Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/1996
Publication Date: N/A
Interpretive Summary: Toxigenic strains of Pasteurella multocida are associated with atrophic rhinitis. Experimentally purified P. multocida toxin induces changes in pigs similar to that seen in clinical cases of atrophic rhinitis. These changes include: nasal deformities, decreased weight gain, and a small body stature. This study demonstrates that the toxin reduces growth of long bones of pigs. More specifically, the toxin reduces proliferation of cells within the growth plates of long bones. In addition, this effect of toxin on the long bones can be prevented by hyperimmune serum (containing) antibodies to toxin). Thus, this study shows that small stature and decreased weight gain seen in pigs with atrophic rhinitis may be due to an affect of the toxin on the growth of long bones. Hyperimmune serum prevents this effect and indicates that proper vaccination may prevent detrimental effects of P. multocida toxin in pigs.
Technical Abstract: P. multocida toxin (PMT) reduces conchal bone formation and weight gain in growing pigs. In this study, twenty colostrum-deprived, Caesarean-derived pigs were divided into five groups (n=4/group) in order to determine the effect of PMT on chondrocytes of the proximal growth plate of the humerus (endochondral bone formation). Group 1 received 0.1 cc PBS for 4 weeks; Group 2: 0.05 ug/kg PMT at 14 and 21 days; Group 3: 0.05 ug/kg PMT at 28 and 35 days; Group 4: PMT 0.1 ug/kg at 14 and 21 days; and Group 5: hyperimmune serum (from a sow given purified toxin) on days 13, 20, 27, and 34 and 0.1 ug/kg PMT on days 14, 21, 28, and 35. All pigs given 0.1 ug/kg PMT without serum died or were euthanized as were 4 pigs given 0.05 ug/kg. These pigs had increased serum levels of IL-1 and IL-6 bioactivity. Those pigs surviving 0.05 ug toxin had decreased weight gain, rough hair coats, marked atrophy of the ventral concha, and small stature. The surviving pigs also had reduced physeal area and decreased proliferation indices in physeal chondrocytes based on bromodeoxyuridine immunoreactivity (BrDU-IR). Control pigs and serum-treated pigs gained weight, had no clinical effects, had similar physeal areas, and had higher cell proliferation indices. This study demonstrates that PMT inhibits endochondral bone formation by reducing physeal area and chondrocyte proliferation in vivo. Hyperimmune serum neutralizes the effects of toxin on weight gain, clinical appearance, physeal area, and chondrocyte proliferation.