1. Research funding and coordination
2. Trematodes
3. Pathogens
4. Emerging food safety hazards from aquaculture
5. Research priorities
It is recognized at the outset that any proposals for research that emanate from the Working Group, either for collective or national activities, will require external funding. While the Fish Utilization and Marketing Service of the FAO Fisheries Department is able and willing to take on the role of coordination the available budget is insufficient to cover research activities. Even in regard to coordination some outside assistance will be necessary to improve networking arrangements. As an introduction to this item the Working Group was addressed by Mr Tim Bostock, Executive Secretary of SIFAR, The Support unit for International Fisheries and Aquatic Research (SIFAR) is an independent, donor funded, unit operating from the Fisheries Department of FAO. It was originally set up in Canada as a response to the recommendations of a major Study of International Fisheries Research, and moved to FAO, in Rome, in 1998. The purpose of the unit is to facilitate communication between donors funding fisheries research and the research community at national and regional levels. The objectives are to achieve more relevant research by providing assistance in the formulation of feasible research proposals, better prioritization of research activities and more effective communication. To promote better communication in the fisheries and aquatic research community SIFAR is creating a novel approach through the Internet called "the Onefish Community Directory". The OneFish Community Directory provides the means for stakeholders in fisheries research to collaboratively organise their own information by creating, categorising, and updating knowledge entries in virtually every useful media format. These knowledge workers can each organise a small portion of OneFish and the larger collection of information on fisheries research available on the internet, and present it back to the rest of the population, culling out the bad and useless and keeping only the best content.
The OneFish community-driven approach can harnesses hundreds of human minds to organise information that small paid editorial staffs and ‘search engine robots’ cannot possibly handle and it can also filter out irrelevant information. This initiative could be followed up by any institute in the region prepared to take on the task of acting as the editor for a specific topic.
The Working Group was given an overview of the problems of food borne parasites caused by fish consumption, reserving detailed discussion for the Workshop on that topic (see Appendix 4). Of the three types of food-borne parasites, nematodes, cestodes and trematodes, the latter are of greatest significance where fish consumption is concerned. Nematodes or roundworms transmitted by fish cause some problems in Europe, North America and Japan but are relatively easily killed by cooking or freezing. The species most commonly implicated is Anisakis found in marine fish of temperate origin. Likewise fish-borne cestode (tapeworm) infections are not common in humans, although one species of Diphylobothrium, mainly from cold temperate waters, can be transmitted by freshwater, anadromous and marine fish.
Trematodes or liver flukes, however, are a source of widespread human infection resulting from eating raw or undercooked fish and shellfish. Fish-borne trematode disease is endemic over a large area of the world, including East and Southeast Asia and Russia. WHO indications are that more than 50 million people may be suffering, including more than 10 million each in both China and Thailand. Although the disease is seldom fatal, trematodes can cause serious complications in humans leading to fatalities.
Trematodes are leaf-shaped flatworms (flukes) that have very complex life cycles, generally involving two intermediate hosts, (snails and freshwater fish). Man becomes infected through the ingestion of viable encysted metacercareae of the parasites, which are generally found in the flesh of freshwater fish. The metacercareae can withstand freezing for a period and exposure to elevated temperatures. The life cycle is perpetuated by the constant supply of eggs, shed in human and animal feces, which are taken up by snails. Cercareae released by the snails penetrate the gills and under the scales of fish and encyst in the muscle as metacercareae. The life cycle can be interrupted by not allowing sewage contamination of water bodies and not using nightsoil as fertilizer in aquaculture. Alternatively consumers should avoid eating raw freshwater fish and ensure that what is eaten is properly cooked. While these measures may appear to offer simple solutions it has proved difficult to change ingrained food habits and there is a tendency to rely on controlling the problem with the effective drugs that are available. However, the cost of these drugs puts them beyond the reach of poor consumers. The role of HACCP in controlling the disease was discussed. While this may be possible in the production phase of industrialised aquaculture it would be difficult, if not impossible in integrated aquaculture systems and in the wild. Control of the disease requires more research on the epidemiology of infection, better means of identification of infested fish and better diagnostic methods.
Of the trematode liver flukes, Clonorchis sinesis is endemic in China, Japan, Korea and Vietnam, while Opisthorchis viverrini infests Southeast Asia and Opisthorchis felineus is found in Russia. The flukes attach to the bile ducts and cause damage, gastro-intestinal problems, jaundice and fatigue. There is also an associated increase in liver cancers. Cyprinids, the major source of freshwater fish both from capture fisheries and aquaculture, are very commonly implicated as the intermediate fish host. Lung flukes caused by a number of Paragonimus species are found in China, Korea and Vietnam. The second intermediate hosts are freshwater crayfish and crabs that are often eaten raw, lightly cooked or pickled.
The Report of the Workshop (Appendix 4) suggests a work programme for a regional research effort to combat the debilitating effects of the disease and the associated high cost in both social and economic terms.
Although fish products are not implicated as a major cause of food poisoning outbreaks there is a disturbing trend of increasing incidences of reported cases of food borne illness throughout the world. It is not yet clear whether this is due to better reporting, globalization of trade or an increase in virulence of the causative organisms. Action is required in the region in order to protect valuable export markets as well as the health of consumers.
Despite the low incidence of food poisoning caused by fish, the safety of fish products carrying bacteria and viruses that are recognized as human pathogens is often questioned. A wide range of organisms has come under suspicion as a result of their isolation by the regulatory authorities of the countries that provide the largest markets for fish products. The list of organisms includes: Vibrio cholerae, V. parahaemolyticus, V. vulnificus, Salmonella, Shigella, Listeria monocytogenes, pathogenic varieties of Escherichia coli, etc. While the isolation of these organisms in importing countries is considered to be a result of unhygenic handling and processing, some of them may be indigenous in the tropical aquatic environment from which the product came. It is well known that only relatively few strains of many potential pathogens are in fact virulent. To ensure food safety it is important to understand which of the organisms are indigenous and which are contaminants. For example there is a lot of scientific evidence to indicate that V. cholerae makes up part of the normal flora of the aquatic environment and can be detected even from waters that are not fecally contaminated. This has been demonstrated in the eastern United States and in the UK, in addition to tropical areas. Only two cholera serotypes (V. cholerea 01 and 0139) have been shown to cause the disease and these strains, which produce cholera toxin, are genetically different.
Similarly V. parahaemolyticus is part of the flora of the coastal and brackish water environment but only 1 percent of the bacterial population is virulent. Determination of the hazards posed by these organisms requires the detection of toxigenic strains. Polymerase chain reaction (PCR)-based methods have been shown to be useful in detecting the genetic differences between strains.
Salmonella has previously been of greatest concern, particularly to the USFDA which has consistently maintained a zero tolerance for the organism, claiming that its presence is always the result of fecal contamination as salmonella is not indigenous to the aquatic environment. However, there is increasing evidence that, even in catfish ponds in the USA and eel ponds in Japan, salmonella is naturally present in the environment. The presence of salmonella has previously been convincingly demonstrated in shrimp culture ponds in Southeast Asia and the coastal environment in India. However, most of these indigenous aquatic strains belong to the serotype S weltevreden, which is not commonly associated with human infections. As further evidence to support the case for removal of the zero tolerance it would be useful to determine whether such aquatic strains possess the potential to cause disease in humans. PCR-based techniques would be helpful in such studies.
While L. monocytogenes is a considerable problem in temperate areas it has been implicated very seldom as a causative agent of disease in the tropics. It would be important to establish whether those few serotypes involved in human infections are found in tropical fish products or the processing environment. More information is also required for E. coli. Although pathogenic strains are considered dangerous the role of fish in the transmission of disease has yet to be established.
Although products from marine capture fisheries in the region have a generally good history of safety there are concerns that with increasing intensification of aquaculture new problems may arise. Asia accounts for the overwhelming proportion (over 90 percent) of world aquaculture production and there are some projections that half of the food fish supply will be produced by culture early in the next century. Assurance of the safety and quality of the products is therefore vital.
Potential problems in the domestic markets could occur through trematode infestation, sustained by the use of human and animal wastes for fertilization and the continuation of traditional food habits. These problems have been reviewed above for the production sector as a whole but they are of particular relevance to the rapidly expanding aquaculture industry.
High value products, such as those for export, are produced under much more controlled conditions but still the problems of the presence of pathogens and their virulence, as outlined above, need to be addressed. Of particular concern is the emergence in recent years of a pattern of resistance to antibiotics by disease causing organisms. Although there is little direct proof, in the minds of many, the increasing frequency of resistance has been associated with the excessive use of antibiotics in intensive aquaculture systems. In the past they were used prophylactically in the feed and, although today use has decreased, large quantities are still employed for the purposes of controlling fish health. The resistance can easily be transferred both to fish pathogens and human pathogens, causing eventual difficulties in chemotherapy. Although it has yet to be established whether the emergence of antibiotic resistance is due to aquaculture practices (there is also widespread misuse of antibiotics in the medical and veterinary fields) the extent of the responsibility of aquaculture needs to be studied.
As the study of pathogens and the need to combat emerging problems in aquaculture have many common points it was decided to consider them together and to arrange a planning workshop at a later date. This workshop would formulate research proposals for a regional research programme. Such a programme would include the conduct of a series of studies to protect the health of consumers, and to collect and present evidence to the regulatory authorities in importing countries that their standards should be modified to take into account the actualities of the tropical environment.
The first requirement was recognized as a need for better communication at regional and international levels. There are opportunities to achieve this by making use of the SIFAR OneFish Community Directory, currently under development. It was agreed that the Fisheries College, Mangalore, India and the Technical Secretary of the Working Group would discuss how this could be arranged, with the Fisheries College acting as the editor for this sector through the Internet connection.
Specific research projects to be elaborated at the workshop would include:
The possibilities of holding the workshop in Mangalore, India, in December 1999 will be kept under review by the Technical Secretary, but will be subject to the availability of FAO funds.
*****
