Interstitial Pneumonia

Interstitial pneumonia (Image sourced from Bristol Biomed Image Archive with permission)

• Lung inflammation that occurs primarily in alveolar walls rather than in alveolar spaces
• Can be widely distributed but is often most severe in caudal lung lobes
• Diffuse or patchy damage to alveolar septa, may be acute or chronic
• Lesions in most cases result from blood-borne insult and are more likely to involve the dorsocaudal regions, although the damage is often diffuse
• No concentrated inflammatory response in the airway, only secondary to damage of alveolar walls
• As part of systemic infection
  • Canine distemper (in alveolar macrophages as inclusions)
  • Salmonellosis
  • Toxoplasmosis (in alveolar wall)

• Acute interstitial pneumonia is characterised by exudation into the alveolar lumen and in cattle is associated with interstitial emphysema

Examples:

Diffuse alveolitis

Diffuse fibrosing alveolitis (Image sourced from Bristol Biomed Image Archive with permission)

• Chronic disease of adult cattle occuring sporadically
• Probably caused by repeated subclinical incidents of fog fever or farmer's lung
• Farmer's Lung
  • Extrinsic allergic alveolitis
  • Hypersensitivity of ingested or inhaled moulds
  • May occur as an outbreak or sporadically in adult cattle

• Hypersensitivity diseases often cause an lymphocytic interstitial pneumonia
• Chronic interstitial pneumonia progresses to fibrosis
  • Sometimes called pneumonitis