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Polymycotoxicosis: Evaluation of its Effects

Published: November 4, 2014
By: Kryukov V.S. Professor, Doctor of Biological Science
In scientific publications in the 1980s – 1990s you can find information about the spreading of mycotoxins. But since then, cultivars and agricultural technology have changed, methods of grain storage and grain processing have improved due to the overall progress. Between January 2009 and December 2011, Austrian researchers selected 7049 samples of grain from different continents. The samples were analyzed for the occurrence of aflatoxins (AFB), zearalenone (ZEN), deoxynivalenol (DON), fumonisins (FUM) and ochratoxin A (OTA) by all modern methods. Researchers performed 23,781 mycotoxin analyzes in all. AFB, ZEN, DON, FUM and OTA were present respectively in 33%, 45%, 59% 64% and 28% of analyzed samples. Thereby, grain and feed in the word are more frequently contaminated with deoxynivalenol and fumonisin. From the 7049 samples, only 19% of them tested negative for the presence of the five analyzed mycotoxins (but it doesn’t rule out the possibility of the presence of other mycotoxins). 33% of samples showed the presence of one of the five mycotoxins, and two or more of the tested mycotoxins were present in 48% of the commodities.
In America, analysis showed that 10% of finished feed tested was below the limit of detection for all analyzed mycotoxins. 50% tested positive for the presence of one mycotoxin, and in 40% of the samples, two or more mycotoxins were present. In Europe, 39% of the finished feed samples analyzed tested positive for 2 or more mycotoxins, 37% tested positive for one mycotoxin. In Asia, 82% of finished feed were contaminated with two or more toxins, 12% - with one, and only 6% of feed tested below the limit of detection for mycotoxins. (RodriguesI.and Naehrer K. 2012).
According to the results of these researches, more than 76% of feed are affected by mycotoxins. In America and Europe, 39 - 40% of feed contained several mycotoxins. In Asia, it increased to 82%. The results shows that polymycotoxicosis poses a real threat.
The microscopic funguses called mould or mould funguses are part of an ecosystem. They are widespread in the nature. The grain raw materials are often contaminated by several mycotoxins. The first stage of infection of grain (and roughage) occurs in the field by so-called field fungus. Field fungus is a different type of the genus Fusarium.
As a result, the grain harvested from a field contains various amounts of trichothecene mycotoxins and other ones to a lesser extent. Field funguses die off after grain drying and transfer in storage. But the mycotoxins formed before don't disappear. Storage mould or storage fungus goes on changing by field fungus. As a result, grain will contain some tens of mycotoxins. Their concentration can be so extremely low (at the level of the minimal threshold of detection), and so high that it’s capable of causing poisonings and even death in animals. Therefore, it would be correct to speak about doses of mycotoxins in raw materials and not about raw materials free from mycotoxins. 
In this connection, veterinary and human medicine experts defined relatively harmless doses for most studied toxins. The maximum doses which don't cause negative changes are called "maximum residue limits" (MRL) of toxin in raw materials or in feed. In Russia, the expression "maximum concentration limit" (MCL) is more common. MRL is often expressed in ppb or ppm that is equivalent of mkg or mg per 1 kg. Individual MCL exists for each toxin: Aflatoxin B1- 0,02; Ochratoxin A - 0,05; Sterigmatotsistin - 0,1; T-2 Toxin - 0,1; Deoxynivalenol (Vomitoxin) - 2,0; Zearalenone - 2,0 mg in1 kg of a feed.MCL depends on age, physiological condition and the kind of animal. Pigs are the most sensitive to mycotoxins among animals. The cows are less and the poultry are the least of all. Moreover, if several mycotoxins are detected in feed it is necessary to consider the interaction of mycotoxins on an organism during the course of metabolism. Comprehensive recent review on this question was published in Feedstuffs in 2011.  
Polymycotoxicosis: Evaluation of its Effects - Image 1
MCL is defined by researches: scientists add only one studied mycotoxin (with purity of a preparation 95 - 99%) to feed which doesn’t contain other mycotoxins. Schematically process looks as follows: several groups of animals are fed by feed with increasing concentration of mycotoxin. Then scientists reveal the group of animals in whom the maximum dose of the added toxin didn't cause registered changes. The content of toxin in feed of this group would be MCL(maximum concentration limit). If animals consume feed with the content of toxin below maximum concentration limit, mycotoxin is subjected to transformations by system of a metabolism of xenobiotics (foreign substances for an organism) like drugs, antibiotics, synthetic antioxidants, colouring agentand some other substances (Park D., 1985; Sheweita  S. A., 2000; Galtier P. et al., 2008).
The system of protection against foreign substances inactivates different foreign substances at different speed. At the first stage foreign (toxic) substance is oxidized with the addition of hydroxyl group and becomes water-soluble. Toxicity of initial substance decreases at this stage. The formed metabolite can be excreted through kidneys or the reactions of conjugation can occur. As a result, the substance loses toxicity and it’s easily excreted in the urine. The endogenous detoxication (metabolism) of various mycotoxins proceeds with unequal speed and it varies in different types of animals for the same toxin (Adav S.S. Govindwar S.P.  1997). VariousMCLfor separate mycotoxins are partly defined by this occurrence. It is important to know that this system has limited opportunities on a detoxication which influenceMCL.
As mentioned before,MCL(maximum concentration limits) is defined in using only one pure mycotoxin. But in natural conditions mycotoxicosis caused by one mycotoxin can’t exist – as a fact polymycotoxicosis are found more frequently. In current practice, laboratories define separate concrete mycotoxins. However, it is necessary to observe that formation of mycotoxins presents multistage process in fungus cells. Synthesis products at penultimate stages (pretoxins) possess toxicity too but this one is weaker. Therefore if mycotoxins in the feed are detected at the level of MCL, their negative effect will be stronger due to the additional influence of its pretoxins. Its characteristics haven´t been studied and they haven’t been defined in laboratories yet.
At the same time mycotoxins and pretoxins will be inactivated by the same system of protection of an organism from foreign substances, they’ll create additional load on it. 
So how to consider the influence on animals by polymycotoxicosis if sizes ofMCLfor different substances differ so much?
Let's take a look at the following example. Several mycotoxins were revealed in complete feeds for broilers. Concentration of mycotoxins didn't exceedMCL(table 1).
Results of the analysis of complete feeds on the content of mycotoxins: 
Mycotoxins
(mg/kg)
Complete feeds
Starter
Grower
MCL
B1 aflatoxin
0, 02
0, 005
0,025
Deoxynivalenol
0,40
0,54
1,0
T-2 toxin
0,04
0,042
0,1
Ochratoxin A
0,004
0,004
0,01
Fumonisin
1,0
3,5
5,0
  Sum of toxins,  mg/kg
1,464
4,091
  -
Concentration of each separate mycotoxin didn't exceed the fixed sizesMCLaccording to existing regulatory documents and, therefore, it is possible to conclude that the feed is quite safe. However, according to the fact that mycotoxins are inactivated in an organism by one system of a metabolism of xenobiotics, load of this system will increase because of the presence of several mycotoxins in feed.
Drugs, especially antibiotics, will increase this load. And the ability of the system to inactivate each separate mycotoxins (and drugs) will decrease. So how to estimate the influence of that feed on animals? The total of mycotoxins in a starter is 1,464 mg/kg and in a grower is 4,091 mg/kg. They are strongly different. The increase in the total of mycotoxins in the feed is caused by increasing fumonisin on 2,5 mg/kg or by 3,5 times, but it was still lower thanMCL. At the same time if concentration of T-2 toxin or other mycotoxin with lowMCLincreased even on 0,5 mg/kg, the feed wouldn’t be suitable for feeding. Therefore, total of weight amounts of mycotoxins in a feed doesn't give the grounds for its objective assessment. Let us accept the MRLs for a unit operates independently of the mass values of this quantity for each mycotoxin and then content weight values of mycotoxins in the same feed into parts ofMCL(table 2)
The content of mycotoxins in the complete feed, expressed in parts of MCL: 
Mycotoxins into parts ofMCL
Complete feeds
Starter
Grower
Aflatoxin B1
0, 8
0, 2
Deoxynivalenol
0,4
0,54
T-2 toxin
0,4
0,42
Ochratoxin A
0,4
0,4
Fumonisins
0,2
0,7
Sum of toxins on MCLs
2.2
2,26
According to the calculations given in the table, we can conclude that toxicity of feeds on the sum of the parts of MCLwas identical and exceeded unit. In researches of pure mycotoxins (80 years of last century) it was established that they mutually strengthen influence of each other at joint presence at the feed (Adav S.S. Govindwar S.P. 1997; Ramsdell H. S. and Eaton D. L. 1990)  and total negative effect will be higher, than sum of content of mycotoxins in parts of MCL. This is an explanation of the point of view of biochemistry about the transformation of mycotoxins in an organism. In practice in feed, except revealed mycotoxins, there are always incomplete products of their synthesis (pretoxins) which also create load of system of an endogenous detoxication. They strengthen negative influence on animals but their effect can't be quantitatively considered.
In conclusion, we want to note that the assessment of feeds or feed raw materials on separately taken mycotoxins doesn't give a full picture for an assessment of potential danger. It’s necessary to summarize parts ofMCLon each mycotoxin found in feed. The negative effect of mycotoxins revealed by scientific researches ofMCLduring estimation will be always lower, than the same sum of mycotoxins of a natural origin. 
References:
  1. Adav S.S., Govindwar S.P.  Effects of aflatoxin B1 on liver microsomal enzymes in different strains of chickens. Comp Biochem Physiol C Pharmacol Toxicol Endocrinol. 1997. Vol.118 (2). Pp.185-189.
  2. Galtier P., Meissonnier G., Joelle Laffitte, Isabelle P. Oswald, Loisea N.. Molecular interactions between mycotoxins and liver enzymes involved in drug metabolism in rodents and farm animals. 2008. Krmiva 50Zagreb, 4; Pp. 205-213.
  3. Park D. The metabolism of foreign compounds.1985
  4. Pedrosa K., Borutova R. Synergistic effects of mycotoxins discussed. Feedstuffs 2011. 9th of May.
  5. Ramsdell H. S., EatonD. L. Species susceptibility to aflatoxin B1 carcinogenesis: comparative kinetics of microsomal biotransformation. Cancer research. 1990. Vol.50. Pp. 615-620.
  6. RodriguesI., Naehrer K. A Three-Year Survey on the Worldwide Occurrence of Mycotoxins in Feedstuffs and Feed. Toxins. 2012. Vol.4. Pp. 663-675.
  7. Sheweita  S. A. Drug-Metabolizing Enzymes: Mechanisms and Functions, Current Drug Metabolism. 2000. Vol.1. Pp. 107-132.
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Authors:
Dr Valeriy Kryukov
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