Mycotoxins & Aflatoxins: Health Risks, Diagnosis & Manage...

MYCOTOXINS, DIAGNOSIS & ANTIFUNGAL AGENTS --- SECTION 7: MYCOTOXINS Definition Mycotoxin — toxic secondary metabolites produced by fungi Low molecular weight compounds with diverse chemical structures and biological activities Mycotoxicosis — disease caused by mycotoxin action; mediated through liver, kidney, lungs, nervous, endocrine and immune systems At least 25% of the world's agricultural products are contaminated with mycotoxins Effects: acute and chronic toxicity, carcinogenic, mutagenic, genotoxic, immunotoxic Historical Perspective Modern mycotoxicology began with discovery of aflatoxins in early 1960s as the cause of "Turkey X disease" — killed 10,000 turkeys fed contaminated peanut meal --- Toxicogenic Fungi — Main Genera Most mycotoxin-producing fungi belong to three genera: Aspergillus Fusarium Penicillium Field fungi (contaminate crops before harvest): A. flavus , Alternaria longipes , Claviceps purpurea , Fusarium verticillioides , F. graminearum Harvest fungi : F. sporotrichioides , Stachybotrys atra , Myrothecium verrucaria , Trichothecium roseum Storage fungi : Penicillium citrinum , P. cyclopium , P. expansum , A. parasiticus , A. flavus , A. ochraceus , Fusarium verticillioides --- Factors Affecting Mycotoxin Production Environmental: weather conditions, plant stress, invertebrate vectors, microbial competition, geographic and seasonal factors Physical: temperature (optimal 24–28°C ; T-2 toxin produced at 15°C), humidity, water activity, insect damage, time of exposure Chemical: nutritional status of crops, fungicides used in crop management Storage factors: water activity (aw), temperature, aeration (O2/CO2 levels), pH, presence/absence of specific nutrients and inhibitors. Ecological succession of different fungi occurs as temperature and water activity of stored grain changes. --- Characteristics of Mycotoxin-Induced Disease Not always transmitted between animals Pharmaceutical treatment does not alter the course of disease Most often presents as uncertain, sub-acute or chronic condition No specific treatment for most mycotoxins Supportive treatment: vitamins and selenium supplementation --- THE MAJOR MYCOTOXINS 1. Aflatoxins Produced by: Aspergillus flavus (most common), A. parasiticus , A. pseudotamarii , A. nomius Affected crops: Corn, peanuts, tobacco, oilseeds, dried fruits, cotton seeds, rice, pepper Types: B1, B2 — blue fluorescence under UV light (cyclopentane E-ring) G1, G2 — green fluorescence under UV light (xanthone ring) M1 — hydroxylated metabolite of AFB1; found in milk, urine and tissues of animals fed contaminated feed; ~10 times less toxic than AFB1 AFB1 is the most toxic and one of the most potent naturally occurring carcinogens ; main target organ = liver Factors favouring production: Warm temperature: 28–33°C High moisture content Toxicity: Young animals more susceptible than adults Nutritional deficiency increases susceptibility Teratogenic — disturbs foetal development Hepatocellular carcinoma (chronic exposure) Liver damage in poultry, fish, rodents, non-human primates AFB1 also affects lungs and respiratory system Clinical signs: decreased growth rate, reduced feed efficiency, mild anaemia, increased susceptibility to infectious disease Treatment: Detoxification: Hydrated sodium calcium aluminosilicate (HSCAS) absorbs aflatoxins Supportive: Vitamin E and selenium Prevention: mould inhibitor — treatment of grain with anhydrous ammonia for 10–14 days --- 2. Zearalenone (RAL / F-2 Mycotoxin) Produced by: Fusarium roseum ( F. graminearum/Gibberella zeae ), F. equisetti , F. cerealis , F. verticilloides , F. incarnatum Affected crops: Corn, wheat, barley, oats, rice, sorghum Factors favouring production: High moisture level: 22–25% Alternating high and low temperatures: 7–21°C Mechanism: Potent estrogenic metabolite — binds to estrogen receptors → infertility, abortion, breeding problems. Functions as a weak oestrogen Most susceptible: Swine Clinical signs: Infertility, abortion, vulval swelling/prolapse, mammary enlargement Treatment: Remove contaminated feed; provide clean feed Animals return to normal within 1–4 weeks Surgical intervention may be needed for prolapsed vulvae/rectums --- 3. Ergot Alkaloids Produced by: Claviceps purpurea (most prominent ergot fungus) Crops affected: Rye, barley, wheat, oats (pathogens of grass species) Conditions favouring: Warm and humid conditions Disease: Ergotism (St. Anthony's Fire) Two types: Gangrenous ergotism — vasoconstriction → reduced blood supply to extremities → necrosis of feet, ears, tail; abortion Convulsive ergotism — CNS effects → suppressed lactation, hypersensitivity, ataxia (abnormal movement), increased temperature/pulse/respiration, hyper-excitability, tremors, heat intolerance Mechanism: Potent initiators of smooth muscle contraction Mimic the action of dopamine (neurotransmitter) Treatment: Warm, clean, stress-free environment Control secondary bacterial infection Milk supplement IV/intra-arterial infusio