FOOD SAFETY MEASURES FOR THE CONTROL OF FOODBORNE TREMATODE INFECTIONS

With over 40 million persons affected throughout the world and more th an 10% of the world population being at risk of infection, foodborne t rematode infections are a major public health problem. Furthermore som e species cause devastating economic losses in livestock. There are in dications that these infections have been steadily increasing in recen t years. This may be due, among other factors, to increasing productio n of fish and shellfish especially in traditional, unhygienic fish pon ds and to the spread of taste for undercooked or insufficiently proces sed food. Metacercariae, the infective stage of these parasites, are f ound in the edible tissues of freshwater fish and shellfish or on edib le plants. Our knowledge of their longevity and viability under variou s conditions of food processing, especially in traditional processing in endemic areas, is rather limited. What little is known indicates th at they are more resistant to heating, freezing, salting, etc. than pa thogenic bacteria, viruses and some other tissue parasites (Toxoplasma , Cysticerus, etc.). They are, however, highly sensitive to ionizing r adiation; most species tested were inactivated by low dose radiation u nder 1.0 kGy. The basic factor leading to human infection with foodbor ne trematodes is the ingestion of raw or inadequately processed food: freshwater fish, shellfish and water plants. Moreover, there are socio cultural and environmental factors which augment these infections in a quatic food or favour their transmission to man. A proper understandin g of these factors operating locally is essential for planning and app lication of preventive and control measures. Prevention of contaminati on of food (fish and shellfish) depends on environmental control of su rface waters where fish are caught, hygienic aquaculture and control o r elimination of the first intermediate host (snails). These measures may be impracticable in developing countries, especially if large bodi es of water (rivers, lakes) are involved. It is therefore important to concentrate on preventive and control measures aimed at inactivation of metacercariae in food. The most important method for achieving this is adequate heat treatment, i.e. cooking , roasting, grilling , fryin g, etc. Freezing is another method used for inactivating parasites in food. This method, as well as traditional methods of salting, smoking, fermenting and marinating, widely practised in endemic areas, need fu rther study for their ability to inactivate metacercariae in food. Irr adiation is a promising and affordable method of inactivating metacerc ariae in fish and shellfish but it can be applied only where these foo ds are handled in bulk and the consumers accept them without prejudice . The key to success in the application of the foregoing methods in th e control of foodborne trematodiasis is appropriate and effective heal th education of the public. Food-related behaviour is difficult to cha nge but community involvement based on clear perception of the benefit s of control and affordability in social and material terms can facili tate success. Legislation can help in certain aspects of control effor ts but cannot replace voluntary compliance induced by health education . Research on epidemiology of these infections in endemic areas and re lated environmental, sociocultural and boi-ecological studies will red uce costs of and improve chances of success of control programmes.