The aim of preventive and control measures must be to break the life cycle of the parasite. Theoretically, any point of the life cycle can be attacked. In practice the measures must be focused on the following links: (a) elimination of the infection from persons harbouring the parasites; (b) preventing contamination of lakes and rivers with viable tapeworm eggs through appropriate sewage treatment and disposal; and finally (c) preventing transmission of infective larvae from fish to man. As stated earlier, elimination of the parasite from worm carriers is easily achieved today once these are traced. In endemic areas, elimination of the tapeworm eggs from waste waters and sewage systems is an urgent need. If properly dimensioned, modern purification plants eliminate 95-99% of the tapeworm eggs (Bylund et al. 1975) from wastewater. Overloading the plant, however, very rapidly reduces its retention effect and tapeworm eggs passing the plant remain viable. Tapeworm eggs are sensitive to dehydration, low temperatures (< -5°C) and also to chemicals (chlorine, formaldehyde). They are rapidly destroyed in garbage piles and latrines but application of this knowledge is difficult or impossible in communities flushing the faecal products into sewage systems.
It seems obvious that preventive measures should most efficiently focus on preventing the transmission of infective larvae from fish to man. Infected fish must not necessarily be avoided but should be treated in manners rendering the larvae innocuous before the fish is eaten. The plerocercoid do not survive temperatures over +56°C or below -10°C (Pesonen and Wikgren 1960; Salminen 1970). Thus, the infection risk is efficiently eliminated if the fish is fried, boiled, or adequately smoked. The risk is also eliminated and the fish can be eaten even without proper heat treatment (raw, salted, marinated, and hard roe) if the fish is kept in household freeze (-18°C) for a day or two.
Our basic knowledge on all aspects of the life cycle and epidemiology of D. latum is rather complete today. From this knowledge, it is easily emphasized that campaigns aiming at reducing or eliminating diphyllobothriasis from endemic areas should primarily focus on educational work, through public health services, in order to prevent transmission of the infective larvae from fish to man.
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