aflatoxin - Contamination conditions, Pathology, Detection of aflatoxin in humans, Major types of aflatoxins and their metabolites

A toxin produced by the mould Aspergillus flavus (from Aspergillus flavus toxin) commonly found in groundnuts (peanuts), cottonseed, soybeans, wheat, barley, sorghum, and nuts such as pistachios, almonds, and cacao, where the climate favours its growth. The major epidemic of ‘Turkey-X disease’ in turkeys in the USA in 1960 was caused by feeding with contaminated groundnuts. Symptoms of poisoning include weight loss, loss of co-ordination, convulsions, and death. It also damages the liver, and causes liver tumours when fed long-term at low doses.

Aflatoxins are naturally occurring mycotoxins that are produced by many species of Aspergillus, a fungus, most notably Aspergillus flavus and Aspergillus parasiticus. After entering the body, aflatoxins are metabolized by the liver to an reactive intermediate, aflatoxin M1, an epoxide.

Contamination conditions

Aspergillus is common and widespread in nature and are most often found when crops are exposed to a high humidity environment over a long period of time or are damaged in stressful conditions such as drought, a condition which lowers the barrier to entry.

Virtually all sources of commercial peanut butter contain minute quantities of aflatoxin, but it is usually far below the US Food and Drug Administration's (FDA) recommended safe level.

In 1989, Saddam Hussein ordered the government of Iraq to begin production of aflatoxin as an economic biological/chemical weapon.

Pathology

High-level aflatoxin exposure produces an acute necrosis, cirrhosis, and carcinoma of the liver exhibited by hemorrhage, acute liver damage, edema, alteration in digestion, and absorption and/or metabolism of nutrients.

No animal species is immune to the acute toxic effects of aflatoxins including humans; however, humans have an extraordinarily high tolerance for aflatoxin exposure and rarely succumb to acute aflatoxicosis. Children, however, are particularly affected by aflatoxin exposure which leads to stunted growth and delayed development. Chronic exposure also leads to a high risk of developing liver cancer, as the metabolite Aflatoxin M1 can intercalate into DNA and alkylate the bases through its epoxide moiety.

Detection of aflatoxin in humans

There are two techniques that have been used most often to detect levels of aflatoxin in humans. Presence of this breakdown product indicates exposure to aflatoxin in the past 24 hours.

Major types of aflatoxins and their metabolites

At least 13 different types of aflatoxin are produced in nature. Aflatoxin B1 is considered the most toxic and is produced by both Aspergillus flavus and Aspergillus parasiticus. While the presence of Aspergillus in food products does not always indicate harmful levels of aflatoxin are also present, it does imply a significant risk in consumption of that product. Aflatoxin M1 : metabolite of Aflatoxin B1 in humans and animals (exposure in ng can come from mother's milk).

Interaction of aflatoxin with the Hepatitis B virus

Studies have shown that concurrent infection with the Hepatitis B virus (HBV) during aflatoxin exposure increases the risk of hepatocellular carcinoma (HCC). As HBV interferes with the ability of hepatocytes to metabolize aflatoxins, an aflatoxin M1-DNA conjugate exists for a longer period of time in the liver, increasing the probability of damage to oncogenes such as p53. This effect is synergistic with the resulting damage far greater than just the sum of aflatoxin or HBV individually. (Williams, 2004)

Decreasing HBV infection levels through vaccination is an effective and simple approach that can be taken to reduce these harmful synergistic effects, thus decreasing the impact of chronic aflatoxin exposure. This strategy may prove to be highly effective – many regions of the world which have high aflatoxin rates, such as western Africa and China, also have high HBV infection rates.