Abnormalities (lesions) are generally confined to the chest cavity (Plate 2) except in young calves, where inflammation of the limb joints (usually the carpal and tarsal joints), with increased fluid, is sometimes seen (Plate 3).
A most striking feature of the acute disease is the very large volume of yellow fluid (up to 30 litres) containing clots, which can accumulate in the chest (Plate 4).
The lungs (almost always one) and pleura are affected. In most cases, only the diaphragmatic lobe is involved (Plate 5); it is firm and fleshy, resembling liver rather than healthy pink lung. It does not collapse when the chest is opened.
In acute forms, the yellowish fluid in the chest cavity may solidify and cover the lining of the chest and surface of the lung (the pleura) with a yellow or yellowish-grey coating resembling an omelette (fibrin) (Plate 6). Under this, the pleura is thickened and opaque. Accumulation of fibrin on the pleura causes the lung and chest wall to stick together (adhesion). The cut surface of the lung often shows a marbled appearance, with areas of different colour (dark red, red and pale pink) separated by a network of pale bands (Plates 7 and 8); this is typical of CBPP.
In the chronic form, fluid is rarely seen in the pleural cavity, but adhesions between lung lobes and between lungs and the chest wall are commonly found. A capsule of fibrous connective tissue surrounds areas of dead lung tissue. This structure is called a sequestrum [plural: sequestra] (Plate 9). Various intermediate stages between the acute lesion and a fully formed sequestrum can be found, depending on the stage of the disease. The diameter of a sequestrum can vary from 2 to 25 cm and the capsule can be as much as 1 cm thick. Sequestra of different diameter can be detected in the same lung. When they are small and deep they can be felt only by careful palpation.
In the pink or white necrotic - odourless - mass that is found in the sequestrum, the lobular structure of the lung may still be recognizable. This is typical of the disease and differs from lung lesions due to tuberculosis or abscesses. The contents of sequestra shrink, and become dry, although they may later become liquefied.
Lymph nodes in the chest may be enlarged and wet (oedematous), with small necrotic foci and pinpoint haemorrhages. The difference between cortex and medulla may be indistinguishable. In the kidney cortex, white spots of dead tissue of variable size, called infarcts, can sometimes be seen (Plate 10).
In summary, look for:
Slaughterhouse monitoring is a powerful tool to use in detecting introduction and spread of the disease because the lesions of CBPP are so characteristic.