General Review of Mycotoxins

Dr.Kedar Karki

Mycotoxins

• Mycotoxins are secondary metabolites produced by fungi present in feed.

• Mycotoxin's production depends on fungus specie and strand, plant specie, environmental moisture and temperature, presence of pests, etc.

• Mycotoxins cause damages in feed quality. • Their incidence depends on geographical area and

season. • Mycotoxins are toxic: they produce mycotoxicosis and

drop of performance. • Their presence in feed can be reduced by applying

Hazard Analysis and Critical Control Points.

Mycotoxin toxicity

Main factors that influence toxicity of mycotoxins are:

• Bioavailability. • Combined effects between several mycotoxins. • Amount of mycotoxins consumed. Continuous or

intermittent ingestion of the contaminated feed. • Animal weight, age, physiological and health

status.

Mycotoxicosis

• Mycotoxicosis (1962, Forgacs and Carl): host's intoxication as a result of ingestion of a toxic substance of fungal origin.Some cases show evident symptoms that can be easily associated to mycotoxicosis.

• In the other hand, subclinical mycotoxicosis is only recognizable by drop of performance and health status.

• Susceptibility to mycotoxicosis depends on animal specie, age, sex and coexistence with other illness.

Mycotoxicosis can cause:

• NUTRITIONAL ASPECTS

• Feed consume decrease.

• Nutrient absorption decrease.

• HEALTH ASPECTS • Mycotoxicosis typical

of every mycotoxin.

• Immunosupression: arise of other pathologies.

MYCOTOXINS CLASSIFICATION AND MODE OF ACTION

• Lots of described mycotoxins.

• Varied molecular weights and structures: difficult to classify.

  • They keep associated to

fungus or substrate.

• Many of them are stable to chemical/physical treatments.

• Mycotoxins persist in food chain.

Classification according to pathology

Hepatotoxins: sporidesmine, aflatoxins, luteoskirin, cycloclorotin, rubratoxins, sterigmatocistin.

Nephrotoxins: ochratoxin, citrinin.

Neurotoxins: penitrem A, patulin, fumonisins, citreoviridin.

Toxins of intestinal tract: trichotecenes, T-2 toxin, deoxynivalenol (Don, Vomitoxin), HT2 toxin, fusarenone.

Steroidal; strogenic (Zearalenone), D vitamin analogous

Haemorrhagic and circulatory toxins: Ergot alkaloids, aflatoxins.

Classification according to chemical structure

Chemical structure

• Chemical structure determines:

• Mycotoxin's mode of action.

• Mycotoxin's method of detoxification

Chemical structure and mode of action Mode of action:

• specific biochemical interaction through which a substance produces its biological effect.

• In order to achieve a biological effect, an interaction with a receptor is essential.

Chemical structure and mode of action

• Chemical groups of the receptor must interact with chemical groups of the substance, that is, chemical structures in the binding point must be complementary.

KEY-LOCK MODEL

Mycotoxins with shared chemical structure may interact with the same receptors an thus have an alike biological effect.

Chemical structure and mode of action

• Into practice T2 toxin, HT2 toxin, deoxynivalenol, nivalenol have a sesquiterpene group in their structure and they all have necrotic effects on mucous membranes.

Chemical structure and mode of action

• B1, B2, G1, G2 aflatoxins, sterigmatocistin have cumarinic group in their structure and they all have haemorrhagic effects alike anticoagulant active principles used in human pharmacology: warfarine, acenocumarol. These active principles also show a cumarinic structure.

Aflatoxin B1

MYCOTOXIN ANALYSIS IN FEED MANUFACTURING

• Decision making in raw material purchasing

Usual methods of analysis

• Thin layer Chromatography (TLC).

• Liquid Chromatography (HPLC).

• Gas Chromatography-Mass spectrometry (GC-MS).

• Immunoassay(ELISA).

Maximum allowed concentration

• Gradually more countries legislate about mycotoxin limits in fodder and raw materials destined to animal nutrition.

Maximum concentrations are set depending on:• Mycotoxin's toxicity • Animal specie sensitivity and age • Fungi load characteristic of plant specie • Availability and limits of analysis method. • Maximum concentration for each mycotoxin depends on

every country.

Maximum allowed concentration

• Maximum concentration depends on animal specie and age and on raw material or fodder.

INTERPRETATION OF RESULTS

• Interpretation of results

Considering the results obtained in the lab, decisions are made taking into account:

• Concentration of each mycotoxin (individual effect). • Concentration of all mycotoxins analysed as a whole

(combined effects). • Possible bias of analysis. • Presence of non-analysed mycotoxins.

COMBINED EFFECTS

There are more possibilities of finding combined effects in

mycotoxins... • With similar molecular structure.

Synthesized by the same fungal strand or specie. Synthesized by the same fungal family.

The appearance of combined effects depends on:

• Concentration of each mycotoxin.

• Animal sensitivity (specie, age, health status).

Additive effect

• Combined effect of A and B mycotoxins is equal to the addition of the effect of each mycotoxins.

Additive effect

• Aflatoxins + DeoxynivalenolPoultry: decrease in proventriculus weight, increase of DHL enzyme, indicator of tissue damage.

• Aflatoxins + Cyclopiazonic acidPoultry: growth decrease. Pigs: feed intake and growth decrease; inflammation and necrosis of the gastrointestinal tract. hepatotoxicity.

Additive effect

• Aflatoxins + DiacetoxyscirpenolPig: Weight and growth decrease, alteration of blood parameters that indicates hepathotoxicity.

• Aflatoxins + MoniliforminPoultry: weight and efficiency decrease. Increase of heart's relative weight. Biochemical parameters indicate nephro and

Additive effect

• Citrinin + ochratoxin APig: nephrotoxicity. They affect transport of several molecules and protein synthesis.

• FusaricPoultry: feed consumption and growth decrease. Nephro and cardiotoxicity.

• Ochratoxin A + T-2 toxin Poultry: Weight decrease, increase of kidney, liver, proventriculus and gizzard relative weight. Nephro and hepatotoxicity.

Additive effect

• Fumonisin B1 + Diacetoxyscirpenol Turkey: Weight decrease. Hepatotoxicity.

• Fumonisin B1 + T-2 toxin Poultry: weight and efficiency decrease. Nephro and hepatotoxicity.

• Deoxynivalenol + MoliniformineTurkey: weight of kidney and heart increases. Tissular damage in myocardium.

Synergic effect

•Combined effect of A and B mycotoxins is higher than the addition of the effect of each mycotoxin.

Synergic effect

• Aflatoxins + Ochratoxin A Poultry: Weight decrease, mortality increase. Hepatotoxicity and severe nephrotoxicity.

• Aflatoxins + Toxin T-2 Very important because of its prevalence Poultry: weight decrease, increase of kidney, gizzard and heart relative weight; decrease of the medium corpuscular volume and of the potassium plasma levels.

Synergic effect

• Deoxynivalenol + Fumonisin B1Pigs: great weight decrease.

• Deoxynivalenol + Zearalenone Pigs: theratogenesis in piglets.

Antagonistic effects

• Combined effect of A and B mycotoxins is less than the addition of the effect of each mycotoxin. (but higher than the effect of each mycotoxin separately).

Antagonistic effects

• Citrinin + ochratoxin APoultry: the presence of these mycotoxins together reduces the toxic effects of the mycotoxins separately (growth and water consumption decrease).

• Aflatoxins + diacetoxyscirpenol Poultry: the presence of these myocotoxins together reduces the toxic effects of the mycotoxins separately (growth and feed consumption decrease).

BIAS OF THE ANALYTICAL METHOD

• 1. Not representative samplingSample not representative, because of the big sample size or the king of storage/container of the raw material.

2. Not validated analysis methodAnalysis method should have been validated by a prestigious institution like International Organization for Standardization (ISO).

3. Low quality standards Trouble to get mycotoxin standards in some countries. % recovery of solid standards by dissolution <100%.Standard solution not stable.

4. Procedure for sample extraction

PRESENCE OF NON-ANALYSED MYCOTOXINS

• Not-analysed mycotoxins

In raw materials there could be mycotoxins whose are not analysed:

1. WELL-KNOWN MYCOTOXINS Whose analysis is not performed because of economic reasons, lack of validated methods, presence unlikely, etc.

2. LITTLE-KNOWN MYCOTOXINS Mycotoxins whose incidence and effects are little known.

THERE ARE MORE THAN 300 DESCRIBED MYCOTOXINS

Reference:

• Interpretation of the results of mycotoxin's analysis in feed

• Author: Paper Presented at Biovet Symposium 2007 (Courtesy of Biovet SA)