Naturally acquired turbinate atrophy in rabbits was associated with Pasteurella multocida infection. Several in vitro and in vivo studies were conducted to document toxin production from P. multocida isolates and to determine the relation of toxin to atrophic rhinitis in rabbits. Ten isolates of P. multocida serotype A:12 were obtained from adult New Zealand White rabbits with noninduced atrophic rhinitis. Specific-pathogen-free rabbits inoculated intranasally with isolates of P. multocida developed rhinitis and turbinate atrophy. However, inoculation with filtrates of the same bacteria failed to induce turbinate atrophy. Cytotoxicity was observed in assays, using bovine embryonic turbinate cell cultures with extracts of P. multocida, but not in agar overlay cytotoxicity assays, using bovine embryonic turbinate, bovine embryonic lung, or Vero cell cultures, or in a sandwich ELISA, using monoclonal antibodies to purified P. multocida toxin. Thus, turbinate atrophy was experimentally reproduced in rabbits with isolates of P. multocida, but toxin was only detected in vitro by cell culture assay of P. multocida extracts.

Caseous lymphadenitis (CIA) caused by Corynebacterium pseudotuberculosis is a worldwide disease of sheep and goats and is characterized by development of pyogranulomas in lymph nodes and lungs. Control of this disease by vaccination remains controversial, although toxoid vaccines are now commercially available in some countries. To determine the efficacy of acquired immunity to control CLA, the effect of primary infection on subsequent challenge exposure was investigated. Adult seronegative ewes were primarily inoculated with a streptomycin-sensitive strain of C pseudotuberculosis on the external part of the left ear and thereafter challenge-exposed by inoculation of the streptomycin-resistant strain 19R in the right ear. This protocol indicated that primary infection with at least 10(7) viable bacteria induced strong protection against subsequent challenge exposure; the ewes with primary infection did not develop lesions as a result of challenge exposure, whereas immune-naive ewes developed numerous pyogranulomas in the right car, in lymph nodes draining the inoculation site, and in the lungs. However, ewes with primary infection remained carriers of the disease as a result of primary inoculation. These results offer experimental support for development of more effective vaccination to control CLA, in sheep and goats, and this model indicates that animals with primary infection can be used as positive controls for protection when testing a candidate vaccine against CLA.