Pneumonia in lambs inoculated with Bordetella parapertussis: clinical and pathological studies

Eight one-week-old, colostrum-deprived lambs were inoculated intratracheally with ovine isolates of Bordetella parapertussis. After inoculation, the lambs showed slight depression and anorexia. The total circulating leucocyte counts in these animals rose gradually to a peak five days post-inoculation. Neutrophil counts also increased and were highest at Day 3. Lesions grossly and histologically similar to those of naturally-occurring ovine chronic non-progressive pneumonia were seen in the majority of infected animals. Grossly, they consisted of many small areas of collapse and dull-red consolidation. Histologically, B. parapertussis caused mild acute tracheobronchitis, severe alveolar collapse and acute bronchopneumonia, which was most severe from Days 1 to 3. Pure cultures of B. parapertussis were consistently recovered from nasal swabs of infected lambs throughout the study. Viable bacterial counts of bronchoalveolar lavage fluid showed a rapid elimination of this organism from the lower respiratory tract between Days 1 to 5. Bordetella parapertussis infection in the respiratory tract of lambs has the potential to compromise pulmonary defence mechanisms and allow other pathogenic organisms to become established in the lower respiratory tract.