Expert consensus

G. Rees, J. Bartram and D. Kay

1.1 CONTEXT OF THE WORKSHOP

Bivalve shellfish are filter-feeding organisms. They can concentrate microbial pollutants in marine waters including pathogenic species capable of producing disease outbreaks in consuming populations. Control of this disease risk requires integrated management of the water environment used for shellfish growing and harvesting together with post-harvest product processing which might involve depuration and/or heat treatment where appropriate. Perhaps uniquely, therefore, sustainable utilization of this food resource requires continued excellence in the quality of "natural" harvesting waters as well as appropriate management interventions designed to correct any short-term deteriorations in environmental quality. All centres of human population produce the microbial pollutants impacting on shellfish compliance with food quality standards and also contribute the pathogens which can generate disease outbreaks. Sustainable shellfish management, therefore, presents a complex challenge of integrated environmental management encompassing both effluent streams and receiving water quality, together with related food processing and regulation, to achieve end-product quality for consumer protection.

Harvesting shellfish on a global scale is increasing. From a series of regional concentrations, the industry has increased to a total production of 12 million tonnes in 2002, equivalent to 9.4% of the total seafood market, with exports totalling $1.4 billion in 2002. Although, in terms of global trade dollars, this is a relatively small industry, it presents disproportionate health risks because shellfish are often eaten raw or only lightly cooked.

Levels of wild source exploitation for commercial use have remained fairly constant over recent years with the increase in harvested product coming from a growth in aquaculture which comprises 84% of the total bivalve market (2002 figures).

The major global market for shellfish is Asia. The People's Republic of China is responsible for 68% of global production. Import/export of shellfish usually takes place within regional limits. For example, the bulk of live bivalve commerce in Europe is between members of the European Union (EU). China, China (Province of Taiwan), Japan, Malaysia and Thailand are key shellfish trade partners which present the potential for transboundary transport of pathogens.

Food safety is the primary issue in bivalve shellfish trade. The nature of the end product and the associated risks are significant as outlined in chapter 3 of this volume. These are compelling justifications to ensure that bivalve shellfish products are properly tracked through the food chain especially where they cross national borders. Whilst the commercial trade can be regulated relatively easily, there are issues with the "casual" trade which characterizes this product, including its quantification and the undoubted existence of illegal harvesting. The reliability of trade statistics may be sound, but the quantum of casual exploitation is probably impossible to define.

Global experts met at a workshop held in Kuala Lumpur, Malaysia to:

• identify infectious disease risks associated with the consumption of contaminated bivalve shellfish;

• assess water quality management approaches that may reduce the risk of infectious disease; and

• examine and suggest strategies to reduce the risk from pathogens derived from human and/or animal excreta.

The workshop set out to provide guidance to health agencies, water quality and shellfish regulatory agencies and other stakeholders worldwide in recognition of existing and potential future infectious disease problems associated with the consumption of contaminated bivalve shellfish. The efficacy of current practices in protecting human health was assessed and the need for the deployment of new approaches evaluated.

In delimiting the scope of the workshop, initial discussions centred on which shellfish and which contaminants to consider. The workshop elected to maintain an exclusive focus on bivalve shellfish – effectively filter-feeding shellfish predisposed to transmit bacterial and viral pathogens. Throughout this volume, where reference may be made, on occasion, to naturally-occurring pathogens and biotoxins, the reader will be referred to sources of authoritative information.

The workshop also addressed contaminant sources and means of transmission to bivalve shellfish, where possible identifying options to interrupt the cycle. Transmission routes were identified from land- or water-derived contamination (fresh or sea) of harvested products (including harvest for subsistence, recreational, non-market or local sale, or commercial harvest). For the purposes of this publication, post-harvest issues are considered the domain of food safety and post-infection issues the domain of health care and treatment, thus, the focus is specifically on water management aspects and strategies.

1.2 PUBLIC HEALTH FACTORS

Shellfish have been a source of food for thousands of years, as indicated by shellfish middens near ancient human habitation. Human illness caused by infectious agents translated from human or animal sources through shellfish consumption has long been identified.

Minor, self-limiting complaints predominate, although more serious illness may occur...