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===Pathology===
 
===Pathology===
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A haemorrhagic gross pathology of BTV infection reflects the endothelial damage responsible for disease pathogenesis. Certain lesions have been describes as "pathognomic" for bluetongue: these include necrosis of the papillary muscle in the left ventricle, and haemorrhage in pulmonary arterial wall. However, these lesions may be difficult to visualise in mild or recovering cases and may occasionnally occur in other diseases such as pulpy kidney disease or Rift Valley fever.  
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A haemorrhagic gross pathology of BTV infection reflects the endothelial damage responsible for disease pathogenesis<sup>1</sup>. Certain lesions have been describes as "pathognomic" for bluetongue: these include necrosis of the papillary muscle in the left ventricle, and haemorrhage in pulmonary arterial wall. However, these lesions may be difficult to visualise in mild or recovering cases and may occasionnally occur in other diseases such as pulpy kidney disease or Rift Valley fever.
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In addition to these characteristic lesions, the oral mucosa is found to be hyperaemic and oedematous and occasionally cyanotic on post-mortem examination, and petechial or ecchymotic haemorrhages may be present. The ruminal pillars and omasal folds can also appear hyperaemic, and abrasions may be seen on the lips, dental pad, tongue and cheeks. These are sometimes covered by grey necrotic material. Moderate lymphomegaly and splenomegaly are apparent, and there are areas of necrosis in the skeletal musculature. Pulmonary oedema and catarrhal inflammation of the upper respiratory tract is seen in some cases.
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sheep the basic pathological process is endothelial damage. Haemorrhages,
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2–15 mm in diameter, in the tunica media at the base of the pulmonary artery are
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regarded as being characteristic of BT. The most prominent gross lesions in the
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gastrointestinal tract are found in and around the mouth. There is oedema and
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hyperaemia in the mucosa, which is occasionally cyanotic. Petechial or ecchymotic
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haemorrhages may also be present. Abrasions, which may be covered by grey necrotic
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material, are found on the lips, dental pad, tongue and cheeks. Hyperaemia of the
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ruminal pillars and reticular folds is common.
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The lymph nodes and spleen are moderately enlarged and haemorrhagic. Pale areas of
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necrosis are scattered through the skeletal musculature. There is inflammation of the
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upper respiratory tract causing excess mucus secretion (catarrhal inflammation), and
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oedema of the lungs may result from damaged alveolar epithelium.
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Microscopic lesions (histopathology)
   
6.10 Histologically, there is damage to the endothelium of small blood vessels. This
 
6.10 Histologically, there is damage to the endothelium of small blood vessels. This
 
results in vascular occlusion and clotting. In epithelial tissues this leads to lack of
 
results in vascular occlusion and clotting. In epithelial tissues this leads to lack of
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