Mycotoxins In Agricultural Commodities: A Global Threat

The term mycotoxin was coined in 1962 in the aftermath of an unusual veterinary crisis near London, England, during which approximately 100,000 turkey poults died. This mysterious turkey X disease was linked to a peanut (groundnut) meal contaminated with secondary metabolites from Aspergillus flavus (aflatoxins). These toxic chemical compounds-mycotoxins are a serious food safety threat as they cause disease and death in humans and animals worldwide.

Currently, more than 300 mycotoxins are known, scientific attention is focused mainly on those that have proven to be carcinogenic and/or toxic. Human exposure to mycotoxins may result from consumption of plant-derived foods that are contaminated with toxins, the carry-over of mycotoxins and their metabolites in animal products such as meat and eggs or exposure to air and dust containing toxins. Examples of mycotoxins of greatest public health and agro-economic significance include aflatoxins (AF), ochratoxins (OT), trichothecenes, zearalenone (ZEN), fumonisins (F), tremorgenic toxins, and ergot alkaloids. These toxins account for millions of dollars annually in losses worldwide in human health, animal health, and condemned agricultural products.

Occurrence and significance of mycotoxins in foods and feeds:

Mycotoxicoses in humans or animals are characterized as food or feed related, non-contagious, non-transferable, non-infectious, and non-traceable to microorganisms other than fungi. Clinical symptoms usually subside upon removal of contaminated food or feed. A wide range of commodities can be contaminated with mycotoxins both pre- and post-harvest.

Aflatoxins derived fromAspergillus flavus is a common contaminant in agriculture.Aflatoxins (AFTs) are found in maize, dried fruits and peanuts. Aflatoxin is associated with both toxicity and carcinogenicity in human and animal populations. Acute aflatoxicosis results in death; chronic aflatoxicosis results in cancer and immune suppression..

Ochratoxin A (OTA) is a secondary metabolite produced by several species of Aspergillus and Penicillium. The toxin, which is a nephrotoxic and nephrocarcinogenic compound, has mainly been found in cereals as well as poultry meat and kidneys. It occurs in the kidney, liver and blood of farm animals by transfer from animal feed.

Zearalenone produced by various species of Fusarium, in particular Fusarium graminearum and Fusarium culmorum, and is significantly toxic to the reproductive system of animals.

Fumonisins (B1 and B2) are cancer-promoting metabolites of Fusarium proliferatum and Fusarium verticillioides. Fumonisin B1 (FB1) is the most toxic and has been shown to promote human oesophageal cancer in various parts of Africa, Central America, and Asia.

The trichothecene mycotoxins (TCT) comprise a vast group of over 100 fungal metabolites occur worldwide in corn, wheat, barley, oats, rice, rye, vegetables, and other crops. Natural occurrence of TCT has been reported in Asia, Africa, South America, Europe, and North America. They are common contaminants of poultry feeds and feedstuffs and their adverse effects on poultry health and productivity.

Moniliformin is produced by several Fusarium species (mainly F. proliferatum) and is usually found on the corn kernel. It can be transferred to next generation crops and survive for years in the soil.

Mycotoxins in key commodities in Bangladesh

Of the foods and feeds tested, the incidence of aflatoxin contamination varied from low (rice collected from farmers’ stores, 8%) to high (maize, 67%). Both the average total aflatoxin contents (< 1.0 microg/kg) and the maximum aflatoxin B1 contents (< or = 5.0 microg/kg) recorded for pulses, rice and its various products, and wheat were low. The levels of contamination of maize, roasted and raw groundnuts, and poultry feed were considerably higher, with average total aflatoxin B1 contents of 33, 13, 65, and 7 microg/kg, respectively, and maximum aflatoxin B1 contents of 245, 79, 480, and 160 microg/kg, respectively. Fumonisin B1, ochratoxin A, zearalenone, deoxynivalenol, and T-2 toxin were found, to any significant extent, only in some of the maize samples tested, always accompanied by aflatoxins. One sample of maize contained five mycotoxins, namely, the aflatoxins, fumonisin B1, deoxynivalenol, zearalenone, and ochratoxin A.

Factors affecting production, contamination of foods and feeds, and toxicity of mycotoxins

A main difficulty in assessing the risk of mycotoxins to human and animal health is the multiplicity of factors affecting the production or presence of mycotoxins in foods or feeds. Scientists categorized the factors as physical, chemical, and biological.

Physical factors include the environmental conditions conducive to fungal colonization and mycotoxin production such as temperature, relative humidity, and insect infestation. Chemical factors include the use of fungicides and/or fertilizers. Stresses such as drought, an increase in temperature, and an increase in relative humidity may selectively alter colonization and metabolism of mycotoxigenic fungi and thus alter mycotoxin production. The biological factors are based on the interactions between the colonizing toxigenic fungal species and substrate. While some plant species are more susceptible to colonization, environmental conditions may increase the vulnerability of other more resistant plant species.

Economic impact of mycotoxins

There are multiple criteria for assessing the economic impact of mycotoxins on humans and on animals. Considerations include loss of human and animal life, health care and veterinary care costs, loss of livestock production, loss of forage crops and feeds, regulatory costs, and research cost focusing on relieving the impact and severity of the mycotoxin problem. The worldwide contamination of foods and feeds with mycotoxins is a significant problem. Extensive mycotoxin contamination is found in both developing and developed countries. Various studies have attempted to quantify the potential market losses associated with mycotoxins in crops. In the USA, it was estimated the total annual losses due to three mycotoxins – aflatoxin, fumonisin, and deoxynivalenol – to reach as high as US$ 1 billion. Almost all of this loss was borne by maize, groundnut, and wheat growers. However, a small portion of this loss was estimated to be suffered by livestock producers due to adverse animal health effects. It was estimated that 10 million dollars were lost in India’s export within a decade due to groundnut contamination with mycotoxins. If the current United States Food and Drug Administration (FDA) total aflatoxin action level of 20 μg/kg were adopted worldwide, total annual groundnut export losses for the USA, Argentina, China, and Africa would be US$ 92 million, whereas if an aflatoxin standard of 4 μg/kg were adopted worldwide, those total annual losses would increase to US$ 450 million.

Regulation of mycotoxins in foods and feeds
1.Good agricultural practices include (i) Early harvesting, (ii) Proper drying, (iii) Physical treatment, (iv) Sanitation, (v) Proper storage, (vi) Insect management and (vii) Othermethods.

2.Biological control: Significant inroads have been made in establishing various biocontrol strategies such as development of atoxigenic bio-control fungi that can out-compete their closely related, toxigenic strains in field environments, thus reducing the levels of mycotoxins in the crops.

3.Chemical control: Appropriate use of pesticides during the production process could help in minimizing the fungal infection or insect infestation of crops and consequently mycotoxin contamination.

4.Decontamination: Decontamination of food/feed contaminated with mycotoxins could be achieved through either chemoprotection or enterosorption.

5.Breeding for resistance: This is one of the most promising long-term strategies in mycotoxins contamination menace in Africa.
6.Legislation: Mycotoxin regulations have been established in about 100 countries, out of which 15 are African, to protect the consumer from the harmful effects of these mycotoxins.

7.Surveillance and awareness creation: This could be a long-term intervention strategy as has been advocated by WHO (2006).

Conclusion:

Mycotoxins can cause human and animal illness in different ways. Mycotoxins usually enter the body via ingestion of contaminated foods, but inhalation of toxigenic spores and direct dermal contact are also important routes. Mycotoxins cause toxigenic activities in sensitive species that include carcinogenicity, inhibition of protein synthesis, immunosuppression, dermal irritation, and other metabolic perturbations. In the absence of appropriate investigative criteria and reliable laboratory tests, the mycotoxicoses will remain diagnostically daunting diseases. Only with continued research on understanding the effects and modes of mycotoxin action in various species, have regulations and control strategies been forthcoming. It is, therefore, essential to look into ways and means of prevention and control of foodgrains from mycotoxins.