Pathology | Blackleg

The hind limbs are markedly swollen with severe, diffuse subcutaneous edema and a yellow gelatinous fluid. The thigh musculature contains multifocal hemorrhage and emphysema, surrounded by normal muscle tissue. This pattern may be observed in  superficial and deep muscles of the limbs. Linear hemorrhages are commonly seen within the affected muscles. Histopathology of skeletal muscle from the limbs reveal severe, diffuse necrosis and inflammation. Muscle fascicles are often separated by large areas of emphysema and edema that can be seen in adjacent myofibrils. Large numbers of neutrophils can be found around necrotic fibers or between fasciculi. Swollen, hyalinized myofibrils with disrupted sarcolemma and granular sarcoplasm were sometimes observed.

Myocardial congestion and interstitial hemorrhage is seen with large volumes of blood-stained pericardial fluid. The pericardial fluid usually contains fibrin.

Histological examination of heart reveals large, multifocal, locally-extensive areas of acute coagulative myocardial necrosis . The affected area may contain moderate numbers of Gram-positive bacterial rods, consistent with Clostridium spp. These areas with the bacteria may be associated with considerable interstitial congestion, edema and hemorrhage. Occasionally interstitial vessels contain cellular fibrin thrombi. Fibrinous, fibrinopurulent or fibrinohemorrhagic epicarditis, mostly of diffuse distribution, can be evident.

Renal congestion and edema are seen less frequently. Hemorrhage and bruising are observed adjacent to docking wounds.