FOOD SAFETY MEASURES FOR THE CONTROL OF FOODBORNE TREMATODE INFECTIONS

With over 40 million persons affected throughout the world and more than 10% of the world population being at risk of infection, foodborne trematode infections are a major public health problem. Furthermore some species cause devastating economic losses in livestock. There are indications that these infections have been steadily increasing in recent years. This may be due, among other factors, to increasing production of fish and shellfish especially in traditional, unhygienic fish ponds and to the spread of taste for undercooked or insufficiently processed food. Metacercariae, the infective stage of these parasites, are found in the edible tissues of freshwater fish and shellfish or on edible plants. Our knowledge of their longevity and viability under various conditions of food processing, especially in traditional processing in endemic areas, is rather limited. What little is known indicates that they are more resistant to heating, freezing, salting, etc. than pathogenic bacteria, viruses and some other tissue parasites (Toxoplasma, Cysticerus, etc.). They are, however, highly sensitive to ionizing radiation; most species tested were inactivated by low dose radiation under 1.0 kGy. The basic factor leading to human infection with foodborne trematodes is the ingestion of raw or inadequately processed food: freshwater fish, shellfish and water plants. Moreover, there are sociocultural and environmental factors which augment these infections in aquatic food or favour their transmission to man. A proper understanding of these factors operating locally is essential for planning and application of preventive and control measures. Prevention of contamination of food (fish and shellfish) depends on environmental control of surface waters where fish are caught, hygienic aquaculture and control or elimination of the first intermediate host (snails). These measures may be impracticable in developing countries, especially if large bodies 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 , frying, 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 further study for their ability to inactivate metacercariae in food. Irradiation is a promising and affordable method of inactivating metacercariae in fish and shellfish but it can be applied only where these foods are handled in bulk and the consumers accept them without prejudice. The key to success in the application of the foregoing methods in the control of foodborne trematodiasis is appropriate and effective health education of the public. Food-related behaviour is difficult to change but community involvement based on clear perception of the benefits of control and affordability in social and material terms can facilitate success. Legislation can help in certain aspects of control efforts but cannot replace voluntary compliance induced by health education. Research on epidemiology of these infections in endemic areas and related environmental, sociocultural and boi-ecological studies will reduce costs of and improve chances of success of control programmes.