The Asia-Pacific Fishery Commission (APFIC)
ad hoc Working Group of Experts in Food Safety held its first meeting at the FAO Regional Office for Asia and the Pacific, Bangkok, Thailand, from15 to 17 March 1999. The establishment of an ad hoc Working Group was agreed by the Twenty-sixth Session of APFIC, held in Beijing, Peoples Republic of China, in September 1998. The recommendation recognized the urgent need for a regional programme of research to address three serious emerging food safety issues associated with sustainable and safe fish production in the region. These issues are:

Trematodes or liver flukes 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 E and SE 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.


1 See related article in FAN No. 19, August 1998, p. 3-7.


David James

Fishery Industries Division


  • human parasicts infestations caused by fish consumption;
  • pathogenic( disease-causing) bacteria associated with fish products;
  • andemerging safety hazards in the products of aquaculture.

In brief, the Working Group aims to encourage the formulation and conduct of a regional integrated research programme and to report progress to the 27th Session of the Commission. It is understood that the programme will require external funding (for which donor support must be found) and will be designed to:

  • quantify current and potential health hazards and risks associated with consumption of fish products; and

  • develop sustainable strategies to mitigate the effects.

Immediately following the Working Group meeting there was a specific workshop on the issue of parasitic infestations caused

by trematodes. The workshop gave the opportunity for a detailed analysis of the problem and the formulation of a proposal for research. rematodes are leaf-shaped flatworms (flukes) that have very complex life cycles, generally involving two intermediate hosts, (snails and freshwater fish). Humans become infected through the ingestion of viable encysted metacercareae of the parasites, which are generally found in the flesh of freshwater fish. 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, Republic of Korea and Viet Nam. The second intermediate hosts are freshwater crayfish and crabs that are often eaten raw, lightly cooked or pickled.

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 United States 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 SE 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.




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. 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 United Kingdom, 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. Polymerase chain reaction (PCR)-based methods have been shown to be useful in detecting the genetic differences between strains.

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. 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. While modern industrial aquaculture, with control over all the inputs, is not implicated as a route of infection there are obvious risks from the uncontrolled use of nightsoil and manure in simple integrated systems.

High value products, such as those for export, are produced under controlled conditions but still the problems of the presence of pathogens and their virulence 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 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.


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 develop-ment, where an individual or institute takes on the responsibility of editing that part of the web site devoted to a specific topic.

Within the area of research into pathogens a planning workshop will be held to develop the following research projects:

  • studies on the serotypes of pathogens in the aquatic environment and development of an understanding of whether they are indigenous to that environment and also possess virulence genes; and

  • studies on antibiotic resistance of bacteria associated with aquaculture systems. Has the development of resistance been correlated with the use of antibiotics to control fish health?

For research into food borne trematode infections, the workshop prepared the following proposals:

  • development of PCR-based methods for the identification of live and dead metacercarea in fish muscle, and

  • epidemiological studies on food borne trematodes and investigation of means of interrupting their life cycles, including their survival in food processing.

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Inland aquaculture research in India; harvesting in stock pond (M.Marzot, FAO)