Outbreak of swollen head syndrome and cranial cancellous bone lesions caused by Pasteurella multocida in chickens

摘要

Between August 1994 and February 1997, swollen head syndrome was discovered on one layer chicken and three broiler chicken farms in western Japan. Mortality ranged from 3.6% to 12.3%. The disease occurred among fowls aged 36 to 195 days. Clinical signs were characterized by depression, swollen heads and torticollis. At necropsy, the most noticeable lesion was yellowish, caseous material in the air cavity of the cranial bone. Edema and caseous exudate were also observed in the facial subcutis of certain chickens. Microscopically, severe periostitis and purulent inflammation of the air spaces of the calvarial cancellous bone were present in all chickens. Cellulitis and encephalomeningitis were detected less frequently. Inflammation of the air spaces extended through most of the spongy bone. Early lesions affecting the lining membrane were seen as flooding of the lacunae with proteinaceous fluid and migration of heterophils through the epithelium into this fluid. As cellular infiltration increased, purulent foci become necrotic and stimulated a marked peripheral giant cell response. Clusters of Gramnagative bacteria were observed in the lesions. In some of the fowls, extension of the lesions from pneumatic spaces of calvarial cancellous bones resulted in the establishment of severe purulent encephalomeningitis. Pasteullera multocida was isolated purely from all the affected calvarial cancellous bones. The isolates were identified as Carter's capsuler type A and Heddleston's somatic type 3.4.