Rabbit pasteurellosis: respiratory and renal pathology of control and immunized rabbits after challenge with Pasteurella multocida.

Gross and microscopic lesions of pasteurellosis were studied in control and immunized pasteurella-free rabbits after challenge with virulent Pasteurella multocida. Pathologic responses were compared in rabbits immunized intravenously or mucosally with P. multocida or with J5, a cross protective core LPS mutant of E. coli. All rabbits were challenged conjunctivally with approximately 2xLD50 of P. multocida. Rabbits were necropsied and examined for histopathology of the respiratory tract and kidneys. Lung lesions varied in severity depending on the duration of the disease, the route of vaccination, and the vaccine used. The most severe lung lesions occurred in rabbits vaccinated intravenously with P. multocida and challenged with the same strain. Some of these rabbits had purulent bronchopneumonia and pleuropneumonia. Lung lesions were absent or less severe in rabbits vaccinated by a mucosal (aerosol, conjunctival) route and in unvaccinated controls. In these animals there was no bronchopneumonia or pleuropneumonia, and bronchiolitis, if present, was less severe. Kidney lesions were found only in rabbits vaccinated intravenously. There was an interstitial nephritis, some collagen deposition, mononuclear cell infiltration, and a loss of tubular architecture in the cortex. Some glomeruli were affected. These results indicate that intravenous immunization contributes to the formation of lesions whereas mucosal immunization prevented lesion formation to some degree.