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[[Image:Interstitial pneumonia micro.jpg|right|thumb|150px|<small><center>Interstitial pneumonia (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
*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 Virus|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 [[Pulmonary Emphysema|interstitial emphysema]]
Examples:
====Acute bovine pulmonary emphysema and oedema (ABPEE)====
[[Image:Fog fever 1.jpg|right|thumb|150px|<small><center>Fog fever (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
[[Image:Fog fever 2.jpg|right|thumb|150px|<small><center>Fog fever (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
[[Image:Tracheal haemorrhage in fog fever.jpg|right|thumb|150px|<small><center>Tracheal haemorrhages in fog fever (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
*Synonym: '''fog fever'''
*Usually seen in adult beef cattle in the autumn as an outbreak
*Associated with a change in pasture (from dry to lush, green)
*Severe respiratory distress with laboured breathing and grunting on expiration
*Can result in [[Diffuse Fibrosing Alveolitis|diffuse fibrosing alveolitis]]
*Gross appearance is that of enlarged wet lungs, the interlobular septa are markedly widenedith [[Pulmonary Oedema|oedema]] and [[Pulmonary Emphysema|emphysema]]
*Underlying pathogenesis is ingestion of L-tryptophan in the pasture which is metabolised to 3-methylindole -> bloodstream -> lungs -> metabolised into a compound toxic to Type 1 pneumonocytes and non-ciliated bronchiolar epithelium
*Their loss allows massive flooding of the alveoli with a protein-rich fluid
*The sequence of events in the lung is as follows:
**Alveolar flooding with a protein-rich fluid due to the necrosis of Type 1 epithelium
**As the incoming air dries this fluid, fibrinous 'hyaline membranes' form
**Proliferation of the more resistant cuboidal Type 2 epithelium which line the alveoli, called 'epithelialisation'
**Then either there is
***Digestion of the hyaline membranes by macrophages which when completed, allows some of the proliferated Type 2 epithelium to differentiate into Type 1 and reconstitute the functional respiratory unit - a normal alveolus
**Or
***Organisation of the fibrin into fibrous tissue in the lumen - destroying the alveolus or proliferation of fibrous tissue in the alveolar wall with retention of the epithelialised appearance to the alveolus
*Sequel
**Residual scarring if animal survives initial onslaught
**In chronic exposures there may be extensive fibroplasia
*Ingestion of sweet potatoes ifested with ''Fusarium solani'' mould or pasture contaminated with stinkweed or purple mint, rapeseed and kale also cause pulmonary oedema, emphysema and interstitial pneumonia
[[Image:Paraquat poisoning.jpg|right|thumb|150px|<small><center>Paraquat poisoning (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
====[[Paraquat Poisoning]]====
====Diffuse alveolitis====
[[Image:Diffuse fibrosing alveolitis.jpg|right|thumb|150px|<small><center>Diffuse fibrosing alveolitis (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
*Chronic disease of adult cattle occuring sporadically
*Probably caused by repeated subclinical incidents of fog fever or farmer's lung
*[[Extrinsic Allergic Bronchio-Alveolitis|'''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'''
[[Category:Pneumonia]]