Module 4: Occupational Allergy - Lecture

1. DEFINITION: OCCUPATIONAL ALLERGY:

• Diseases resulting from a hypersensitivity (exaggerated response) of the immune system to substances encountered in the work environment.
• Constitute 15% of all occupational diseases (Finland)
• Features:
  • initial contact with antigen;
  • latent sensitisation period of weeks to years between first exposure and development of symptoms;
  • temporal symptoms on exposure to very low doses of allergen;
  • (exposure to non-specific irritants may trigger a reaction).

2. ALLERGENS:

These are proteins (animal, plant, microbial), enzymes (synthetic), chemicals, spices. These proteins are usually of high molecular weight and cross-react.

3. ROUTES OF EXPOSURE:

• airborne;
• dermal contact;
• (possible) ocular;
• ingestion (cross-reactivity).

4. FACTORS INFLUENCING MANIFESTATION OF ALLERGIC DISEASES:

• dose, duration and route of exposure;
• physical and chemical properties of agent;
• allergenic potency;
• industrial hygiene and engineering practices;
• host factors: atopy, smoking, non-specific bronchial hyper-responsiveness, HLA type.

The diagram below depicts the natural history of an allergic disease such as occupational asthma, illustrating the contribution of these various factors.

5. IMMUNOLOGICAL MECHANISMS:

Coombs and Gell defined four types of immune hypersensitivity reactions:

• Type I - immediate hypersensitivity reaction (IgE-mediated release of inflammatory mediators such histamine) (Figure below) e.g. flour dust causing asthma among bakery workers.

  

• Type II - cytotoxic reactions (IgG or IgM antibodies against cellular/tissue antigens) e.g. trimellitic anhydride (TMA) causing pulmonary disease anemia syndrome among chemical workers.
• Type III - immune complexes reaction (circulating Ag/Ab complex deposition in capillaries and activating the complement cascade) e.g. pigeon droppings causing extrinsic allergic alveolitis among pigeon breeders.
• Type IV - delayed cell mediated reaction (cytotoxic T cells activation): e.g chrome in cement causing allergic contact dermatitis among builders.