Harmful effect of mycotoxins on normal physiology

Harmful effect of mycotoxins on normal physiology

Low levels of mycotoxins have a significant negative metabolic and physiological impact on livestock animals.

Almost every agricultural commodity is affected through mould and mycotoxins. They are present in field as well as after harvesting in the stored feed.

Figure 1 Field fungus in pre harvested corn. Figure 2 Normal healthy corn apparently without any mycotoxin but might have field toxins which remain with the corns during its whole supply chain

Fungus grow on plants produces mycotoxins. These mycotoxins are harmful to plants itself. Plants evolved a novel method to protect themselves from these mycotoxins by conjugating them with some compounds. This process of temporary loss of toxicity of mycotoxins by binding them with other molecules (glucose, sulpher etc) is called MASKING of mycotoxins. These masked mycotoxins are polar in nature.

These metabolites are stored in plant vacuoles or conjugated to structures such as cell wall components.

Masked mycotoxins cannot be detected by conventional analytical methods like HPLC & ELISA due to changed molecular structure. When these masked mycotoxins are ingested intestinal enzymes cleaved them and the parent mycotoxins are released. These mycotoxins are absorbed into the blood and become again toxicto the animal.

Typical examples of such called “masked mycotoxins” are Zen4G as derivative from Zearalenone, DON 3G and DON 4G as masked forms of Deoxynivalenol, Ochratoxin α as conjugate of Ochratoxin A and many more derivatives have been identified over the last few years. In 2011, Berthiller was able to demonstrate that 62% of the DON 3G in a diet is transformed back into DON by the microbial population in the large intestine. It would be unwise to ignore this additional and large range of toxins.

Intestinal integrity may be challenged when exposed to mycotoxins (DON & Fuminosins B1)

The intestinal tract is the first barrier against ingested antigens, including mycotoxins and pathogenic bacteria.

Enterocytes are exposed to mycotoxins

(Tight junction maintains integrity of intestine)

Increase in level of cytokines (TNF- α and IL-1β)

Increase cytokines lowers down the gene expression of

tight junction proteins – such as occludin and E-cadherin

This decreases TEER (Trans Epithelial Electrical Resistance)

Compromised intestinal integrity

Intestinal cell lines, pretreated with non-toxic levels of DON, showed an increased invasiveness of S. typhimurium and an increased translocation through the cell layer.

Within an intestinal loop model, it has been demonstrated that simultaneous exposure of the intestinal tract by non-cytotoxic concentrations of DON and S. typhimurium resulted in an increased inflammation, which was not observed when exposed to only DON or S. typhimurium.

This means that together DON & Salmonella typhimurium have synergistic effects.

At low concentrations of DON, an enhanced uptake of S. Typhimurium by the macrophages.

It is well known that Salmonella can shelter and multiply in macrophages while being spread throughout the body.

Antonissen et al. (2012) challenged broiler chickens with Clostridium perfringens, being fed a control diet or a diet contaminated with DON (< 5000 ppb). Chickens that received DON had significantly more lesions (46.6%) as compared to the group challenged by C. perfringens without DON-exposure (19.5%). Within the current philosophy of disease prevention, mycotoxin control should become part of the basic strategy. Mycosis And Mycotoxicoses Mycosis And Mycotoxicoses Mycosis (Brooder’s Pneumonia) Causative agent – Aspergillus species Warm and humid environment is ideal for the growth of the fungus. Route – air borne infection. Moist litter and improperly stored grains are the major source of contamination. Predisposing factors include poor nutrition and unhygienic conditions. Signs Chicks of young age are commonly affected. Third to fourth week chicks commonly show signs of gasping. Increased thirst with gasping. Birds show stuhted growth, poor feathering and lethargy. The mortality ranges from 5 to 25% Lesions In acute cases fungal growth is seen in Lung. Peritonium. Thoracic airsacs. Abdominal airsacs. Soft muscles of the abdomen. Kidneys. Intestines. In Chronic cases nodules are seen in Lungs. Kidneys. Abdominal muscles. Liver – Histologically shows fatty to degenerative changes depending on the level of toxins, produced by the fungus. Diagnosis By gross lesions. Isolation of the fungus on Sabouraud’s agar. Mycotoxins The common mycotoxins affecting poultry are Aflatoxins Ochratoxins Trichothecenes Zearalenone and Citrinins Aflatoxins Prevalent, highly toxic and carcinogenic. Produced by Aspergillus flavus and A. parasiticus. The major groups are B1, B2, G1 and G2. B1 is produced in ground nut, corn, cotton seeds and various other cereals. Predisposing factors include drought, insect damage, delayed harvest, improper storage conditions of grains and hot and humid weather. Signs High level of toxins – causes sudden mortality without any symptoms. Low level of toxins – causes improper growth, impaired feed conversion, immunosuppression and signs of malnutrition. Loss of pigmentation and undigested feed particles in faeces. Young birds are more susceptible than adults. Drop in feed consumption is significant factor. Diarrhoea is also common. Lesions Liver enlarged pale and bleeds in acute cases. Degenerative changes in liver are present at low levels of toxin. Chronic cases – atrophy of liver with distended gall bladder. Spleen is also enlarged. Duodenum distended with catarrhal contents. Kidneys – swollen, congested with degenerative changes and haemorrhages. Haemorrhages are also seen in pancreas, subcutaneous portion of legs, and breast muscles. Hydropericardium and ascitis are common feature. Histopathology ACUTE Liver – swollen hepatocytes with homogenous cytoplasm, vacuolation and haemorrhages. In acute cases – liver shows haemorrhages, vacuolation, enlarged nuclei and spherical nucleoli. Liver-extensive fatty changes with irregular zone of hepatocytes are seen Chronic Cases Liver-fibrosis with extensive necrosis. Kidney – proximal tubular and collecting duct epithelium contain hyaline casts, intertubular haemorrhages and degenerative changes. ) Aflatoxins are immunosuppressive and causes atrophy of bursa of fabricius, thymus and spleen. Increases susceptibility to coccidiosis, marek’s disease, Salmonellosis, fowl cholera and other diseases. Ochratoxins Highly toxic mycotoxins produced by Penicillium viridicatum and A. ochraceous Out of different types of ochratoxins, the important and toxic to poultry are ochratoxin-A,B, C and methyl ester. Ochratoxin-A Is most common, highly toxic and thermostable. Signs Similar to aflatoxins in chronic cases. Reduced renal functionwithout any gross lesions. Lesions Liver shows pale discolouration. Enteritis is common. Kidney is pale, shows nephrosis with swelling of tubular epithelial cells, tubular dilation and proteinaceous material in the lumen in acute cases. Kidneys show marked accumulation of urates in the ureters. Occasionallyurate deposits are also seen on visceral organs. Weights of liver and kidney increases and weights of lymphoid organs decreases in subacute toxicity. Histopathology kidney The changes are acute nephrosis characterized by proteinaceous urate casts. Extensive necrosis of the glomeruli and tubules. Nephrosis and heterophil infilitration with areas of focal necrosis. Tubular casts, tubular aliatation, and hyperplasia of tubular epithelium is common in subacute cases. Liver Cytoplasmic vacuolation, focal necrosis and infiltration of polymorphs. Parenchyma develops cytoplasmic vacuolation and focal necrosis of hepatocytes with little infiltration of polymorphs. Ochratoxin A is immunosuppressive. It chiefly causes thymic atrophy and impairs cell mediated and humoral immunity Trichothecenes Produced by Fusarium Calonectria and Gibberella species. Those toxic to poultry are T2, DAS, DON and Nvalenol Symptoms and Lesions Reduced growth and marked depression. Bloody diarrhea. Necrosis of oral mucosa is the most common and important sign. Oral lesions are white to creamy raised ulcers on the borders of the tongue and inside borders of upper and lower beak. Necropsy shows reddening of the gastrointestinal mucosa. Mottling of liver and distended gall bladder. Atrophy of spleen and visceral haemorrhages are common. Histopathology Mucosal necrosis submucosal granulation and inflammatory cells are seen. Liver, with necrosis of hepatocytes accompanied by haemorrhages. Proliferation of bile duct epithelium. There is no evidence of immunosuppression in chickens. Zearalenones Oestrogenic in activity and produced by Fusarium graminarum and F. roseum. There are 7 derivatives of this group, but zearalenone and zearalenol are toxic to poultry. Zearalenone grows well in corn and sorghum. Show adverse effect in broiler breeders in the form of reduced egg production, but no effect on fertility and hatchability. The most common symptom is ascitis. Oviduct is distended with cysts and fibrinous material. Histopathological findings in the oviduct and peritoneum are caseous cysts accompanied by chronic inflammation. Citrinins Produced by penicillium citrinum and other species of Penicillium which are nephrotoxic. Affected birds consume large quantities of water and show diarrhea. Withdrawal of infested feed results in normalcy within 8 to 10 hrs. Lesions Except enlargement of kidneys, no other lesion is evident. Histopathological changes in liver show multifocal necrosis of hepatocytes accompanied by haemorrhages. Necrosis and depletion of lymphoid tissues is a common feature in acute citrinin toxicosis. Citrinin has no effect on either humoral or cell mediated immunity in broilers.