Aflatoxins are cancerous secondary metabolites produced primarily by fungus (mould), Aspergillus flavus and Aspergillus parasiticus.
Under favourable conditions typically found in tropical and subtropical regions (high temp (>28°C- <40°C) and high humidity), these moulds can invade food crops, processed foods and feeds, in addition to animal products (eg milk and milk products, eggs and meat from animals fed on contaminated feeds).
Drought stress, insect damage and poor storage conditions also favour mould growth and may lead to higher levels of aflatoxin contamination.
Aflatoxin contamination occurs in major staple crops in East Africa, such as maize, rice and sorghum.
Pre-harvest contamination with aflatoxins is mainly limited to maize, cottonseed, peanuts and tree nuts. Post-harvest contamination can be found in a variety of other crops such as coffee, rice and spices including cinnamon, coriander, and ginger.
High aflatoxin contamination exceeding by far the maximum permissible level of 10 ppb (10 ng/kg) have been reported in maize and ground nuts from Kenya, Tanzania and Uganda.
Short term or long-term exposure to sufficiently high aflatoxin levels can have serious health consequences.
The most vulnerable group of population (relative to adults) is under 2 yr olds (poorly developed detoxication systems). Exposure to aflatoxin during this period leads to wasting, stunting, underweight, frequent infections (due to reduced immunity) and later in life cardiovascular diseases and cancer.
Acute poisoning (short term large ingestion) can be life threatening. Large doses of aflatoxins (1 mg/kg or higher) lead to acute poisoning (aflatoxicosis) characterized by acute liver failure (fever, malaise, anorexia, abdominal pain, nausea, vomiting, jaundice, oedema, bleeding, necrosis of the liver). When consumed over a period of 1–3 weeks, 0.02–0.12 mg/kg bw per day is acutely toxic and potentially lethal.
Low level, chronic exposure to aflatoxins causes cancer affecting all organ systems, especially the liver and kidneys (liver cancer is significantly enhanced in the presence of hepatitis B virus infection); being mutagenic and genotoxic (affects the DNA structure), can potentially cause birth defects in children; children may become stunted in growth; aflatoxins causes immunosuppression, and thus, exacerbates infectious diseases such as hepatitis, human HIV and tuberculosis.
Majority of people in East Africa are not aware of aflatoxin problems and its control strategies. Worse, their socio-economic and food security status of the majority of the inhabitants leaves them few options for choosing low-risk and high quality products.
Therefore, the control of aflatoxin contamination of food and feeds is the most cost-effective way to protect vulnerable members of the population from aflatoxicosis disease.
Preharvest control measures
The most long-term, stable solution to controlling pre-harvest aflatoxin contamination is through enhancing the ability of the crop to resist fungal infection and/or prevent production of aflatoxins by the invading fungus.
This can be achieved through use of resistant varieties, crop rotation, well-timed planting, weed control, pest control especially control of insect pests and avoiding drought and nutritional stress through fertilization and irrigation.
Another strategy for reducing aflatoxins prior to harvest, is a biological control using non-toxigenic A. flavus capable of outcompeting and displacing the mould strains that produce aflatoxins.
Post-harvest interventions that reduce aflatoxin include rapid and proper drying (<9% for peanut kernel, and < 13.5% for corn), proper transportation and packaging, sorting, post-harvest insect control, and the use of approved pesticides as storage protectants.
Other measures include ensuring adequate resources are available for testing and early diagnosis of aflatoxicosis, enforcing strict food safety standards, informing and educating consumers and (small/subsistence) farmers, promoting better livestock feeding and management.
To reduce exposure to aflatoxins, the consumer is advised to:
- Carefully inspect whole grains and nuts for evidence of mould, and discard any that look mouldy, discoloured, or shrivelled.
- Buy grains and nuts as fresh as possible, and which have not been transported over a long time.
- Buy only reputable brands of nuts and nut butters – aflatoxin moulds are not entirely killed by processing or roasting.
- Ensure that foods are stored properly and are not kept for extended periods of time before being used
- Reduce the frequent consumption of ‘high risk’ foods (especially maize and groundnut) and diversifying the diet into less risky staples like sorghum and millet.