SUMMARY
Aspergillus flavus is an opportunistic pathogen of crops. It is important because it produces aflatoxin as a secondary metabolite in the seeds of a number of crops both before and after harvest. Aflatoxin is a potent carcinogen that is highly regulated in most countries. In the field, aflatoxin is associated with drought-stressed oilseed crops including maize, peanut, cottonseed and tree nuts. Under the right conditions, the fungus will grow and produce aflatoxin in almost any stored crop seed. In storage, aflatoxin can be controlled by maintaining available moisture at levels below that which will support growth of A. flavus. A number of field control measures are being utilized or explored, including: modification of cultural practices; development of resistant crops through molecular and proteomic techniques; competitive exclusion using strains that do not produce aflatoxin; and development of field treatments that would block aflatoxin production.

Taxonomy: Aspergillus flavus Link (teleomorph unknown) kingdom Fungi, phyllum Ascomycota, order Eurotiales, class Eurotiomycetes, family Trichocomaceae, genus Aspergillus, species flavus.

Host range: Aspergillus flavus has a broad host range as an opportunistic pathogen/saprobe. It is an extremely common soil fungus. The major concern with this fungus in agriculture is that it produces highly carcinogenic toxins called aflatoxins which are a health hazard to animals. In the field, A. flavus is predominantly a problem in the oilseed crops maize, peanuts, cottonseed and tree nuts. Under improper storage conditions, A. flavus is capable of growing and forming aflatoxin in almost any crop seed. It also is a pathogen of animals and insects. In humans it is predominantly an opportunistic pathogen of immunosuppressed patients.

Useful websites: http://www.aspergillusflavus.org, http://www.aflatoxin.info/health.asp, plantpathology.tamu.edu/aflatoxin, http://www.aspergillus.org.uk

Aspergillus flavus: the major producer of aflatoxin

Consecutive outbreaks of acute aflatoxicosis in Kenya in 2004 and 2005 caused > 150 deaths. In response, the Centers for Disease Control and Prevention and the World Health Organization convened a workgroup of international experts and health officials in Geneva, Switzerland, in July 2005. After discussions concerning what is known about aflatoxins, the workgroup identified gaps in current knowledge about acute and chronic human health effects of aflatoxins, surveillance and food monitoring, analytic methods, and the efficacy of intervention strategies. The workgroup also identified public health strategies that could be integrated with current agricultural approaches to resolve gaps in current knowledge and ultimately reduce morbidity and mortality associated with the consumption of aflatoxin-contaminated food in the developing world. Four issues that warrant immediate attention were identified: a) quantify the human health impacts and the burden of disease due to aflatoxin exposure; b) compile an inventory, evaluate the efficacy, and disseminate results of ongoing intervention strategies; c) develop and augment the disease surveillance, food monitoring, laboratory, and public health response capacity of affected regions; and d) develop a response protocol that can be used in the event of an outbreak of acute aflatoxicosis. This report expands on the workgroup's discussions concerning aflatoxin in developing countries and summarizes the findings.

Workgroup Report: Public Health Strategies for Reducing Aflatoxin Exposure in Developing Countries

The Institute of Food Technologists has issued this Scientific Status Summary to update readers on the science of fungal toxins.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1750-3841.2006.00052.x

Food Mycotoxins: An Update

With the increase in regulations regarding the use of antibiotic growth promoters and the rise in consumer demand for poultry products from ‘Raised Without Antibiotics’ or ‘No Antibiotics Ever’ flocks, the quest for alternative products or approaches has intensified in recent years. A great deal of research has focused on the development of antibiotic alternatives to maintain or improve poultry health and performance. This review describes the potential for the various alternatives available to increase animal productivity and help poultry perform to their genetic potential under existing commercial conditions. The classes of alternatives described include probiotics, prebiotics, synbiotics, organic acids, enzymes, phytogenics, antimicrobial peptides, hyperimmune egg antibodies, bacteriophages, clay, and metals. A brief description of the mechanism of action, efficacy, and advantages and disadvantages of their uses are also presented. Though the beneficial effects of many of the alternatives developed have been well demonstrated, the general consensus is that these products lack consistency and the results vary greatly from farm to farm. Furthermore, their mode of action needs to be better defined. Optimal combinations of various alternatives coupled with good management and husbandry practices will be the key to maximize performance and maintain animal productivity, while we move forward with the ultimate goal of reducing antibiotic use in the animal industry.

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Alternatives to antibiotics for maximizing growth performance and feed efficiency in poultry: a review.

Mycotoxins are fungal metabolites commonly occurring in food, which pose a health risk to the consumer. Maximum levels for major mycotoxins allowed in food have been established worldwide. Good agricultural practices, plant disease management, and adequate storage conditions limit mycotoxin levels in the food chain yet do not eliminate mycotoxins completely. Food processing can further reduce mycotoxin levels by physical removal and decontamination by chemical or enzymatic transformation of mycotoxins into less toxic products. Physical removal of mycotoxins is very efficient: manual sorting of grains, nuts, and fruits by farmers as well as automatic sorting by the industry significantly lowers the mean mycotoxin content. Further processing such as milling, steeping, and extrusion can also reduce mycotoxin content. Mycotoxins can be detoxified chemically by reacting with food components and technical aids; these reactions are facilitated by high temperature and alkaline or acidic conditions. Detoxification of mycotoxins can also be achieved enzymatically. Some enzymes able to transform mycotoxins naturally occur in food commodities or are produced during fermentation but more efficient detoxification can be achieved by deliberate introduction of purified enzymes. We recommend integrating evaluation of processing technologies for their impact on mycotoxins into risk management. Processing steps proven to mitigate mycotoxin contamination should be used whenever necessary. Development of detoxification technologies for high-risk commodities should be a priority for research. While physical techniques currently offer the most efficient post-harvest reduction of mycotoxin content in food, biotechnology possesses the largest potential for future developments.

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Impact of food processing and detoxification treatments on mycotoxin contamination.

Safety and efficacy evaluation of aqueous citric acid to degrade B-aflatoxins in maize.

Effect of Sitophilus zeamais and Aspergillus chevalieri on the oxygen level in maize stored hermetically

Decontamination of aflatoxin duckling feed with aqueous citric acid treatment

Hermetic storage system preventing the proliferation of Prostephanus truncatus Horn and storage fungi in maize with different moisture contents

Aspergillus is a fungus that essentially belongs to grains storage flora. It grows optimally at 25 °C with a minimum necessary water activity of 0.75. It starts to produce secondary metabolites at 10-12 oC, but the most toxic ones are produced at 25°C with a water activity of 0.95 (Hesseltine 1976). Those toxic secondary metabolites named aflatoxins (AF) is a group of mycotoxins produced by a large number of Aspergillus species, basically by three phylogenetically distinct sections. The main producers are A. flavus, and A. parasiticus, but it has been demonstrated that A. nomius, A. pseudotamarii, A. parvisclerotigenus, and A.bombycis of section Flavi, A. ochraceoroseus and A. rambellii from section Ochraceorosei and Emericella astellata and E. venezuelensis from Nidulatans section also generate aflatoxins (IARC 2002; Frisvad et. al., 2005). All of them contaminate a large fraction of the world’s food, including maize, rice, sorghum, barley, rye, wheat, peanut, groundnut, soya, cottonseed, and other derivative products made from these primary feedstuffs in low-income countries (Rizzi et al., 2003; Saleemullah et al., 2006; Strosnider et. al., 2006; Masoero et. al., 2007; Caloni, 2010). Although aflatoxins have been a problem throughout history, until 1960 they have been recognized as significant contaminants within agriculture, because in this year they were initially isolated and identified as the causative toxins in “Turkey-X-disease” after 100,000 turkeys died in England from an acute necrosis of the liver and hyperplasia of the bile duct after consuming groundnuts infected with Aspergillus flavus (Asao et. al., 1965; D’Mello, 1997; Strosnider et. al., 2006). Williams et al. estimated in 2004 that 4.5 billion of the world’s population is exposed to aflatoxins because they are also everywhere. Some essential factors that affect aflatoxin contamination include the climate of the region, the genotype of the crop planted, the soil type, the minimum and maximum daily temperatures, and the daily net evaporation (Strosnider et. al., 2006). Moreover, aflatoxin contamination is also promoted by stress or damage to the crop due to drought before harvest, the insect activity, a poor timing of harvest, the heavy rains during and after harvest, and an inadequate drying of the crop before storage. Levels of humidity, temperature, and aeration during storage are also important factors that are

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Ernesto Moreno-Martínez

Papers

Safety and efficacy evaluation of aqueous citric acid to degrade B-aflatoxins in maize.

Effect of Sitophilus zeamais and Aspergillus chevalieri on the oxygen level in maize stored hermetically

Decontamination of aflatoxin duckling feed with aqueous citric acid treatment

Hermetic storage system preventing the proliferation of Prostephanus truncatus Horn and storage fungi in maize with different moisture contents

Aflatoxins and Their Impact on Human and Animal Health: An Emerging Problem