Acute airsacculitis in turkeys inoculated with Pasteurella multocida

Thirty female turkeys, inoculated into the caudal thoracic air sacs with Pasteurella multocida were examined from 0 to 6 hours post-inoculation (PI). The air sac reacted rapidly and intensely with exudation of heterophils. Circulating leukocyte and thrombocyte numbers remained normal except for an absolute lymphopenia by 6 hours PI. P. multocida was initially isolated from blood at 3 hours PI. Total cell counts increased markedly in air sac lavage fluids by 1.5 hours PI and continued to increase until 6 hours PI. Heterophils predominated in lavage fluids (greater than 94%), with macrophages comprising the remaining cells. Microscopically occasional heterophils were present within air sac blood vessels and perivascularly by 0.5 hour PI. They became more numerous by 1.5 and 3 hours PI when transepithelial migration into the air sac lumen was seen. By 6 hours PI, there was diffuse, severe swelling of air sac epithelium and mesothelium, and bacteria were located in air sac interstitium. Ultrastructurally, endothelial and air sac epithelial cells were swollen and vacuolated Interdigitating processes of air sac epithelial cells were separated. These results indicate that air sacs can be the portal of entry for P. multocida into the systemic circulation, probably via damaged air sac epithelium.