Acute airsacculitis in turkeys inoculated with cell-free culture filtrate of Pasteurella multocida

Twenty-six female and 26 male turkeys, inoculated into the caudal thoracic air sacs with cell-free culture filtrate of Pasteurella multocida strain R44/6, were examined from 0 to 6 hours post-inoculation and compared with 26 female and 26 male sham-inoculated control turkeys given brain-heart-infusion broth. The air sac reacted rapidly with exudation of heterophils. Microscopically, low numbers of heterophils were present within air sac blood vessels and also perivascularly by 0.5 hour after inoculation. These became more numerous by 1.5 and 3 hours post-inoculation. By 6 hours post-inoculation, there was severe swelling of air sac epithelial and mesothelial cells and thickening of the air sac by proteinaceous fluid and heterophils. Ultrastructurally, mesothelial and air sac epithelial cells were vacuolated, and interdigitating processes of epithelial cells were separated. Microscopically, in control turkeys, rare heterophils were present perivascularly at 1.5, 3, and 6 hours after inoculation. Ultrastructurally, all features were normal. In turkeys given cell-free culture filtrate, total cell counts in air sac lavage fluids increased markedly by 3 hours post-inoculation in which heterophils predominated (greater than 97%). There were only slight increases in cell counts of air sac lavages from control turkeys. The circulating blood heterophil cell count dropped transiently at 1.5 hours post-inoculation, followed by a return to normal 3 hours after inoculation, and by heterophilia by 6 hours post-inoculation in turkeys given either cell-free culture filtrate or brain-heart-infusion broth. These results indicate cell-free culture filtrate of P. multocida induces hematologic, cytologic, and morphologic changes indistinguishable from those induced by cultures of P. multocida.