**1. Introduction**

Africa is faced with the challenge of merging its food crop production with its ever-increas‐ ing population in order to ensure food security of its people. The effort to meet Africa's food demand is however hampered by drought, crop diseases, insect pests, suitable storage facili‐ ties for various agricultural products, markets, lack of fertilizers, flooding, suitable seeds for various agro-ecological zones and poor rural infrastructure. The most limiting aspect and al‐ so ahealth concern is infestation of grains by fungal pathogens that also produce toxic fun‐ gal metabolites called mycotoxins [77, 25]. Though the fungi produce various mycotoxins, aflatoxins are a major concern in Africa [77]. This is partly because of the conducive weather for their accumulation in Africa (wet and humid climates and dry regions), their lethality on ingestion and widespread occurrence in maize (Zea mays) a main stable food crop grown in Africa by small-scale farmers for local consumption [28, 7].What this implies is that the main fungal genera and mycotoxin contaminant of maize in Africa is therefore Aspergillus spe‐ cies and aflatoxins respectively. Aspergillus species and aflatoxins not only attract world‐ wide attention but also are of great significance in Africa due to their negative impact on yield, human health, animal productivity and trade [54, 7, 77, 79, 28]. To exacerbate the problem, Sub Sahara Africa (SSA) experiences high temperatures and high relative humidity that predisposes many crops to fungal pathogens. In addition, majority of farmers in Africa are small scale hence rely on the consumption of homegrown crops. Therefore, irrespective of the quality considerations normally applied by some African governments to control afla‐ toxin contamination in food supply, aflatoxicoses will frequently occur in the continent.

properly cited.

© 2013 Emitati Alakonya and Oranga Monda; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is © 2013 Emitati Alakonya and Oranga Monda; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The high temperatures and high relative humidity predisposes many crops to fungal and other pathogens. There is a significant correlation in aflatoxin levels in products after long storage in Agro-ecological zones with wet and humid climates and dry regions [28]. Maize is a staple food throughout the African continent but is highly colonized by Aspergillus spe‐ cies that produce aflatoxins [7] and the fungal contamination is of great concern. Peanuts (Arachishypogaea) are also grown in many African countries by small-scale farmers for lo‐ cal consumption and also export if food safety regulations are followed. Aflatoxin in pea‐ nuts seeds hamper international trade and also adversely affects health of consumers [54]. There should be reduction in food losses and maintenance of food quality. Due to malnutri‐ tion, there are approximately over 5million deaths in children under the age of 5 years in developing countries every year and aflatoxin contamination is suspected to be a factor in infant under-nutrition [38]. Some of the factors that contribute to aflatoxin contamination in‐ clude; contact of product with soil during drying, high kernel moisture during storage, time of harvest [33]. Aflatoxins are mainly classified in B1 B2 G1 G2 M1 M2 based on chromato‐ graphic and fluorescent characteristics [42]. They occur in maize and other cereal crops, pea‐ nuts, cotton and oil seed crops. When Dairy cattle feed on commodities contaminated with Aflatoxin B1, the toxin is excreted in milk as aflatoxin M1 and can cause DNA damage, gene mutation and chromosomal abnormalities. Aflatoxins particularly B1 is confirmed a poten‐ tial carcinogen [32]. In Kenya Aflatoxin M1 has been reported in milk [37] and in Gambia, Aflatoxin M1 has been detected in breast milk [87]. This leads to maternal exposure of afla‐ toxin M1 in breast milk to young children.

worldwide have aflatoxin induced liver cancer. Of this population 40% occur in Africa [45]. There are economic losses that result from contamination of crops and animal feeds with aflatoxins and also public health problems that result from ingestion of products contami‐ nated with aflatoxins [54, 7]. In many developed countries, there are stringent government regulations on aflatoxins than any other mycotoxins with very low threshold for tolerance [20]. Maximum limit of contamination with aflatoxin in peanuts in Brazil and USA is 20µg/kg while Canada and European Union have imposed a limit of 15µg/kg [24]. For ani‐ mal feeds, European Commission has maximum level for aflatoxins in animal feeds at 0.02mg/kg [21]. A number of African countries still have to put in place regulatory mecha‐ nisms for aflatoxins. However, Kenya's limit for aflatoxin in products for human consump‐ tion is 20ppb [39]. The two general forms of effects of aflatoxins are acute and chronic

A New Approach in Aflatoxin Management in Africa: Targeting Aflatoxin/Sterigmatocystin Biosynthesis in Aspergillus

Species by RNA Silencing Technique http://dx.doi.org/10.5772/51440 43

**a.** Acute toxicity is caused by ingestion of large amount of aflatoxins from heavily conta‐ minated food. This causes decreased liver function and could lead to blood clotting mechanism, jaundice, a decrease in serum proteins that are synthesized by the liver, edema, abdominal pain, vomiting and death of affected person. This was the case in Kenya in 2004 where they were 317 cases and 125 deaths reported due to consumption of maize contaminated with aflatoxins [17, 58] identified the S strain of Aspergillusfla‐ vus as the causal agent of the outbreak. Epidemiological, clinical and experimental studies have indicated that exposure to large doses of aflatoxin causes acute toxicity but exposure to small doses for prolonged periods of time is carcinogenic. The liver is ad‐

versely affected by aflatoxins that cause necrosis of liver cells and death [15].

hepatocellular cancer has been reported in Africa [68].

**3. Management strategies against aflatoxins**

**b.** Chronic toxicity is due to long time exposure to low aflatoxin concentration. The main symptoms are decreased growth rate that leads to stunted growth [26]. In Togo and Be‐ nin, children who are underweight as a result of aflatoxins are also at higher risk for infections and diarrhea [26]. Aflatoxin-albumin adducts (32.8pg/mg) were detected in 99% of children between 9 months – 5 years. Exposure to aflatoxin in children increases at weaning and this contributes to reduced growth [26]. Exposureof children to aflatox‐ in can be through contaminated milk containing Aflatoxin M1 that is a metabolite of AFB1. In domestic animals,aflatoxins cause lowered milk or egg production and im‐ mune suppression that is caused by reactivity of aflatoxin with T-cell and a decrease in vitamin K activities including decrease in phagocytic in macrophages. [61]. It has been reported that there is a high risk among people with Hepatitis B and Hepatitis C carri‐ ers to develop cancer due to consumption of food contaminated with aflatoxins [75]. Aflatoxins have also been linked to immune suppression [70] and higher prevalence of

Aspergillus infection increase with high temperature, high humidity, insect damage and ni‐ trogen deficiency. Temperature and humidity are therefore important in aflatoxin manage‐

toxicity.

The failure of aflatoxin regulatory systems is therefore partly due to existing weather condi‐ tions, poor harvesting, transportation, marketing and processing conditions that favour pro‐ liferation of aflatoxin producing fungi [6, 62, 30, 4, 28, 67]. In addition, the Aspergillusspp have multiple infection courts that include;i) Mycelial growth on the silk kernels and cobs, ii) Kernel wounds created by insects and/or birds, iii) Soil debris and iv) Infected seed which predispose future maize crops to infection which makes it even harder to control [66, 50, 29]. This review summarises the current work on aflatoxins and their management in Africa. Furthermore it presents an argument based on the current knowledge on host and parasite macro and micromoleculartrafficking that suggeststhe possibility to circumvent the aflatox‐ in problem by use of cross species RNA interference. The aim is to arm maize with mole‐ cules that would shut down the aflatoxin biosynthesis upon infection with toxigenic fungi hence thwarting aflatoxin accumulation.

## **2. Health effects associated with aflatoxins**

Aspergillusflavus and Aspergillusparasiticus are of great concern due to production of afla‐ toxins and millions of people in Africa are chronically exposed to aflatoxins due to feeding on contaminated food. The aflatoxin problem is most serious in tropical and subtropical countries due to favorable climatic conditions for Aspergillusflavus and Aspergillusparasiti‐ cus. Human and animals are exposed to aflatoxin through diet [16, 7]. Animal feed is of con‐ cern due to contaminated animal feeds. It is estimated that about 25,200 – 155,000 people worldwide have aflatoxin induced liver cancer. Of this population 40% occur in Africa [45]. There are economic losses that result from contamination of crops and animal feeds with aflatoxins and also public health problems that result from ingestion of products contami‐ nated with aflatoxins [54, 7]. In many developed countries, there are stringent government regulations on aflatoxins than any other mycotoxins with very low threshold for tolerance [20]. Maximum limit of contamination with aflatoxin in peanuts in Brazil and USA is 20µg/kg while Canada and European Union have imposed a limit of 15µg/kg [24]. For ani‐ mal feeds, European Commission has maximum level for aflatoxins in animal feeds at 0.02mg/kg [21]. A number of African countries still have to put in place regulatory mecha‐ nisms for aflatoxins. However, Kenya's limit for aflatoxin in products for human consump‐ tion is 20ppb [39]. The two general forms of effects of aflatoxins are acute and chronic toxicity.

The high temperatures and high relative humidity predisposes many crops to fungal and other pathogens. There is a significant correlation in aflatoxin levels in products after long storage in Agro-ecological zones with wet and humid climates and dry regions [28]. Maize is a staple food throughout the African continent but is highly colonized by Aspergillus spe‐ cies that produce aflatoxins [7] and the fungal contamination is of great concern. Peanuts (Arachishypogaea) are also grown in many African countries by small-scale farmers for lo‐ cal consumption and also export if food safety regulations are followed. Aflatoxin in pea‐ nuts seeds hamper international trade and also adversely affects health of consumers [54]. There should be reduction in food losses and maintenance of food quality. Due to malnutri‐ tion, there are approximately over 5million deaths in children under the age of 5 years in developing countries every year and aflatoxin contamination is suspected to be a factor in infant under-nutrition [38]. Some of the factors that contribute to aflatoxin contamination in‐ clude; contact of product with soil during drying, high kernel moisture during storage, time of harvest [33]. Aflatoxins are mainly classified in B1 B2 G1 G2 M1 M2 based on chromato‐ graphic and fluorescent characteristics [42]. They occur in maize and other cereal crops, pea‐ nuts, cotton and oil seed crops. When Dairy cattle feed on commodities contaminated with Aflatoxin B1, the toxin is excreted in milk as aflatoxin M1 and can cause DNA damage, gene mutation and chromosomal abnormalities. Aflatoxins particularly B1 is confirmed a poten‐ tial carcinogen [32]. In Kenya Aflatoxin M1 has been reported in milk [37] and in Gambia, Aflatoxin M1 has been detected in breast milk [87]. This leads to maternal exposure of afla‐

The failure of aflatoxin regulatory systems is therefore partly due to existing weather condi‐ tions, poor harvesting, transportation, marketing and processing conditions that favour pro‐ liferation of aflatoxin producing fungi [6, 62, 30, 4, 28, 67]. In addition, the Aspergillusspp have multiple infection courts that include;i) Mycelial growth on the silk kernels and cobs, ii) Kernel wounds created by insects and/or birds, iii) Soil debris and iv) Infected seed which predispose future maize crops to infection which makes it even harder to control [66, 50, 29]. This review summarises the current work on aflatoxins and their management in Africa. Furthermore it presents an argument based on the current knowledge on host and parasite macro and micromoleculartrafficking that suggeststhe possibility to circumvent the aflatox‐ in problem by use of cross species RNA interference. The aim is to arm maize with mole‐ cules that would shut down the aflatoxin biosynthesis upon infection with toxigenic fungi

Aspergillusflavus and Aspergillusparasiticus are of great concern due to production of afla‐ toxins and millions of people in Africa are chronically exposed to aflatoxins due to feeding on contaminated food. The aflatoxin problem is most serious in tropical and subtropical countries due to favorable climatic conditions for Aspergillusflavus and Aspergillusparasiti‐ cus. Human and animals are exposed to aflatoxin through diet [16, 7]. Animal feed is of con‐ cern due to contaminated animal feeds. It is estimated that about 25,200 – 155,000 people

toxin M1 in breast milk to young children.

42 Aflatoxins - Recent Advances and Future Prospects

hence thwarting aflatoxin accumulation.

**2. Health effects associated with aflatoxins**

