General Introduction

In the poultry industry, mycotoxins and mycoplasma are among the most critical pathogens directly and indirectly affecting avian health and productivity. Both can induce immunosuppression, rendering birds more susceptible to secondary diseases, reducing vaccine efficacy, and impairing the biological ability to resist infection.

I. Mycotoxins

What are Mycotoxins?

Mycotoxins are toxic secondary metabolites produced by specific types of fungi that proliferate on crops and feed under certain environmental conditions (high humidity and improper temperatures). These toxins are prevalent in corn, soybeans, and other cereal grains used in poultry feed formulation.

Common Types of Mycotoxins in Poultry

The most significant toxins facing poultry production include:

• Aflatoxins
• Ochratoxins
• Trichothecenes (e.g., DON/Vomitoxin)
• Fumonisins

These toxins differ in their toxicological mechanisms and their degree of impact on the liver, kidneys, and the immune system.

Clinical Signs in Birds Exposed to Mycotoxins

Birds consuming contaminated feed exhibit various clinical signs depending on the toxin type and concentration:

• Reduced growth rate and impaired Feed Conversion Ratio (FCR).
• Decreased egg production and lower final body weight.
• Hepatic (liver) and renal (kidney)
• Gastrointestinal disorders.
• Immunosuppression via multiple mechanisms without these toxins acting as antigens that directly stimulate an immune response.

How Mycotoxins Affect the Immune System

1. Suppression of Humoral and Cell-Mediated Immunity: Toxins like Aflatoxin B1​ and DON inhibit lymphocyte proliferation and impair immune cell functionality, leading to reduced antibody production and diminished response to vaccination or natural challenges.
2. Impact on Primary Lymphoid Organs: Mycotoxins cause atrophy of the Bursa of Fabricius, the thymus, and damage to the spleen—the central hubs of the avian immune system.
3. Impaired Vaccine Response: Numerous studies have demonstrated that birds fed contaminated diets show lower antibody titers following vaccination against common diseases such as Newcastle Disease (ND) and Infectious Bursal Disease (IBD).
4. Increased Susceptibility to Co-infections: Immunological dysfunction leaves birds vulnerable to exacerbated pathology when exposed to other pathogens like coli, Coccidiosis, and respiratory viruses, leading to complex polymicrobial syndromes.

Mechanisms of Mycotoxin-Induced Immunosuppression

• Protein Synthesis Inhibition: Toxins bind to ribosomes, halting the synthesis of proteins essential for immune cell functions.
• Apoptosis: Induction of programmed cell death in immune cells, reducing the population of functional leukocytes.
• Oxidative Stress: Induction of chronic inflammation and oxidative damage that disrupts immune cell localization and signaling.

II. Mycoplasma in Poultry

What is Mycoplasma?

Mycoplasma are very small bacteria lacking a cell wall. They are primary agents of respiratory diseases in poultry, most notably Avian Mycoplasmosis caused by Mycoplasma gallisepticum (MG).

This bacterium causes chronic respiratory inflammation characterized by:

• Sneezing, coughing, and nasal discharge (coryza).
• Infraorbital sinus swelling (swollen face/eyes).
• Decreased production and weight gain.
• Infected birds remain lifelong carriers and shedders of the microbe.

How Mycoplasma Affects Immunity

Mycoplasma induces immunological disturbances through several mechanisms:

1. Damage to Lymphoid Organs: Recent research indicates that MG causes direct injury to the Bursa of Fabricius, thymus, and spleen, leading to lymphopenia and tissue degradation of key immune organs.
2. Oxidative Stress and Apoptosis: Infection triggers oxidative stress and promotes apoptosis in host tissues, weakening immune defenses.
3. Interference with Immune Cell Distribution: The pathogen manipulates immune signaling, disrupting the trafficking and proliferation of CD8+ and CD4+ cells within lymphoid tissues, thereby weakening the overall response.

Mycoplasma and Mediated Immunosuppression

While Mycoplasma does not suppress immunity in the exact same manner as mycotoxins, it leads to:

• Depletion of local immune resources in the respiratory tract.
• Cytokine imbalance.
• Weakened immune response following a pathogenic challenge.

Studies show that MG-infected birds respond poorly to vaccines, including Mycoplasma vaccines themselves or other opportunistic challenges.

Interaction Between Mycotoxins and Mycoplasma

When a bird is simultaneously exposed to both factors:

• Immunosuppression is significantly exacerbated.
• The immune response to other diseases is severely diminished.
• Vaccination failure becomes highly prevalent.
• Increased mortality rates and a sharp decline in production.

This synergy complicates disease pathology, making diagnosis and treatment far more difficult.

Conclusions and Practical Recommendations

• Prevention is Better than Cure:
  • Routine screening and analysis of feed for mycotoxins.
  • Optimizing feed storage by controlling humidity and temperature.
  • Enhancing biosecurity and hygiene to reduce environmental contamination.
• Boosting Innate Immunity:
  • Providing balanced nutrition supplemented with vitamins and immunomodulators.
  • Continuous monitoring for early detection of infection or physiological weakness.
• Effective Vaccination Programs:
  • Adjusting vaccination schedules during periods of stress or high disease pressure.
  • Utilizing appropriate vaccines while monitoring serological antibody titers.

Summary