Mycotoxins

Filamentous fungal metabolites that cause human or veterinary diseases are called mycotoxins. The mycotoxins that have received the most attention are the aflatoxins, a family of highly toxic, mutagenic, and carcinogenic compounds produced by certain strains of A. flavus, Aspergillus nomius, and A. parasiticus. These species regularly contaminate peanuts, corn, cottonseed, rice, tree nuts, and other agricultural commodities (28). A large body of epi-demiological and molecular biological data implicates af-latoxin with human liver cancer (29). Acute human afla-toxicosis, however, is rare and usually only occurs when famine or poverty forces people to subsist on moldy foodstuffs. On the other hand, veterinary aflatoxicosis is a major problem, with poultry and trout being particularly susceptible.

Other mycotoxins produced by members of the genus Aspergillus tend to be produced at toxicologically less im-

portant levels. These include cyclopiazonic acid (A. flavus), patulin (A. clavatus), and sterigmatocystin (A. nidulans and Aspergillus versicolor). The toxigenic potential of Aspergillus ochraceus is particularly varied, with different strains reported to make ochratoxin, citrinin, xanthomeg-nin, viomellein, and penicillic acid. Like aflatoxin, patulin and sterigmatocystin are carcinogenic; citrinin and ochra-toxin A are nephroxic; cyclopiazonic acid is a neurotoxin; and xanthomegnin and viomellein have been associated with photosensitization and liver damage. Many of the compounds classified as cytotoxic or neurotoxic in vertebrates also show toxicity against insects. Sclerotia have been a particularly rich source of metabolites with insec-ticidal properties (30).

Mycotoxin contamination varies from year to year based on weather, agricultural practices, storage conditions, and other factors. Aflatoxin is usually worst in drought years. International agencies have set levels for permissible standards of contamination (31).

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