The mycotoxin HT-2. Until what point, will be or will not be important as undesirable substance in the animal feeding?

The HT-2 toxin belongs to the group A of the trichotecene toxins. These mycotoxins are produced by molds of the genus Fusarium, such as, Fusarium tricinctum, F.nivale, F.roseum, F.graminearum, F.solani, F.oxysporum, F.lateritium, F.sporotrichioides, F.rigidiusculum, F.episphaeria and F.poae. Other molds also can produce trichotecene toxins, such as, Cephalosporium crotocigenum, Myrotecium verrucaria, Stachybotrys atra, Calonectria nivalis, Trichoderma viride, Tricotecium roseum and Gibberella saubinetti.

Fusarium is a genus of mold that is part of the field flora (fitopathogenic substrates, live plants) and intermediate flora (cereal substrates recently harvested and still wet). This mold grows between 6 and 40º C with optimum growth between 18 and 30º C. It is aerobic and needs generally, an activity of water (aw) upper to 0.88 to grow and proliferate and upper to 0.91 to produce mycotoxins.

There are more of 40 derivative trichothecenes compounds, however those that are more significant as natural contaminants at the moment and are considered more important due mycotoxicosis problems in the animals are: T2 toxin (T-2) and diacetoxyscirpenol (DAS), which belong also to the group A, and the vomitoxin or deoxynivalenol (DON) that belongs to the group B of the trichothecene mycotoxins.
The trichothecenes receive their name from the tetracyclic 12, 13-epoxytrichotec-9-eno skeleton, in their molecule,

Trichothecene mycotoxins can be found as natural contaminants in cereals (corn, barley, sorghum, oat, wheat, rice, rye, millet) and his by-products.

The main problem is the gastroenteric syndrome. In general, the toxicological properties of these mycotoxins, it depends on the affected animal species, are: 1. Vomiting, diarrhoea, tachycardia. 2. Bleeding, edema, necrosis of skin tissues. 3. Hemorrhages of the epithelial mucosa of the stomach and intestine. 4. Hematopoietic tissue destruction. 5. Decrease in circulating white cells and platelets. 6. Hemorrhagic meninges (brain). 7. Nervous system disorder. 8. Rejection of the feed. 9. Necrotic lesions in different parts of the mouth. 10. Pathological degeneration of cells in the bone marrow, lymph nodes, and intestine.

The systems and organs affected are the digestive system, nervous, circulatory and skin. The trichothecene mycotoxins have potent immunosuppressive activity.

The main toxic effects of trichothecenes mycotoxins are produced at a cellular level. These mycotoxins inhibit the protein synthesis followed by an interruption of DNA and RNA synthesis. A cell division in the gastrointestinal tract membrane, the skin, lymphoid cells and erythrocytes, is produced. Acute problems in the gastrointestinal tract, bone marrow degeneration, and a significant inhibition of the immune system, are produced. There can also be hemorrhaging of the stomach and intestinal mucosa and a destruction of the hematopoietic tissue.

Taking into account that trichothecenes mycotoxins have a high alkalinity, especially T-2 toxin and diacetoxyscirpenol, the problem of oral lesions is attributed to contaminated feed which adheres primarily to the oral region due to the high moisture in this area and alkalinity provokes the already mentioned problem.

The typical oral lesions in poultry consist of a proliferation of caseous white-yellowish plates (albuminoide substance). These oral lesions appear most frequently in the superior and inferior areas of the beak, palatal, mouth, and tongue mucosa. Oral erosions are characteristic of trichothecene mycotoxins (especially with T-2 toxin and diacetoxyscirpenol) exposure. They can also produce serious lesions in the gizzard of poultry.
Evidently, the severity of the lesions becomes more serious the longer the animals are exposed to the mycotoxin.

Affected chickens can suffer from delayed growth, abnormal feathering, regression of the bursa of Fabricius, and anemia. Laying hens exposed to this mycotoxin suffer oral lesions, reduced feed intake, egg production, and deterioration of the eggshell quality of the eggs, with a significant increase in soft-shell eggs.
The feathering problems produced by these mycotoxins can be explained by epidermis necrosis and feathering follicle necrosis, as well as protein synthesis inhibition.

Inside the trichothecene mycotoxins of the group A, the studies of toxicity carried out until now for T-2 and DAS, are many and varied in animal species such as poultry and pigs, some of them indicated and referred as bibliographical review (Mirocha, 1979; Leeson et al, 1995; Gimeno, 2003; Gimeno and Martins, 2003; Gimeno and Martins, 2006). However there are very few scientific published studies, at the moment, on the toxicity of HT-2 toxin (HT-2) in these animal species.

2.- HT-2 toxin mycotoxicosis in chickens

2.1.- We would like to show the acute toxicity of the HT-2 regarding the mortality in 1-day-old broiler chicks (body weight range of 40 ± 3 g) and the negative effects on body weight gain and feed consumption, corresponding to an acute mycotoxicosis, by the supply of a single oral doses of mycotoxin (mg/Kg body weight). Most deaths in mycotoxin-treated chicks occurred during the period of 8 to 60 h after dosing.  A comparison with the T-2 and DAS acute toxicity in the same conditions above indicated, will be done (Chi et al, 1978)

Table 1. Mortality, body weight gain, and feed consumption of 1-day-old broiler chicks administered single oral doses of  HT-2 toxin, T-2 toxin and diacetoxyscirpenol

* Adapted of Chi et al, 1978
** Mortality during the 7-day period after dosing.
*** Weight gain and feed consumption for surviving chicks during the 7-day period alter dosing.

Chicks treated with each trichothecene mycotoxin developed clinical signs of asthenia, inappetence diarrhea and coma within 4 to 10h after dosing (Chi et al, 1978).

It is clear that T-2 and DAS were more toxic than HT-2, whereas doses of T-2 and DAS of 8.7 and 6.8 mg/Kg body weight, respectively, caused 100% of deaths and on the other hand to cause the same percentage of deaths it was necessary a  HT-2 dose of 11.9 mg/Kg body weight.

2.2.- About the chronic toxicity caused by feed contaminated with HT-2, we have very recent data (Weber et al, 2010). However the study was done with combined contamination of T-2 and HT-2 in chickens.
Feed chickens starter (0-21 days old) was contaminated with 1040 ppb (micrograms/Kg) T-2 and 490 ppb HT-2 and finisher diet (22-39 days old)  was contaminated with 120 ppb T-2 and 20 ppb HT-2, for each group of chickens there was a control group and the total chickens were 40.
Pathological signs of toxicity were investigated on days 21 and 39 of the trial. Five chickens from each group were sacrificed on the 21st  and 39th  days of treatment. Lesions in the oral cavity and on the tongue and inflammation in the small intestine were found. Body weight was significantly lower in the chickens that were fed the contaminated diets, in comparison with the control group. Blood, liver and kidney samples were taken from the sacrificed chickens and was observed that the contamination did not cause a significant increase of malondialdehyde (very important biomarker for evaluating the lipid peroxidation process) content in the analyzed tissues.
Reduced glutathione content (GSH) was significantly lower in the liver on day 39th in comparison with that of the control group.
Gluthatione peroxidase activity was significantly higher in the liver of chickens feeding the contaminated diet than that of the control group (Weber et al, 2010).

Reduced glutathione (GSH) is a tripeptide that is present in high concentrations inside the erythrocyte. The GSH protects to the cell against the action of endogenous and exogenous oxidizers agents and maintains the membrane stability, it participates in the maintenance of the hemoglobin structure, in the  reticulocytes protein synthesis and preserves the integrity of some enzymes and proteins of the membrane.

We don't know what would have happened with HT-2 individual contaminations. However, we know what happens with the T-2 individual contaminations with those concentrations, being the effects similar to those ones previously mentioned (Mirocha, 1979; Leeson et al, 1995; Gimeno, 2003; Gimeno and Martins, 2003; Gimeno and Martins, 2006).

T-2 toxin: 4.97-5.25; DAS (4,15 DAS): 3.82 and HT-2 toxin: 7.22. (Leeson et al, 1995)

We have not found, at the moment, data of scientific studies on the chronic HT-2 toxicity in other poultry and/or animal species.  

On August 2006, in the Official Journal of the European Union (see bibliography), guidance values of maximum contamination concentrations with deoxynivalenol (vomitoxin), zearalenone, ocratoxin A and fumonisins B1+B2 in products intended for animal feeding, were published.
Regarding  HT-2 and T-2, the document says textually:
“Data on the presence of T-2 and HT-2 toxins in products intended for animal feeding are at present very limited. There is also an urgent need for the development and validation of a sensitive method of analysis. However there are indications that the presence of T-2 and HT-2 in products intended for animal feeding could be a reason for concern. Therefore, it is necessary to develop a sensitive method of analysis, collect more occurrence data, and carry out further investigations and research into the factors involved in the presence
of T-2 and HT-2 in cereal and cereal products, in particular in oats and oat products.
Taking into account the conclusions of the scientific opinions referred to in recital 1, and the lack of reliable data on T-2 and HT-2 toxins, together with the large year-to-year variation in occurrence of these mycotoxins, it is appropriate to collect more data on these mycotoxins in the different feed materials and feedingstuffs, in addition to the data already available from the coordinated control programmes for 2002, 2004 and 2005.

I consider that the previously is right, but I don´t understand why the DAS is not taking into account, which is so much or more toxic and aggressive than T-2 (Mirocha, 1979; Leeson et al, 1995; Gimeno, 2003; Gimeno and Martins, 2003; Gimeno and Martins, 2006) and supposedly more than HT-2.

Among T-2, DAS and HT-2, the one that has the highest LD50 is the HT-2 as previously shown.

With the showed data and the before comments, we have doubts if HT-2 toxin, will be or will not be important as undesirable substance in the animal feeding.

6.- BIBLIOGRAPHY

Gimeno, A. (2003). “Fusariomicotoxicosis comparativa entre pollos, gallinas, cerdos, vacas lecheras y conejos” en www.engormix.com (sección en español) (http://www.engormix.com/fusariomicotoxicosis_comparativa_entre_pollos_s_articulos_242_AVG.htm) (consultado 10-05-2010).  

Gimeno, A. y Martins, M.L. (2003). Micotoxinas de Fusarium en varias especies animales. Albeitar, 63. pp. 42-44.

Gimeno, A. and Martins, M.L. (2006). Mycotoxins and Mycotoxicosis in Animals and Humans. Special Nutrients, Inc. USA (Ed.). Victor Mireles Communications, Mexico City (Mexico). pp. 1-127.         
 
Leeson,S., Diaz,G.J and Summers, J.D. (1995). Poultry Metabolic Disorders and Mycotoxins. University Books (Ed.), P.O. Box 1326, Guelph, Ontario (Canada) N1H 6N8. pp.1-351.

Mirocha, C.J. (1979). "Trichotecene Toxins Produced by Fusarium" in Conference on Mycotoxins in Animal Feeds Grains Related to Animal Health. W.Shimoda (Ed.). PB-300 300. Food Drug Administration, Rockville,MD,June8, report FDA/BVM-79/139, pp.288-373.

Chi, M.S; Robison, T.S; Mirocha, C.J and Reddy, K.R. (1978). “Acute Toxicity os 12-13-Epoxytrichothecenes in One-Day-Old Broiler Chicks”. Applied and Environmental Microbiology. Vol.35, pp.636-640.

Weber, M; Balogh, K; Fodor, J; Erdélyi, M; Ancsin, Z; Mézes,M. (2010) “Effect of T-2 and HT-2 Toxin during the Growing Period on Body Weight,Lipid Peroxide and Glutathione Redox Status of Broiler Chickens”. ACTA VET. BRNO 2010, 79: 27–31; doi:10.2754/avb201079010027.

Official Journal of the European Union (2006). Commision Recommendation of 17 August 2006, on the presence of deoxynivalenol, zearalenone, ochratoxin A, T-2 and HT-2 and fumonisins in products intended for animal feeding. L229, 2006/576/EC, published 23-08-2006