Extrinsic Allergic Bronchio-Alveolitis

• 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