The characteristic lesion is Blue wing disease wherein the focal lesions (mostly in the wings) appear as ecchymotic skin haemorrhages, which may turn blue and may break, releasing serosanguineous exudate which is prone to secondary bacterial infections, leading to gangrenous dermatitis. The mortality peaks 5 -6 days after the appearance of the
Clinical signs, declining to normal 5 – 6 days later.
Thymus and bone marrow atrophy are the other lesions.