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