Mycotoxins and mycotoxicoses

Mycotoxin-containing plant products infected with mycotoxin-producing fungi

Mycotoxins and mycotoxicoses

  • Many grains and sometimes other seeds and also plant products such as bread, hay, purees, and rotting fruit are often infected or contaminated with one or more fungi that produce toxic compounds known as mycotoxins.
  • Animals or humans consuming such products may develop severe diseases of internal organs, the nervous system, and the circulatory system and may die.
  • Also, many pasture grasses are infected with certain endophytic fungi that grow internally in the plant and, although they do not seem to seriously damage the grass plants, they produce toxic compounds that cause severe diseases in the wild and domestic animals that eat the plants.
  • Similarly, toxic and sometimes lethal to animals are some grasses whose seeds are infected with bacteria carried there by a nematode; these bacteria are often themselves infected with a virus (bacteriophage) that induces the bacteria to produce compounds very toxic to animals.
  • Ergotism is an example of a mycotoxicosis caused by food and feed made extremely unhealthy by mycotoxins produced by the fungus Claviceps purpurea.
  • Ergotism causes very direct and dramatic symptoms and has been known for many centuries, if not millennia.
  • There have been, however, innumerable other cases in which people or animals became chronically or acutely ill by eating food or feed that contained unsuspected toxic substances.
  • The existence and identity of the toxic substances had remained unknown, the sources of such
    unsafe food and feed had been little noticed, and the ailments affecting humans and animals remained unexplained.
  • It was not until the 1960s that a severe disease of young turkey birds was shown to be caused by moldy feed and called attention to the importance of mycotoxins in the health of people and
    animals.
  • Mycotoxins are toxic fungal metabolites that are released by relatively few but universally present fungi growing on grains, legumes, and nuts.
  • Such produce, especially when harvested while still containing a high percentage of moisture or if it is damaged and stored at relatively high humidity, becomes moldy, i.e., it supports the growth of mycotoxin-producing fungi.
  • Such moldy produce is likely to carry high concentrations of mycotoxins.
  • Several of the mycotoxins are proven carcinogens, may disrupt the immune system, and may retard the growth of animals or humans that consume them.
  • Even very small amounts of mycotoxins bring about the detrimental effect of mycotoxins on the immune system and metabolism of humans and animals, thereby posing a continuous health hazard.
  • At higher concentration, which occur often on moldy produce, mycotoxins cause visible clinical symptoms (mycotoxicoses) in both humans and animals in the form of nervous agitation, dermal and subcutaneous lesions, impaired growth, damage to kidneys and liver, cancer, and others symptoms.
  • Although the last recorded outbreak of gangrenous ergotism occurred in Ethiopia in 1978, it was not until 1960 that the first general interest in mycotoxicoses was shown when the so-called “turkey X disease” appeared in farm animals in England.
  • It was eventually shown that the disease was caused by feed contaminated with aflatoxins, and when these were shown to cause cancer in the liver of humans and animals, interest in mycotoxins skyrocketed.
  • Aflatoxins are extremely toxic, appear in the milk of animals consuming contaminated feed, attack primarily the liver, and are mutagenic, teratogenic, and carcinogenic.
  • In the last several decades, several outbreaks of aflatoxicosis have occurred in tropical countries where many adults in rural populations often consume moldy corn.
  • Blood examinations in adults and children living in some tropical areas and showing various symptoms of varying intensity have revealed the presence of aflatoxins in them, with significant
    seasonal variations.
  • In addition to aflatoxins produced by the two aforementioned species of Aspergillus, several other equally toxic mycotoxins, e.g., ochratoxins, are produced by these and by other species of
    Aspergillus, by Penicillium, and by other fungi. Ochratoxins occur in cereals, coffee, bread, and in many preserved foods of animal origin.
  • About 20,000 people in the northern Balkans seem to be suffering from diseases caused by chronic exposure to ochratoxin.
  • Poisoning from moldy sugar cane is caused by a mycotoxin produced by species of Arthrinium, and in one rural area in China it affected more than 800 persons who had ingested moldy sugar cane.
  • Aspergillus and Penicillium are extremely common in nature and are almost always present to some extent in any feed and in most foods.
  • Aflatoxins are the most common mycotoxins, but even more potent mycotoxins, e.g., patulin, roquefortin C, and others, are also produced by species and strains of Penicillium.
  • A number of potent mycotoxins, the trichothecins, are produced by several species of Fusarium and, to a lesser extent, by species of Trichoderma, Trichothecium, Myrothecium, and Stachybotrys.
  • The most common trichothecin is deoxynivalenol, also known as vomitoxin.
  • Another type of mycotoxin, zearalenone, is produced by somewhat different species of Fusarium (F. graminearum). Vomitoxin and zearalenone often occur together, especially in scabby wheat and in corn infected with Gibberella ear rot, but they have also been found in moldy rice, cottonseed, flour,
    barley, malt, beer, and other foods.
  • In addition to humans, vomitoxin and zearalenone affect cattle, swine, chickens and other birds, cats, dogs, and fish.
  • Individuals fed contaminated food or feed over a period respond by vomiting, refusal to eat, suppression of their immune system, diarrhea, loss of weight, and low milk production in the case of
    cows.
  • A still different group of mycotoxins, called fumonisins, are produced by Fusarium verticillioides (F. moniliforme, F. proliferatum)and related species, primarily in corn and cornbased products.
  • Fumonisins affect all or most of the animals affected by the other Fusarium toxins but they also affect and are particularly toxic to horses.
  • In horses, low concentrations of fumonisins cause liquefaction of the brain, resulting in the “blind staggers” and “crazy horse disease” in which horses display blindness, head butting and pressing, constant circling and being agitated, and finally die.
  • In swine, fumonisin attacks the heart and the respiratory system, in which it causes swellings, and
    it also causes lesions in the liver and pancreas.
  • In humans, fumonisins have been linked to cancer.
  • In the last 10 years, outbreaks of fumonisins in feed or food have been reported in several states from
    Arizona to Virginia and from South Carolina to the upper Midwest and in some Canadian provinces.
  • In most of the cases just mentioned, most of the damage is caused by the mycotoxins in food or feed consumed by humans and animals. However, for people and animals spending considerable time surrounded by moldy food or feed, there is the added danger of directly breathing spores of these fungi.
  • It is not clear how detrimental to their health this is, but humans and animals, especially horses, exposed to spores of Stachybotrys chartarum develop irritation of the mouth, throat and nose, shock, skin necrosis, decrease in leukocytes, hemorrhage, nervous disorder, and death.
  • Stachybotrys grows on straw and feed and on moist surfaces on walls and in air-conditioning ducts and is considered one of the most important causes of the “sick building syndrome.”

Mycotoxins and mycotoxicoses

Leave a Comment

Your email address will not be published. Required fields are marked *