and new species for culture, enhancement and development of the ornamental fish trade.
Although translocation of pathogens and diseases with movements of their hosts is by no means a new phenomenon (Hoffman, 1970; Alderman, 1996), it has only recently gained focussed attention in many regions (see Box 1). Advances in live aquatic animal trade, facilitated by improved transportation efficiency, are now recognized as having played a pivotal role in the introduction and spread of pathogens and diseases into many aquaculture systems (see reviews by Hoffman, 1970; ADB/NACA, 1991; Arthur 1995; Hedrick, 1996; Hine, 1996; Renault, 1996; Lightner 1996a; Humphrey et al., 1997; Berthe, 2000; Humphrey, 2001; Subasinghe and Arthur, 2001).
Socio-economic and biodiversity impacts of disease in aquaculture
There is now convincing evidence of the serious socio-economic, environmental and inter-national trade consequences arising from transboundary aquatic animal diseases. These impacts occur on top of the routine needs of managing the opportunistic disease challenges mentioned in the introduction. Bearing this in mind, and taking Asia-Pacific as an example of a region highly dependent upon aquaculture production and capture fisheries, we need to look at exactly what these impacts are.
Precise per annum figures of consequences of disease losses in this area are difficult to pin-down, but some estimates are available, e.g. losses due to EUS in several Asian countries before 1990 exceeded US$10 000 000 (Lilley et al., 1999).
|In Thailand, losses between 1983-1993 were estimated at US$100 million (Chinabut, 1994). Reports of shrimp disease losses range from US$400 milliion in China in 1993 (Wei Qi, 2001), US$17 600 000 in India in 1994 (Subasinghe et al., 1995), US$30 million as early as 1992 in Thailand (Nash et al., 1995) to US$600 million in the same country in 1997 (Chanratchakool et al., 2001). Shrimp losses in Ecuador were estimated at US$280 milllion in 1999 (Alday de Graindorge and Griffith 2001). Marine finfish disease losses in Japan in 1992 were reported at US$114.4 million (Arthur and Ogawa 1996). In Thailand, in 1989, losses due to diseases of cage-cultured seabass and grouper were estimated at US$1.9 million (ADB/NACA, 1991).||In western Europe, annual losses due to viral hemorrhagic
septicaemia virus (VHSV) were estimated at US$60 million (Giorgetti, 1998).
A global estimate of disease losses to aquaculture by the World Bank in
1997 was in the range of US$3 billion per annum.
In addition to the obvious effects of large scale aquaculture losses on rural communities, diseases also cause considerable financial impact on investor confidence. These losses are even more alarming where the success or failure of a harvest will determine the raising of families above or below the United Nations (UN) poverty threshold.
| In southern Vietnam, approximately 1200 families
dependent on rice-shrimp culture have experienced annual losses of >US$300
000 due to shrimp diseases (J.F. Turnbull pers. comm.). Between 1995-1997,
red spot disease of grass carp affected 4000 of 5000 cages in
operation, with losses estimated at US$ 500 000 (RIA 1, 1998). Such losses
directly threaten the livelihoods of the communities they occur in through
reduced food availability and loss of income and employment, as well as
other associated social consequences.
The actual biodiversity impacts of diseases which affect aquaculture are still poorly understood, and may include disease and/or mortalities in the typical host species (expected) both within and outside the culture system, or affect atypical host species (unexpected). Since most diseases thrive best under conditions of easy access to hosts, examples of diseases spreading from culture stocks to surrounding wild populations are rare. However, examples of pathogen detection in wild stocks following a disease outbreak in cultured stocks are beginning to appear. This may simply reflect access to more sensitive pathogen detection tools, i.e. enhanced ability to detect a pathogen in a subclinical carrier. Such detection does not clarify the chicken and the egg question of which came first - the cultured stock infection or the wild stock infection. Obviously, there are ways to pursue this question, however, since most involve circumstantial observations and focus on frequently heated aquaculture-environmental debate, they rarely reach a solid conclusion. The consequences of trickle infections from wild to cultured have predictable consequences, due to the afore-mentioned accessibility of suitable hosts under culture conditions. The consequence of culture-borne transmission to wild stocks is harder to predict. Certainly, there are more examples of infection of cultured stocks via wild stock reservoirs than vice versa (Flegel and Alday-Sanz, 1997; Ruangsri and Supamattaya, 1999; Rajendran et al., 1999; Dixon, 1999).
If an exotic pathogen meets a naïve, but suitable host, regardless
of it being wild or cultured, the effect is usually overt disease, for
example, the spread of Bonamia ostreae throughout naïve populations
of European oysters in The Netherlands (Banning, 1982). Conversely, if
the hosts are not naïve, or have a degree of innate resistance, they
may tolerate the infection and become reservoirs or carriers of the pathogen
in the aquatic system, e.g. Pacific oyster carriage of Haplosporidium
nelsoni, a severe pathogen of Eastern oysters (Crassostrea virginica)
(Burreson, 1996) or WSSV in several wild crustacean reservoirs (Otta et
Some examples of introduced diseases severely impacting biodiversity include crayfish plague (Aphanomyces astaci), which decimated European crayfish populations; the collapse of the shrimp industry in Taiwan Province of China after introduction of monodon baculovirus (MBV), as well as WSSV and YHV introduction to Latin America from Asia (Bartley, 2001).
| These include the OIE International Aquatic
Animal Health Code and Diagnostic Manual for Aquatic Animal Diseases (Hastein,
1996; OIE 2000a, b), the International Council for Exploration of the Sea
(ICES) Code of Practice on the Introductions and Transfers of Marine Organisms
(ICES, 1995); and the European Inland Fisheries Advisory Commission (EIFAC)
Codes of Practice and Manual of Procedures for Consideration of Introductions
and Transfers of Marine and Freshwater Organisms (Turner 1988). Bartley
and Subasinghe (1996) discussed in detail the health provisions in the OIE
and ICES codes. In addition, relevant articles are included in the Food
and Agriculture Organization of the United Nations (FAO) Code of Conduct
for Responsible Fisheries (CCRF) (FAO, 1995), the Convention on Biological
Diversity (CBD, 2000) (http://www.biodiv.org), and the World Trade Organizations
(WTO) Sanitary and Phyto-sanitary (SPS) Agreement (Chillaud, 1996).
Regionally oriented guidelines
Regionally oriented guidelines also exist, e.g. the Great Lakes Fish Disease Control Committee of the Great Lakes Fishery Commission (Meyer et al., 1983) and the North American Commission of the North Atlantic Salmon Conservation Organization (Porter, 1992). The most recent initiative was the Asia Regional Technical Guidelines on Health Management for the Responsible Movement of Live Aquatic Animals and the Beijing Consensus and Implementation Strategy (FAO/NACA, 2000). The Technical Guidelines were based on a set of guiding principles developed through a consultative process that involved representatives from 21 participating governments and technical assistance from regional and international experts on aquatic animal health. The Technical Guidelines describe a number of health management considerations aimed at minimizing the risk of disease spread via aquatic animal movements and were developed to:
| The development of the Technical Guidelines
took into account the different socio-economic and environmental circumstances
of the participating countries in the Asia-Pacific Region, the diversity
of infrastructures (in terms of expertise and institutional capability),
the wide range of aquatic species being moved, the different reasons for
such movements and the diversity of pathogens currently known.
National programmes and legislation
National programmes and legislation are also being implemented in many countries, particularly in developed regions, and these include some good examples of successful fish health control policies and programmes with effective diagnostic accreditation programmes, as well as quality assessment and quality control (QAQC) procedures. These aquatic animal health programmes emphasise good management, adherence to strict hygiene practices and sanitation standards, and general layout of farm premises and site selection, as well as strict quarantine protocols with biosecure facilities. Other successful examples exist under well-defined legislation, including mandatory reporting of disease outbreaks or detection of specific pathogens, as well as recommended mitigative measures and intensive educational and training support.
Australias status of freedom from several major aquatic diseases has given it a comparative advantage, both in terms of production and trade. It has recently launched the AQUAPLAN, which contains Australias five-year national strategic plan for aquatic animal health. AQUAPLAN was prepared through close consultation between government and industry, and describes initiatives ranging from border controls and import certification, through to enhanced veterinary education and capacity to manage incursions of exotic aquatic diseases (AFFA, 1999).
Canada offers another good example of controls such as quarantine, disinfection of eggs, and disease history documentation, which has reduced disease risks associated with the introduction and transfer of Atlantic salmon (Salmo salar). Since 1977, Canada has had federal legislation to protect the countrys fisheries resources, embodied in the Fish Health Protection Regulations (FHPR) and Manual of Compliance (Carey, 1996). Similar regulations are being drafted by Canada for shellfish species (Bower et al., 1994; Bower and McGladdery, 1996).
|Thailand has a good model for establishing strong relationships
between government and industry sectors from a developing country standpoint.
In an effort to maintain its status as the number one shrimp producer in
the Asia-Pacific Region, the government instituted a number of mechanisms
to provide support to the industry. These include re-investing profit from
shrimp exports into improved aquatic animal health capabilities, establishing
a code of conduct for responsible shrimp farming and intensifying support
to shrimp farmers. Thailands Code of Conduct for Marine Shrimp Farming
(CCMSF) was initiated by the government, but developed in collaboration
with the Thai Marine Shrimp Farmers Association, the Thai Frozen Foods
Association, the Thai Food Processors Association and the Aquaculture
Business Club. The CCMSF contains a set of principles and processes that
provide a framework to meet the industrys goals for environmental,
social and economic responsibility (see S. Sen, in this volume). Likewise
in Denmark, the success for controlling VHSV came from strong cooperation
between the countrys veterinary administration and farmers.
Singapore administers an Accredited Ornamental Fish Exporters Scheme where members must observe and comply with the terms and conditions of the programme, as well as a Code of Practice for Accredited Ornamental Fish Exporters. Almost all major exporters are members of this scheme, which emphasises good management, hygiene practices, and general layout of the premise, especially with reference to quarantine facilities (Cheong, 1996). Singapore remains to be the worlds top exporter of live aquatic animals.
Japan has a voluntary system of pathogen inspection carried out by a semi-governmental organization, the Japan Fisheries Resources Conservation Association (JFRCA). This organization provides training to Prefecture government staff and conducts certification of fish health specialists (Gyorui-boheki-shi). The Fisheries Agency has a National Research Institute of Aquaculture with a fish pathology research division, 20 of 47 prefectures have fish disease control centres, as well as a number of universities, all working together for disease control and research (Wakabayashi, 1996).
Diagnostics, therapy and information technology
Diagnostics is determination of the cause of a disease (clinical pathology). The techniques used range from gross observation to highly technical biomolecular-based tools.
Pathogen screening is another health management technique, which focuses on detection of pathogens in subclinical, or apparently healthy, hosts.
Compared to disease diagnosis, screening/surveillance requires detection tools sufficiently sensitive to detect infections in subclinical carriers and/or relatively large sample sizes (OIE, 2000a). Large sample sizes are necessary to provide statistical assurance at set levels of confidence that negative results are acceptable. Positive results are (nearly) always positive. For the most part, screening healthy aquatic organisms for diseases, such as those listed by the OIE, is predominantly a developed-country health management approach, and is directed at international trade protection. However, there is increasing pressure for other countries to adopt this strategy to protect and enhance the international marketability of their aquaculture products. This is becoming more feasible where highly sensitive molecular tools are being developed to detect significant pathogens (e.g. penaeid shrimp viruses).
These tools include both immunoassay and DNA-based diagnostic methods, e.g. fluorescent antibody tests (FAT), enzyme-linked immu-nosorbent assays (ELISA), radio-immunoassay (RIA), in situ hybridization (ISH), dot blot hybridization (DBH) and polymerase chain reaction (PCR) amplification techniques. They are currently used to screen and/or confirm diagnosis of many significant pathogens of cultured finfish (e.g. channel catfish virus (CCV), infectious hematopoeitic necrosis virus (IHNV), infectious pancreatic necrosis virus (IPNV), viral haemorrhagic septicaemia virus (VHSV), viral nervous necrosis virus (VNN) and bacterial kidney disease (BKD)), as well as shrimp diseases (e.g. WSSV, YHV, infectious hypodermic and haematopoeitic necrosis virus (IHHNV) and Taura syndrome virus (TSV)) (Walker and Subasinghe, 2000). Similar tools are under development for molluscan pathogens (Haplosporidium spp., Bonamia ostreae, Marteilia refringens and Herpes virus) (Berthe, 2000). These molecular-based techniques (immunoassays and nucleic-acid assays) provide quick results, with high sensitivity and specificity at relatively low cost, and are particularly valuable for infections which are difficult to detect (e.g. subclinical infections) using standard histology and tissue-culture procedures. Molecular tools are also useful for research into the pathology and immunology of specific infections. They can be used with non lethal sampling and are valuable to monitor challenge experiments under controlled laboratory conditions.
| Further development of this technology is likely
to enhance more rapid detection (field monitoring and laboratory examination)
and diagnosis of disease, which is crucial for early and effective control
of emergent disease situations.
With respect to treatment of disease or pathogen eradication, most countries still rely on chemotherapeutants, especially for the control of infectious microbial diseases of finfish (OIE, 1992). In some production facilities, the prophylactic use of drugs, chemicals and biologicals is necessary to meet the sanitation standards used to maintain high health status/certification. Prophylactic drugs are also used to minimize diseases caused by opportunistic infectious agents and prevent spread via personnel and equipment. Examples include disinfection of hatchery equipment and water supply, antiseptic and antibiotic treatment of surface lesions, and trans-shipment sanitation. Such procedures are particularly useful during handling and transportation (e.g. seining, handling, shipping) when aquatic organisms are most vulnerable to injury, trauma or physiological stress. Chemotherapy has value in preventing and controlling aquatic animal diseases, but must be used in a judicious manner.
Vaccines, developed during the last two to three decades, have also become an established, proven and cost-effective method for controlling certain infectious diseases in cultured animals worldwide. There are now many commercially available for finfish diseases, e.g. enteric red mouth (Yersinia ruckeri), furunculosis (Aeromonas salmonicida), cold water vibriosis or Hitra disease (Vibrio salmoninarum), Vibrio anguillarum serotypes 01 and 02, V. ordalli, Photobacterium (Pasteurella) damsela subsp. piscicida, Streptococcus sp. and IPN and many more are under development (e.g. Flavobacte-rium psychrophilum, Reni-bacterium salmoninarum, IHN, VHS, infectious salmon anaemia (ISA), VNN and Ichthyophthirius multifiliis (Ich). In addition to reducing the severity of disease losses, vaccines also reduce the need for antibiotics, leave no residues in the product or environment and do not induce pathogen resistance. A good example of the results of enhanced vaccine use is the reduction of antibiotic use in Norwegian salmon production (see Fig. 1) (Vinitnantharat, 2001).
| Advances are also being made in both fish and
shellfish immunological research towards stimulation of specific and nonspecific
defence mechanism. See, for example, recent references for specific and
general diseases in Woo and Bruno (1999).
In addition to laboratory and field technology, there has been rapid expansion of computer-based information and training resources (e.g. Internet websites, software, publications and other communication formats) in the last five years. This has lead to a wealth of information, which can be more easily accessed by aquaculture interests in both developed and many developing countries for research, teaching, disease diagnosis and health management (Arthur, 1999). Examples of computerized sources of pertinent information include the FAOs Aquatic Animal Pathogen and Information System (AAPQIS), the OIE Aquatic Animal Disease Information System based at the Centre for Environment, Fisheries and Aquaculture Science (CEFAS), United Kingdom (CEFAS, 2000) and the Department of Fisheries and Oceans (DFO Canada) Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish (Bower and McGladdery, 1996). Addresses for these and other useful websites are provided in Box 2.
What approaches are available for aquatic animal health management?
Generic approach: good husbandry, prevention and control
Active treatment of disease can be problematic, especially for easily stressed aquatic animals or those grown at extremes in their geographic and physiological tolerance range. Other approaches to disease prevention include:
Although disinfection and control of movements can decrease disease spread via personnel, equipment and farmed animals, the infectious agent may still remain in the water system. By the time a diagnosis is confirmed, the agent may have become firmly established, and the fate of most infectious agents in the aquatic environment remains largely unknown. Once an infectious agent is ensconced in a water system, eradication or control of spread becomes more complicated. Preventing the introduction and establishment of a disease agent is, therefore, the preferred health management option. Specific disease situations may demand different approaches and risk management. Cost-benefit analyses may also be required to decide/design the best option (e.g. cull, treat, quarantine, disinfect or fallow). As opportunistic infectious agents abound in most aquatic systems, the best control strategy for these is optimizing husbandry practices, which enhances the aquatic organisms innate ability to suppress progression of an infection into a disease.
For exotic infectious agents, the risk of introduction must be identified, assessed, managed and communicated. Import Risk Analysis (IRA) is a methodical, iterative, science-based process of assessing disease risks associated with the importation of aquatic animals and their products (e.g. genetic material, feed stuff, biological products, pathological material). IRA per se is by no means a new concept, however, the traditional ad hoc and qualitative (gut feeling) approach to the multitude of factors involved with each proposed transfer has come under increasing criticism. Inconsistent decisions and conditions made for different methods of transfer, species and geographic ranges have pushed the demand for a more structured approach to risk analyses for aquatic animal transfers.
| IRA guidelines are now being designed at both the regional/international
and national levels to cover the range of transfer issues which are normally
dealt with under these umbrellas. All, however, have the ultimate goal of
laying down a set of procedures that will enhance consistency of risk analysis,
interpretation of the results and the mitigative (risk-reducing) measures
suggested to redress any risks assessed. Most developed countries
routinely conduct risk assessments for aquatic animal health imports. In
addition, OIE (2000b) provides guidelines on the conduct of IRA for live
The Australian Quarantine and Inspection Service (AQIS) has also published two documents on IRA:
These provide useful information for making IRA and describe the procedures being followed by the Australian government for importing plants, animals and their products.
Systems approach to health management
The aquatic environment is a complex ecosystem which makes the distinction between health, suboptimal performance and disease obscure. During disease outbreaks, the underlying cause is often difficult to ascertain and is usually the end result of a series of linked events involving environmental factors, health condition of the stocks, presence of an infectious agent and/or poor husbandry and management practices. The whole aquatic production environment, including ecological processes, must be taken into consideration. Therefore, an aquatic system health management approach needs to be developed to replace the more traditional pathogen-focused approach applied to disease diagnosis (Subasinghe et al., 1998).
Epidemiology uses the population as the unit of study, where a bidirectional approach (i.e. downward - from population to individual to organ to tissue to cell and to molecule; and upward - from population to farm to district/province to country) provides a more comprehensive and structured insight into understanding a disease process (Thrusfield, 1995) and facilitates development of effective control strategies.
| Although there may be limitations in the use of epidemiological
studies on aquatic animal pathogens, especially those with low or unknown
host-specificity, this approach shows potential for significantly improving
health management and disease control, especially for intensive culture
Disease surveillance and reporting systems
Establishment of national disease surveillance and reporting systems that fulfil regional and international disease reporting obligations are effective strategies for disease control and prevention. They build up an aquatic animal health information base that is useful for verification of disease information generated at the country level, as well as providing a realistic regional picture of the emergence and potential for spread of aquatic diseases. This also serves as a basis for instituting control and eradication programmes plus early warning and emergency preparedness programmes. Surveillance and reporting systems have proven to be effective in terrestrial livestock disease control programmes. In aquatic animal diseases, however, there are various factors that complicate the disease reporting process (Reantaso et al., 2000). Countries with a sound aquatic animal health infrastructure and a demonstrated record of surveillance, containment and control of disease outbreaks have a significant trade advantage over those without such programmes. Surveillance and monitoring systems serve as a value added label to aquaculture and fisheries products because they reflect the countrys commitment and ability to collect and provide documented information on the health, origin and quality of each commodity.
The Network of Aquaculture Centres in Asia-Pacific (NACA), in cooperation
with OIE and FAO, commenced a quarterly aquatic animal disease reporting
system in the Asia-Pacific in 1998 (NACA/FAO, 2000; OIE, 2000d) (Box 3).
This list includes diseases considered to be important with respect to
transboundary movements of aquatic animals in the Asia-Pacific Region.
As a result, an accurate, up-to-date health profile for these diseases
within the region is beginning to emerge.
How effective are health management programmes?
Efficacy of disease prophylaxis and control
While chemotherapy will perhaps remain one of the main strategies for controlling transmissible diseases in the foreseeable future, especially in finfish, there is increasing recognition of its limitations in terms of aquaculture situations, host species and effectiveness against certain pathogen groups. In some cases, rather than providing a solution, chemotherapy may complicate health management by triggering toxicity, resistance, residues and occasionally, public health and environmental consequences (Plumb, 1992; OIE, 1992). In Singapore, for instance, Chong and Chao (1986) reported drug overdoses which led to fish kills and other detrimental side effects. For example, formalin overdose resulted in severe gill damage and ulcerative dermatitis due to repeated treatments. Potassium permanganate use in marine conditions resulted in rapid reduction of (MNO4)- to [MNO2)-, which is toxic to fish. In the 1970s and 1980s, organic tin was used to coat net mesh in Japan to prevent the growth of fouling organisms. This suppressed the propagation of monogenean infections. When the use of the chemical was banned in 1996 because of fear of accumulation in the host fish, as well as adverse environmental concerns, the monogenean infection recurred (Ogawa, 1996).
In addition to side-effects, the efficacy of chemotherapeutants under certain aquatic environments (e.g. open water systems and shellfish beds) is questionable, both with respect to treatment goals and the potential cost of untargeted effects. Occasional misleading claims and advertising regarding the use of antibiotics and other therapeutic drugs have further complicated the use of chemicals for treating health problems. Other problems with effective chemotherapeutant use include (OIE 1992):
|Vaccination is an alternative prophylactic method to control
disease impacts. While some commercial vaccines have proven effective in
providing protection against certain diseases (mainly of finfish), vaccination
is still not possible against shrimp and molluscan pathogens. Their development
requires considerable research on the target disease and involves careful
planning, field trials and cost evaluation.
Efficacy of pathogen detection and disease diagnostics
Disease surveillance and monitoring is an effective and fundamental foundation for any method of disease prevention and control. However, many factors complicate accurate disease reporting.
| These include the wide ranges of socio-economic
and technical development in many countries, diversity of species cultured
(i.e. from invertebrates to reptiles), the range and complexity of environments
used (e.g. freshwater, brackishwater and marine; temperate and tropical
waters), the nature of containment (e.g. ponds, raceways, cages and net-pens),
the intensity of practice (e.g. extensive, semi-intensive, intensive), culture
systems (e.g. monoculture, polyculture and integrated) and management (family
to corporate ownership). The variety of disease issues affecting aquaculture
systems is also highly complicated. Some show little or unknown host specificity
and many elicit non specific clinical signs, e.g. a range of haemorrhagic
bacterial and viral septicaemias. Under these circumstances, there is a
need to identify appropriate techniques for sampling, surveillance and diagnostics,
as well as prioritization of the diseases that should be covered by the
surveillance and reporting systems (Reantaso et al., 2000).
Similarly, current molecular-based diagnostic and pathogen screening techniques have limitations, notably in terms of appropriate applications, standardized sampling, testing procedures and interpretation of results (Walker and Subasinghe, 2000). Because they are leading edge technology, there has been a tendency to use them to replace standard diagnostic techniques without proper evaluation of their effectiveness for specific applications (e.g. screening, diagnosis and epidemiology). Until recently, many have required stringent laboratory conditions for effective use, however, some have now been adapted for field kit use by non specialists. This raises some concerns over interpretation of field diagnosis and proper interpretation of results. This was further discussed with respect to molluscs (Berthe et al., 1999) and is likely to provoke more stringent guidelines for field and laboratory use in the near future (McGladdery, 2000). Such techniques are also of little value for new or emerging diseases where the causative agent is unknown. In these cases, non specific, general techniques - such as histology - are still necessary to accurately interpret pathology and focus in on the potential causative agent(s). This, by necessity, means that sub clinical carriers may escape detection. Thoensen (1994) and Lightner (1996b) list several diseases caused by primary pathogens that lack procedures for detecting sub clinical infections (e.g. coldwater vibriosis or Hitra disease, CCV; Haplosporidium nelsoni (MSX); and H. costale (SSO) of American oysters; and hepatopancreas parvovirus (HPV) of penaeid shrimp.
National legislation and regional/international codes
Even with the best intent, there are some inherent problems with national programmes/legislation and international codes/guidelines. Due to their breadth of scale, they tend to focus on known, significant, diseases and disease agents (listed diseases). In addition, they aim at coverage of the most commonly traded species (i.e. salmonids, catfish, oysters and shrimp). This means that they do not address many diseases of intranational concern, or new and emerging diseases, especially those of local, wild or newly domesticated aquatic organisms that may consequently impact international movements and transfers of live aquatic animals. More comprehensive codes of practice, taking into account health, genetic and ecological impact assessments exist, but are not yet refined or widely applied in many developing countries.
In addition, there are currently few if any codes that give consideration to other possible means of spread of pathogens, such as ballast water from ships. Current ballast water codes and studies tend to concentrate on spread of exotic species and ecological impacts (Johnson and Padilla, 1994; Hayes and Hewitt, 1998; Minchin, 1999). Although the potential for disease transfer is recognized, there is no clear evidence linking ballast to disease introduction to aquaculture sites. Conversely, some aquaculture activities using barge transportation or tank transportation could, unwittingly, be transferring pathogens of the fish or another host with them. Likewise, transfers of mollusc seed in collector bags or lines inevitably include other organisms and such aquaculture substrate has been shown to transfer pest fouling organisms (MacNair and Smith, 1999) so also merit closer scrutiny with respect to disease transfer potential. Techniques to alleviate release of live aquatic organisms, such as ballast water heating (Rigby et al., 1999) do not take pathogens into account. A further problem with control of disease (as well as pest organisms) in ballast water and other hitch-hiking routes is the logistically challenging infrastructure required to implement and enforce codes for dumping, washing etc. In Japan, for instance, even where a strategy is in place and the country has the resources for its implementation, they still face many problems, such as:
Developed countries with well-established strategies and infrastructure, along with stringently enforced complementary regu-lations, still face diseases that have managed to get through the system. Examples include that of bay scallop (Argopecten irradians) introduction to Atlantic Canadian waters, where two protistan parasites were introduced despite rigorous quarantine and inspection (McGladdery et al., 1993). In the United Kingdom, while strict adherence to regulations on salmonid movements prevented the introduction of two salmonid rhabdoviruses, the lack of regulation on ornamental fish resulted in the release of spring viraemia of carp virus (SVCV). France, on the other hand, had a surveillance programme mandated by decree to control IHN, but due to lack of compensation for ordered stock destruction, the surveillance and control measures became essentially ineffective (de Kinkelin and Hedrick, 1991).
Each experience leads to modification of relevant codes and practices, but bearing this in mind, how can countries with fewer resources keep up, let alone comply effectively? Thus, although many developing countries develop and/or enforce national aquatic animal health legislation and regulatory frameworks, these often meet with limited success.
Education, training, and extension services
There has been an increase in the number of diagnostic laboratories,
universities and other institutions offering fish and shellfish health
short- and long-term training courses. However, this number has not matched
the needs of the rapidly developing aquaculture sector, especially in
the developing regions of the world, where most aquaculture activity takes
place. Some education programmes have a strong academic component, but
lack disease diagnosis and/or management experience. Some programmes aim
at specialized disciplines (e.g. bacteriology, immunology, policy-planning
etc.) and, although specialists are important, multidisciplinary approaches
and practical field training are also required.
|A fundamental component of any education or extension service
is effective information communication. For disease information, this is
particularly critical, since misinformation to farmers or consumers can
easily lead to panic, resulting in inappropriate treatments or market closures.
For educational purposes, any disease screening information should include
good pictorial or illustration of procedures, and diseased and normal (healthy)
comparative examples. Many books and other educational media give detailed
text on pathogens and diseases with illustrations of extreme or advanced
cases (e.g. Diagnostic Procedures for Finfish Diseases by Tonguthai et al.
(1999); Australian Aquatic Animal Disease - Identification and Field Guide
by Herfort and Rawlin (1999); EUS Technical Handbook by Lilley et al. (1998);
Handbook of Shrimp Pathology and Diagnostic Procedures for Diseases of Cultured
Penaeid Shrimp (Lightner 1996b). The most significant lack, therefore, is
in the area of early detection - when more subtle clues may be the first
tip off. These should be included in training material, along
with how to follow initial clues to get more accurate and confirmed diagnosis.
Well-illustrated guides for training also span the range of languages and
education levels operating at the farm/site level of the industry - sadly,
such texts and other information media are still rare.
Another fundamental barrier to gaining access to information technology (e.g. computers, software, Internet connection, access to commercial abstracting services), is cost, which may be prohibitive to many researchers and fish health workers from less-developed countries (Arthur, 1999). This is another area that should be borne in mind when designing education and information packages meant to reach remote, rural and underdeveloped regions.
The degree of impact may vary, but a common factor is inadequate knowledge and support for all production systems. For example there is frequently a lack of:
It is necessary to improve the understanding of the risks, impacts, and their avoidance within the context of rural livelihoods. Aquatic animal health management should be included in efforts to integrate aquaculture and enhanced fisheries into overall rural development programmes.
| Such an environment gives strong, healthy juveniles or seed,
optimum growth opportunity and thus, optimum physiological strength to combat
opportunistic health challenges. Other farm-side strategies that can boost
baseline health management are proper nutrition (in the form of appropriate
feeding regimes and proper storage of feed products), good site selection,
proper stocking density, age-class separation and separation of stocks from
different sources. Waste management is another critical area for maintaining
site health. Small decisions, like land disposal of mortalities and waste
materials, control of garbage blowing onto sites etc., can all prevent a
build up of irritant agents which weaken the stock in the face of a health
challenge. Over-riding all these farmside strategies is the need for vigilant
and regular monitoring. Early detection of health problems is the ultimate
key to the best opportunity for control - this is no different from any
other disease situation, including humans! Wherever possible, aquatic animals
showing lesions or aberrant behaviour (including feeding) should be isolated
immediately for investigation. If they are harbouring an infectious agent,
this will reduce its proliferation throughout the system and help reduce
its chances of establishing reservoirs for re-infection.
A critical component of stringent farm-monitoring is consistent and accurate record keeping. Hindsight can be fuzzy when it comes to the first appearance of problems. Feed and growth records are excellent sources of information that can help pinpoint the start of disease problems and, possibly, isolate their source. Depending on the size and type of farm operation (tanks, ponds, open-water cages or lines), record keeping can range from simple (regular monitoring of growth, site or weather conditions) to more detailed recording as outlined in Table 1.
Such records are invaluable for determining the source or nature of a disease outbreak, assisting in accurate and rapid diagnosis, and providing appropriate intervention and control measures.
The private sector (farmers and service providers) should also play an important role in:
Another area where the private sector has a significant role is in working with governments, universities and other institutes to communicate research needs. Where government needs to be open to private-sector input on aquatic animal health control policies and legislation, the private sector should be equally open to government on industry practices which can be modified to improve health and sustainability.
Role of diagnostics and research
The purpose of diagnostics, as previously discussed, is to establish the cause of unfavourable health and recommend effective mitigative measures. When doing disease diagnostic work, the focus should be on the population (and not the individual animal) and production-based indicators of disease, on intervention based on identification, and on prevention rather than treatment. The purpose of research, on the other hand, is to better understand the mechanism of disease processes, in order to provide more effective means of disease management through accurate diagnosis, prevention, control and treatment. In addition, research is often required to establish the cause of emergent disease or confirm the diagnosis of known diseases.
Both research and diagnostics work best when conducted in close association, and both are necessary to ensure that optimal diagnostics and health support for farmers are kept up-to-date and readily available. To achieve this, there should be an improved linkage between farmers, researchers and diagnosticians such that:
There is an urgent need to bridge communication gaps between researchers and farmers in many countries (both developed and developing). This is slowly being achieved through scientist participation in industry workshops, as well as greater industry participation in many scientific fora. Many of the latter include sessions aimed specifically at industry concerns, e.g. the most recent meeting of the National Shellfisheries Association, held in Seattle (March 2000), included a special workshop on green crab invasion of shellfish beds along the Pacific coast. The Asia Pacific Economic Co-operation (APEC) is promoting industry participation in projects also dealing with aquatic animal health.
Recent examples include the APEC FWG 02/2000 Development of a Regional Research Framework on Grouper Virus Transmission and Vaccine Development held in Bangkok, Thailand in October 2000 and APEC FWG 03/2000 Trans-boundary Aquatic Animal Pathogen Transfer and the Development of Harmonised Standards on Aquaculture Health Management - a joint APEC/FAO/NACA/SEMARNAP Expert Consultation held in Puerto Vallarta, Jalisco, Mexico in July 2000, where industry representatives provided valuable interaction with scientists and policy-makers.
One on-going research issue that directly pertains to aquatic animal health is the development of standardized methods for disease diagnosis and pathogen screening, along with regular evaluation of their effectiveness compared with other diagnostic methods. Appropriate application(s) for detection and diagnosis of priority diseases/disease agents also need to be certified (Walker and Subasinghe, 2000).
Considering the wide range of resource expertise and infrastructure required (training, facilities etc.) for disease diagnostics, a phased approach for its establishment and implementation is recommended for countries which currently lack such resources. FAO/NACA (2000) recommends the promotion of three levels of diagnostics according to existing resources (see Table 2). The different levels provide a broad-scale application to disease detection and diagnostics where countries can move from one level to the next as capacities are improved and as resources become available.
The three levels do not exist in isolation but constitute a continuum of activities building on each other, with Level I constituting the essential foundation. The levels are specific to a given disease and not for the entire laboratory capability. Many countries which lack Level I, but have Level II or III capacity, are still highly encouraged to reinforce or establish Level I capability. This is necessary to ensure optimum monitoring feeds into the established diagnostic service/research support infrastructure.
Reference laboratories and collaborating centres of expertise are crucial to the successful implementation of any aquatic animal health programme. Aside from providing generalized support services, confirmatory diagnosis, facilitating research and acting as contact centres for advice and training, they standardize, validate and assist in the quality control of development and research programmes.
Role of professional societies in aquatic animal health management
There are a number of regional and international societies, and in some countries, national societies/networks, that focus mainly on aquatic animal health (e.g. the European Association of Fish Pathologists (EAFP), the Fish Health Section of the Asian Fisheries Society (FHS/AFS), the Fish Health Section of the American Fisheries Society (AFS/FHS), and the Japanese Society of Fish Pathology (JSFP)).
| In addition, subject-specific professional groups and, more
recently, formal associations of farmers, all share a common goal of assisting
in highlighting and researching resolution options for pressing aquatic
animal disease problems. Scientists and researchers have an important role
to play as knowledge producers, while farmers and policy decision-makers
play an essential role in ensuring that the knowledge produced is applicable
and effective for their needs. Involving potential users (e.g. farmers,
particularly via on-farm level trials of research findings) in research
projects at the earliest opportunity is also desirable. Mechanisms by which
scientific findings are integrated into policies on aquatic animal health
need to be identified and reinforced. While industry-science exchange has
improved in many countries over the last ten years, the gap persists between
policy and regulatory planners, licensing authorities and enforcers. A step
in the right direction is the DFO Canada initiative to review all current
legislation pertaining to aquaculture and seek both industry and science
feedback into simplifying the system (cutting out duplication, loopholes,
significant errors and inapplicability) and Australias AQUAPLAN, as
Education, training, extension and related services
There is a need for well-trained personnel in a wide variety of disciplines within the aquatic animal health sector. This is especially apparent for diagnosticians and effective extension biologists in much of the Asia-Pacific and Latin American regions. Diagnosticians who are knowledgeable on a variety of diagnostic techniques, as well as practical field-level health control and disease prevention measures, are particularly needed. Bearing in mind these needs, another fundamental factor affecting the efficacy of education, training and extension services is a global need to bridge the traditional gap between veterinary science expertise and aquatic biology. Both apply to aquatic animal health management and address critical areas without spawning all.
Fundamental paradigms, which need to be reconsidered, include:
Long-term planning for establishing a strong aquatic animal health infrastructure and capacity should be a priority. Unstable health services with discontinuous/transient expertise weaken basic health services. Expertise, by definition, is based on experience. If such experience is fragmented then new recruits lack mentor guidance. Bearing in mind the acute nature of many disease situations, having a stable health support network which is ready to go should be a primary consideration for the aquaculture industry (at the local, national or even international level).
Other areas that may be considered include the following:
Role of national governments
National governments need to show firm commitment to regional/international agreements or policies by implementing stable national aquatic animal health action programmes. They should also establish effective regulations, with the support of enforcement and monitoring policies. Where possible, financial assistance or alternative compensation options for farmers should also be available in the event of production losses or eradication programmes. Furthermore, a functional domestic or national legislation - a major commitment on the part of responsible administration - is a major prerequisite for meeting international trade regulations/guidelines. Governments also need to strengthen the knowledge-base (especially science) upon which policy decisions are made. They should also establish good relationship with industry stakeholders through open communication to determine the most cost-effective solutions to health problems and, once established, such cooperation and trust must be sustained.
An overview of national requirements are:
Role of agencies at regional/ international levels
At the regional/international levels, a regional mechanism for building joint strategies and approaches is required on:
Regional and international agencies play a critical role in supporting regional programmes, setting directions, and providing transparent consultation and information exchange mechanisms that allow other potential cooperators to determine the conditions for their participation. Cooperation must be designed to respond in a cost-effective manner, avoiding duplication of efforts, competition for, and maximized use of limited resources. International assistance to countries seriously affected with aquatic animal diseases is necessary because persistence of uncontrolled/unmonitored disease poses a risk to neighbouring countries and trading partners.
| The varying levels of political, economic and
social development among countries, the transboundary nature and commonality
of many major disease problems, and the need to harmonize approaches all
complicate effective cooperation and consultation. However, all levels of
management and the different sectors involved have to do so in order to
make the most effective use of limited resources - this being one aspect
of global productivity which appears to be sustained below industry requirements.
The current situation offers a big challenge and an opportunity to all concerned
but, if maintained at the present level, major epidemics will continue to
threaten, break out and impact the ultimate goal of aquaculture sustainability.
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1 The views expressed in this manuscript are personal to the authors and do not necessarily reflect the views of FAO, NACA, or DFO Canada.
2 [email protected]
3 [email protected]
4 [email protected]
5 New or first-time diagnoses sholud always be confirmed by retesting or by sending to laboratory specializing in diagnosis of the suspected pathogen.