Systematic Veterinary Virology

LESIONS

• The lesions of BT in sheep vary greatly depending on
• the strain of virus, 
• individual animal and breed susceptibility and
• environmental (stress) factors. Prominent lesions include facial edema, edematous ears, and dry, crusty exudate over the nostrils.
• Oral cavity and digestive system: Lesions in the oral cavity include focal petechial hemorrhages that progress to gray necrotized debris over erosions and ulcerations on the lips; on the dorsal, lateral, and ventral surfaces of the tongue; and on the dental pad. The buccal mucosa may be cyanotic. Hyperemia and occasional erosions can occur on papillae and laminae in the reticulum and omasum. 
• Respiratory System: Lesions include cyanosis and edema of the nasal mucosa and pharynx. 
• Vascular system: Lesions include hyperemia, edema, and hemorrhages. A characteristic lesion is hemorrhage at the base of the pulmonary artery. Petechial and ecchymotic (larger than pinhead-size) hemorrhages may be observed at times in the endocardium. Focal gray-white areas of necrosis are often found in the papillary muscles and less frequently in other areas of the myocardium
• Skin: Dermal and subcutaneous edema of the head and ears and an irregular rash (exanthematous eruptions) with serous and crusty exudates on the skin are the common lesions.
• Muscle: A yellow gelatinous exudate is present in the fascia (connective tissue) along and between skeletal muscles. On the cut surface of the heavy muscle there may be focal hemorrhages and areas that appear dry and gray-white.
• Newborn lambs: Newborn lambs with congenital BT have hydranencephaly or porencephaly. Abnormal development of cerebellum and spinal cord are the other lesions.