Submitted to: Pig Veterinary Society International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 7, 2000
Publication Date: N/A
Bordetella bronchiseptica is one of the etiologic agents causing atrophic rhinitis and pneumonia in swine. B. bronchiseptica produces several purported virulence factors, such as adhesins and toxins, including the dermonecrotic toxin (DNT). The purpose of this experiment was to determine the role of this toxin in pathogenesis by comparing the pathogenicity of an nisogenic DNT**- mutant to its virulent DNT**+ parent strain. The DNT**- mutant of B. bronchiseptica was much less pathogenic than the DNT**+ parent strain, when comparing the nasal turbinate atrophy and pneumonia induced by the two strains. The results of the nasal washes indicated colonization of the nasal cavity was statistically lower for the mutant as compared to the parent strain. At necropsy the mean colonization of the nasal turbinate and trachea was higher for the DNT**+ parent, but due to variation this difference was not statistically significant. It is possible that DNT aids sin colonization of the nasal and tracheal mucosa, and it could be argued that the increased colonization levels of the nasal cavity could have been partially responsible for the increased degree of nasal turbinate atrophy seen in the pigs inoculated with the parent strain. However, the mutant was able to colonize efficiently and the differences seen in the degree of atrophy appear too great for DNT not to be playing a major role in the atrophy process. The mean level of colonization of the lung was actually greater for the DNT**- mutant than for the parent strain, although this difference was not statistically significant. The fact that the DNT**- mutant colonized the lung with essentially no evidence of pneumonia, while all pigs inoculated with the parent DNT**+ strain had pneumonia, argues strongly for the involvement of DNT in inducing pneumonia in pigs.