The Food and Agriculture Organization (FAO) declared that 25% of all crops in the world are affected by aflatoxins. They dominantly affect cereals and millets (maize, sorghum, pearl millet, rice, wheat); oilseeds (groundnut, soybean, rapeseed, sunflower, cotton); spices (chillies, black pepper, coriander, turmeric, ginger); tree nuts (almond, pistachio, walnut, cashewnut, hazelnut, Brazil nut, tiger nut, coconut); pulses (pigeonpea, horse gram, green gram, mung bean, lentil, cowpea, haricot bean); figs, meats, dairy products and fruit juices (apple and guava).
Factors contributing to aflatoxin contamination in groundnut
- Presence of the A. flavus fungus in the soil and air causes infection at every stage from pre-harvest to storage, producing aflatoxin in the kernels.
- Use of susceptible cultivars
- More than 20 days of end-of-season moisture stress to the crop
- Mean soil temperatures of 28-31°C in the pod zone
- Growth cracks and mechanical injury to the pod
- Insect damage to pods by termites or pod borers
- Death caused by diseases (stem, root and pod rots) at pod maturity
- Nematode damage to the pod.
Post-harvest operations include cleaning, grading, transportation, storage, processing, packaging and marketing (Kimatu et al. 2012). The optimal conditions for bulk storage of unshelled groundnuts by farmers for up to one year are 7.5% kernel moisture, a temperature of 100oC and a relative humidity (RH) of 65% (Pattee and Young 1982). Among the post-harvest operations responsible for aflatoxin contamination are:
- Harvesting an overly mature crop, mechanical damage to the pod at harvest
- Stacking the harvest when pod moisture is more than 10% or under high humidity conditions
- Insect damage to the pod during storage
- Storing haulms with immature or small pods
- Presence of gleans in the soil after harvest
- Rewetting stored pods due to factors like ground-moisture or roof
b) Health and regulations
The International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) has classified aflatoxins as Group I (established carcinogens to humans). Aflatoxins cause Aflatoxicosis. The higher prevalence of HCC in Africa is linked to the carcinogenic nature of aflatoxins. Hepatitis B and C carriers are at high risk of developing into hepatocellular cancer on exposure to aflatoxins.
Limited availability of food, environmental conditions favoring fungal development in crops and commodities, and lack of regulatory systems for aflatoxin monitoring and control contribute to acute aflatoxicosis in humans. Studies have shown that ducklings are most susceptible to acute poisoning by aflatoxins. Aflatoxins mainly target the liver. After toxins invade the liver, lipids infiltrate hepatocytes, leading to necrosis or liver cell death. This happens when aflatoxin metabolites react negatively with different cell proteins, inhibiting carbohydrate and lipid metabolism and protein synthesis. Decrease in liver function leads to derangement of the blood clotting mechanism, icterus (jaundice), and a decrease in essential serum proteins synthesized by the liver. Other general signs of aflatoxicosis are edema of the lower extremities, abdominal pain, and vomiting.
HCC due to chronic aflatoxin exposure presents itself most often in those with chronic Hepatitis B virus (HBV) infection (Qian et al. 1994, Groopman et al. 2008), raising the risk of liver cancer up to thirty-fold, compared with exposure alone (Groopman et al. 2008). Both the risk factors are prevalent in poor nations worldwide (Liu and Wu 2010; Wu et al., 2011). Chronic exposure to aflatoxins in animals can inhibit growth and suppress immunity (Khlangwiset et al. 2011). Nursing animals may be affected, and aflatoxin M1 may be excreted in the milk of dairy cattle and other dairy animals. This in turn poses potential health risks to both animals and humans that consume that milk.
Effect on human health
Humans are exposed to aflatoxins by consuming foods contaminated with products of fungal growth. Even though heavily contaminated food supplies are not permitted in the market place in developed countries, concerns remain about the possible adverse effects of long-term exposure to low levels of aflatoxins. Evidence of acute aflatoxicosis in humans has been reported from many countries such as Taiwan, Ouganda, and India with symptoms that include vomiting, abdominal pain, pulmonary edema, convulsions, coma, and death with cerebral edema and fatty involvement of the liver, kidney, and heart.
Expression of aflatoxin-related diseases in humans may be influenced by age, sex, nutritional status, and/or concurrent exposure to other causative agents such as viral hepatitis (HBV) or parasitic infestation. Ingestion of aflatoxin, viral diseases, and hereditary factors have been suggested as possible aetiological agents of childhood cirrhosis. There is evidence that children, malnourished as well, exposed to aflatoxin breast milk, contaminated food and unrefined groundnut oil may develop cirrhosis. Though suggestions have been made that aflatoxin could be an aetiological agent of Reye's syndrome in children in Thailand, New Zealand, etc, there is no conclusive evidence of it. Epidemiological studies have shown the involvement of aflatoxins in Kwashiorkor in malnourished children.
Effects on animals
Aflatoxin lowers resistance to diseases and interferes with vaccine-induced immunity in livestock (Diekman and Green 1992). Suppression of immunity by aflatoxin B1 has been demonstrated in turkeys, chickens, pigs, mice, guinea pigs, and rabbits (Sharma 1993). Swine, ducks, and rainbow trout are very susceptible to it. Broiler chickens are more susceptible to aflatoxin than layer-type chickens. Pale, friable, fatty livers may be evident in acute aflatoxicosis in poultry. Symptoms of acute aflatoxicosis in mammals include inappetance, lethargy, ataxia, rough hair coat, and pale, and enlarged fatty livers. Symptoms of chronic aflatoxin exposure include reduced feed efficiency and milk production, icterus, and decreased appetite (Nibbelink 1986). The mechanism by which aflatoxins reduce growth rate is probably related to disturbances in protein, carbohydrate and lipid metabolism (Cheeke and Shull 1985). Depending on interactions with other factors, aflatoxin concentrations as low as 100 ppb may be toxic to beef cattle, however the toxic level is generally considered to be between 300 to 700 ppb. Garrett et al. (1968) showed an effect on weight gain and intake with diets containing 700 ppb aflatoxin, but not with 300 ppb. Trends in the data suggest that toxicity may occur at the lower concentrations of aflatoxin.
Aflatoxins are inhibitors of nucleic acid synthesis due to their high affinity for nucleic acids and polynucleotides. They decrease protein synthesis, lipid metabolism, and mitochondrial respiration, leading to accumulation of lipids in the liver causing fatty liver. Carcinogenesis has been observed in rats, ducks, mice, trout (most susceptible), and subhuman primates, but rarely seen in poultry or ruminants There is a correlation between aflatoxin presence and increased liver cancer in individuals who are Hepatitis B carriers.
Total maximum aflatoxin levels fixed by different countries for groundnuts/all food products (Codex Alimentarius Commission, 2013).