Detailed Explanation of the Pathogenic Characteristics of Duck Aflatoxin
(1) Production of aflatoxin Aflatoxin, like other mycotoxins, is one of the metabolic products produced by toxigenic fungi during their growth and reproduction in a substrate. This toxin was discovered in 1960 during the investigation of the cause of "Turkey X disease" that affected 100,000 turkeys in the United Kingdom. The following year, it was further found that peanut meal contaminated with Aspergillus flavus could induce liver cancer in rats, confirming that aflatoxin is a carcinogenic mycotoxin. The main fungi producing aflatoxin are specific strains of Aspergillus flavus and Aspergillus parasiticus, while Aspergillus wentii and Penicillium puberulum can also produce small amounts. According to Eslaer's report, 80% of strains of the first two fungi growing on substrates such as corn in tropical regions can produce aflatoxin (Aspergillus flavus mainly produces B1 and B2, while Aspergillus parasiticus produces B1, B2, G1 and G2); in temperate and cold regions, even though closely related strains of the same genus grow on the same substrates, the detection rate of toxigenic strains is greatly reduced. Of course, in addition to the above regional differences, the most suitable conditions for toxin production are: substrate moisture content should be above 16%, relative humidity should be between 80%-90% (Aspergillus flavus is one of the mesophilic fungi), temperature should be 25-30°C, and oxygen content should be no less than 1%. At the same time, the substrate on which it grows must be agricultural products rich in carbohydrates, among which rice, wheat, corn, peanuts, cottonseed and other grain and oil crops are ideal, as they are prone to mold growth and aflatoxin production.
(2) Types of aflatoxin Aflatoxin is a class of compounds with similar structures and possessing a difurofuran ring-oxonaphthalenone, namely difurofuran ring-coumarin. Based on the fluorescence color emitted on thin-layer plates under 365 nanometer (nm) ultraviolet light (B1 and B2 appear blue-purple, G1 and G2 appear yellow-green), Rf values (i.e., migration rate on thin-layer plates), and their chemical structures, they are named B1, B2, G1, G2, M1, M2, P1, Q1, toxic alcohol and GM1, totaling 18 types. Among them, except for B1, B2, G1 and G2 which are naturally produced, the rest are derivatives.
Aflatoxin is resistant to high temperatures and is minimally destroyed at normal disinfection temperatures; it can only be decomposed and destroyed at 280-300°C. However, it is easily destroyed by strong alkalis or strong oxidizing agents, and can also be destroyed under ultraviolet light (over a long period).
Aflatoxin has low solubility in water and is easily soluble in some organic solvents such as chloroform, methanol and ethanol, but insoluble in hexane, diethyl ether and petroleum ether. Currently, the detection method for aflatoxin in various foods, grains and oils, feeds and forages in China uses thin-layer chromatography (TLC).
(3) Toxicity of aflatoxin There are differences in the toxicity levels among aflatoxins; for example, the toxicity of B1 is successively greater than that of G1 and M1 by 2 times, B2 by 4 times, and G2 by 8 times. Among livestock and poultry, in addition to male animals being more prone to aflatoxin poisoning than females, young animals are more sensitive than adult animals. The order of sensitivity of poultry to aflatoxin is: ducklings > turkey poults > chicks > Japanese quail.
Animal experiments have proven that the target organ of aflatoxin is the liver, making it a hepatotoxin. Regarding liver damage caused by aflatoxin, if it is only a single low dose, the liver lesions can still recover; if a large dose or repeated exposure to the toxin occurs, the liver lesions often turn into a chronic pathological process.
(4) Carcinogenicity of aflatoxin Carcinogenic aflatoxin, like other chemical carcinogens, undergoes biological metabolism to form ultimate carcinogens that bind with macromolecules such as DNA, thereby exhibiting carcinogenicity. Aflatoxin not only induces liver cancer in test animals, but can also induce tumors in other organs or sites, such as gastric adenocarcinoma, kidney cancer, rectal cancer, breast cancer, ovarian tumors and small intestine tumors. Aflatoxin injected into test animals via the trachea can also induce tracheal squamous cell carcinoma.
Aflatoxin also has teratogenicity; in hamsters at 8-11 days of gestation, intraperitoneal injection of aflatoxin can induce malformations such as anencephaly, microcephaly, cardiac ectopia and other defects.