The contamination of feedstuffs with mycotoxins poses a serious threat to the health and productivity of livestock and poultry. The toxicological effects of mycotoxins are very diverse as they do not belong to a single class of chemical compounds.

Unfortunately, low level contamination can elicit sub-clinical effects that are often not apparent, but they can reduce the overall performance and productivity of those animals, eventually resulting in high economic losses for producers. The biological system where the subclinical effects of mycotoxins are most notable is the immune system.

The immune system is affected by many types of mycotoxins including aflatoxins, trichothecenes, fumonisins and ochratoxin A. All of these toxic compounds have been shown to suppress the immune system, decrease the animals’ resistance to environmental and microbial stressors and make them more vulnerable to diseases.

The primary function of the gastrointestinal tract is to digest and absorb nutrients in order to meet metabolic demands for maintenance, growth, and development. It also acts as a vital barrier preventing the entry of several potentially harmful pathogens from the external environment. Considering the fact that 70% of the immune system resides in the gastrointestinal tract, great care must be taken to protect it from threats such as mycotoxins. Furthermore, due to their ability to inhibit protein synthesis, mycotoxins and their metabolites specifically target areas with rapidly dividing cells and high levels of protein turnover, which are commonplace in the gastrointestinal tract whether it be the epithelial cells that line the intestinal tract or the immune cells that reside in the underlying lamina propria. Mycotoxins can also target other tissues with high cellular proliferation such as the lymphoid organs, which include the thymus and bone marrow (bursa of Fabricius in poultry) where T and B cells develop and mature, respectively. As these cells are important components of the immune system, any damage to these tissues can lead to substantial immunosuppressive effects and enhanced susceptibility to subsequent diseases.

Negative impacts of various mycotoxins

Aflatoxins are considered to be the most potent in terms of their immunosuppressive effects. It predominantly exerts its effects by binding to both DNA and RNA, blocking transcription, and thus inhibiting protein synthesis. The main immunosuppressive effects of aflatoxins are:

• Suppressed antibody production
• Reduced complement activity
• Impaired proliferation and altered production of cytokines by T-cells
• Depressed macrophage effector cell function

Over 180 trichothecenes have been identified so far and most of them inhibit protein synthesis by binding to eukaryotic ribosomes. The main immunosuppressive effects of trichothecenes are:

• Reduced proliferation and activity of B- and T-cellsSuppressed antibody production
•  Depressed macrophage effector cell function
• Decreased mucus production
• Weakened intestinal cell tight junctions

Fumonisins disrupt sphingolipid metabolism and block the synthesis of complex sphingolipids from sphinganine (Sa) and sphingosine (So). As a consequence, Sa and So accumulate in tissues and inhibit many cellular activities. The main immunosuppressive effects of fumonisins are:

• Reduced antibody response
• Impaired efficacy of vaccines
• Reduced macrophage numbers and effector cell function
• Decreased lymphocyte count and activity

Ochratoxins act by inhibiting the translation portion of protein synthesis by blocking phenylalanine tRNA synthetase. The main immunosuppressive effects of ochratoxins include:

• Cellular depletion of lymphoid organs
• Reduced antibody production
• Suppressed macrophage and heterophil effector cell activities

It is important to realize that the effects of mycotoxins on the immune system may severely impact the health status of the entire farm by not only increasing the susceptibility of the animals to disease, but also by lowering the efficacy of vaccination programs. Combatting mycotoxins in the feed will undoubtedly be more cost effective than dealing with the aftermath of these toxins. Therefore, an effective mycotoxin counteracting strategy must be implemented to protect animal health and profit margins.