*Caused by [[Mannheimia haemolytica|''Pasteurella (Manheimia) haemolytica'']], possibly together with [[:Category:Mycoplasmas|''Mycoplasma ovipneumoniae'']]
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*Mainly in late spring/early summer after environmental stress i.e. handling or moving
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*May be acute with producing a fibrinonecrotic [[Bronchi and Bronchioles Inflammatory - Pathology#Infectious causes of bronchitis or bronchiolitis|broncho]][[Lungs Inflammatory - Pathology#Infectious causes of pneumonia|pneumonia]] and associated [[Pleural Cavity & Membranes Inflammatory - Pathology|pleuritis]]
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*Or tending towards chronicity with abscessation and fibrous pleural adhesions
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*A septicaemic form (mortality 5%) is reported to follow the stress of movement to new pasture in the autumn in weaned lambs.
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*Foci of necrosis containing many bacteria are seen at the site of initial invasion in the pharynx and in the '''[[Liver - Anatomy & Physiology|liver]]'''
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*Meningitis in young lambs and mastitis in ewes are other expressions