Introduction

Approximately 40% of the 11 million deaths in children younger than 5 years of age worldwide occur in sub-Saharan Africa (Black et al., 2003). Both child morbidity and mortality are exceptionally high in the region, with 175 deaths per 1000 live births compared to 6 per 1000 in industrialized nations, a 29-fold difference. The major terminal causes of death in these children are diarrhea, pneumonia, malaria, and neonatal disorders (Bryce et al., 2005). These problems are associated with poverty, including insufficient and poor quality food and a high prevalence of malnutrition. Indeed under-nutrition and slowed growth have been identified as an underlying cause of ~50% of the deaths linked to infectious diseases in sub-Saharan African children (Black et al., 2003). Notably, slowed growth and micronu-trient deficiencies are associated with decreased immune and non-immune host defenses that increase susceptibility to the above infectious diseases (Caulfield et al., 2004a,b).

Mycotoxins are metabolites of fungi that contaminate up to 25% of the human food supply. The aflatoxins, including aflatoxins Bj, B2, Gi and G2, are a potent family of myco-

© CAB International 2008. Mycotoxins: Detection Methods, Management, Public Health - 53 -and Agricultural Trade (eds. J. F. Leslie et al.).

toxins produced by Aspergillus spp. that occur on cereals, oilseeds (including peanuts) and tree nuts in parts of the world where the tropical climate facilitates fungal growth. Whilst climatic conditions do not restrict the occurrence of aflatoxin to developing countries, in practice high-technology agricultural practices and the presence and enforcement of government regulatory limits in developed countries translate to exposures that typically are low and sporadic for these latter populations. In contrast, there is little emphasis on agricultural practice to combat aflatoxins in developing countries, and the few regulatory controls are rarely enforced. In addition, it is difficult to envisage such controls being effective when 60-85% of the population are subsistence farmers whose trade often is limited to local markets, where most regulations are unenforceable. Thus, in reality, dietary aflatoxin exposure is a continuous daily problem for the world's poor.

Aflatoxins are potent hepatocarcinogens in animals and epidemiological evidence in human populations, particularly from prospective cohort studies, has led to aflatoxin being classified by the International Agency for Research on Cancer (IARC) as a Class 1 human carcinogen (IARC, 2002). The risk of hepatocellular carcinoma is particularly elevated in individuals with chronic hepatitis B virus infection who also are exposed to aflatoxins (IARC, 2002). Hepatocellular carcinoma is the most common cancer in many parts of sub-Saharan Africa, parts of southeast Asia, and China, with up to 10% of all adult male deaths attributed to this disease.

In addition to hepatocellular carcinoma, aflatoxins are associated with occasional outbreaks of acute aflatoxicosis leading to death shortly after exposure (see Hall and Wild, 1994). In 2004, the consumption of heavily aflatoxin-contaminated maize in Kenya was linked to more than a hundred deaths (Azziz-Baumgartner et al., 2005). In this incident the levels of aflatoxins in maize frequently exceeded 5000 ng/g. Levels > 100 ng/g are common in foods in parts of Africa whilst permitted levels for foods for human consumption in Europe and North America, for example, are generally < 20 ng/g (van Egmond and Jonker, 2004).

Aflatoxin exposure is a result of both the level of contamination in a given commodity and the quantity of the commodity that is consumed. Thus in some areas of the world afla-toxin levels in foods might be relatively high but exposures modest because of a varied diet. However, in sub-Saharan Africa, similar levels of food contamination will translate to a much higher exposure. Dietary staples in the region include two that are highly susceptible to contamination by aflatoxins, namely peanuts and maize. In many countries and regions these staples are consumed daily for the majority of the year and may constitute >50% of the diet. The long-term storage of both crops in hot, humid conditions results in fungal proliferation and increased post-harvest toxin contamination. The result is that aflatoxin exposure in parts of West Africa is ubiquitous and at high levels throughout the life of the people living there (Wild and Turner, 2002).

The problem of aflatoxin contamination must be considered in the context of food sufficiency. Aflatoxin contamination is frequently superimposed on severe problems of food production, storage and availability. For example, one-third to one-half of the people in West Africa live in poverty with a per capita daily energy intake of < 2,500 Kcal (UNEP GEO, 2000). There is marked seasonal variation in food availability, resulting in the so-called "hungry period" where nutrition is inadequate. Consequently, even clearly moldy food may be eaten, as occurred in the recent aflatoxicosis cases in Kenya. This interaction between food safety and food security is crucial when addressing the problem of aflatoxins.

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