Warnings have recently been expressed concerning the hazard posed to wild birds by providing them, with the best of intentions, with aflatoxin-contaminated seeds, peanuts in particular. It is important, from a sound ecological standpoint, to give wild creatures every assistance during the winter months when food is in short supply, but it has been stressed that bird food should be obtained from reputable sources rather than picked up randomly at market stalls where hygiene standards and screening of bulk supplies may be undesirably lax. At the same time, as a commentary in Science for December 24, 1999, points out, aflatoxin poisoning and in particular the liver cancer induced by the toxin, should be viewed in a broader perspective.
It is reported that liver cancer, which is an important public health problem, has an incidence in developing countries of up to 10 times that in their developed neighbours, and that 76 per cent of recorded cases of the disease occur in Asia. The risk factors related to liver cancer include exposure to hepatitis B or C viruses as well as to aflatoxins encountered in foodstuffs. These toxins are metabolites of some species of Aspergillus and are among the most potent hepatocarcinogens known. The most toxic is aflatoxin B1, which has been associated with contaminated peanuts, maize, rice, cottonseed, dried fruits and spices, vegetable oils, cocoa beans and copra. If dairy cattle are fed material contaminated with aflatoxins, a toxic metabolite, aflatoxin M1, may appear in their milk and be a threat to human consumers. Food-borne aflatoxin exposure is common in parts of Africa, China and south-east Asia.
Legal limits for the toxins in finished food products have shown wide variations world-wide, with permissible levels of 4 parts per billion (ppb) in France and the Netherlands to 15-20ppb in Canada and the United States and 30ppb in India. In any country affected, the structure of the traditional diet will determine the real extent of the hazard posed to a population. Moreover, in persons who have been exposed to hepatitis B infection the risk of liver cancer from food contaminated with aflatoxin may be increased to 30-fold.
The Codex Alimentarius drawn up by the World Health Organisation and the US Food and Agriculture Organisation, and adopted by 165 member nations, has prescribed an upper limit of 15ppb of aflatoxin B1 in raw peanuts, and proposes lower limits to apply to milk and dairy products. From the point of view of public health, however, it has been assessed that vaccination against hepatitis B virus would confer a greater advantage than any drastic lowering of aflatoxin limits in efforts to reduce the incidence of liver cancer in developing countries.