Extrinsic Allergic Bronchio-Alveolitis

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  • Synonym: Bovine Farmers Lung
  • Arises due to repeated inhalation of spores of thermophilic actinomycetes in mouldy hay (Micropolyspora faeni and Thermactinomyces vulgaris)
  • Can be experimentally reproduced by repeated exposure to M. faeni aerosols
  • Disease primarily of housed animals in winter
  • Spores can penetrate to the level of terminal bronchioles and alveoli throughout the lung
  • Pathogenesis results from a type III (Arthus) hypersensitivity reaction to the inhaled fungal spores
  • Macroscopically:
    • Lungs appear normal however on close inspection, numerous small grey nodules representing lymphoid reaction are evident
  • Histologically:
    • Lymphocytic/plasmacytic bronchitis/ bronchiolitis
    • Associated thickening of the alveolar septae
    • In severe and chronic disease, the lesions can progress to severe interstitial fibrosis and type II hyperplasia
    • In extreme cases, vascular compromise may -> pulmonary hypertension -> cor pulmonale