EXPERIMENTAL-MODEL OF SWINE PNEUMONIC PASTEURELLOSIS USING CRUDE ACTINOBACILLUS-PLEUROPNEUMONIAE CYTOTOXIN AND PASTEURELLA-MULTOCIDA GIVEN ENDOBRONCHIALLY

This study was designed to develop and characterize a swine pneumonic pasteurellosis model by concurrent introduction of Pasteurella multoci da type A and Actinobacillus pleuropneumoniae crude cytotoxin. After a series of preliminary experiments, a combination of 4 x 10(9) P. mult ocida and 4,000 toxic units of A. pleuropneumoniae crude cytotoxin was determined to produce optimal results. A total of 48 pigs were divide d into four groups of 12 pigs each. The control group received buffere d saline only. Four pigs from each group were randomly selected for ne cropsy 3, 7 and 14 days postinoculation (PI). Inoculation of pigs with P. multocida and A. pleuropneumoniae cytotoxin (group 1) resulted in moderate to severe pneumonia. Pasteurella multocida was isolated from pneumonic lesions, grossly normal lung, and bronchial lymph nodes of a ll group 1 pigs throughout the 14 day experimental period. Pathologica l changes typical of field cases of swine pneumonic pasteurellosis wer e produced. Pigs inoculated with P. multocida alone (group 2) had pneu monic lesions and P. multocida was reisolated from lungs at three days PI. Pasteurella multocida was not isolated from these pigs at 7 and 1 4 days PI, except for one pig in which an abscess developed in the tho rax. Pulmonary lesions induced by A. pleuropneumoniae crude cytotoxin alone (group 3) were transient and resolved by seven days PI. Group 1 pigs had significantly greater lung lesion volumes than group 2 and 3 pigs at 3, 7 and 14 days PI. Statistical analysis indicated a signific ant interactive effect of P. multocida and A. pleuropneumoniae cytotox in on the development of lung lesion volumes at 7 and 14 days PI (p < 0.05). This suggests that there is an additive or synergistic interact ion between P. multocida and cytotoxin that is best demonstrated exper imentally at 7 to 14 days after challenge.