Seven 6-day-old SPF piglets from one litter were inoculated intranasally with cell-free sonicated extract of Bordetella bronchiseptica four times every day for 64 days. Distilled water-inoculated and non-treated piglets were used as control animals. The cell-free sonicated extract was obtained from B. bronchiseptica strain L3, phase I, which contained a high level of heat-labile toxin. All the piglets were slaughtered for necropsy at 70 days of age. Various degrees of atrophy of the nasal turbinates in the maxillary sections were grossly observed in them. Lesions similar to those of swine atrophic rhinitis were found microscopically: rarefaction of the turbinate bone, degenerative changes of bone cells, proliferation of osteoblasts and osteoclasts, thickening of the periosteum, cell infiltration in the lamina pvropria, and hyperplasia of the nasal epithelium. Effects of the extract were also observed in other organs. The results suggest that the heat-labile toxin of B. bronchiseptica may be responsible for the development of atrophic rhinitis in the piglets.
