HISTOMORPHOLOGIC FEATURES OF THE NASAL CAVITY OF PIGS EXPOSED TO PASTEURELLA-MULTOCIDA TYPE-D DERMONECROTIC TOXIN

Microscopic examination of the nasal mucosa of clinically normal speci fic-pathogen-free pigs and of toxicogenic type-D Pasteurella multocida toxin challenge-exposed specific-pathogen-free pigs indicated that th e surface epithelium in pigs of both groups was microscopically normal ; erosions or appreciable inflammatory changes were not evident. In pi gs of both groups and in all 3 regions of the nasal cavity, the endoth elial lining of all blood vessels appeared normal without detectable c hanges to the walls at postinoculation day 10. Vascular injury in the cartilage or the bone was not discernible in control or challenge-expo sed pigs. There were marked differences in the osseous structures of t he conchae when the 2 groups were compared. In control pigs, active bo ne formation and remodeling were observed, and the septal cartilage wa s normal. In toxin challenge-exposed pigs, there likewise was normal b one formation and remodeling in the vestibular region, and the septal cartilage was normal. In marked contrast, conspicuous changes were obs erved in the osseous core of the conchae of the respiratory and, somet imes, the olfactory regions. These changes consisted of bone necrosis and resorption by large numbers of osteoclasts with variable replaceme nt by dense mesenchymal stroma, which resulted in conchal atrophy. in the absence of any discernible damage or injury (angiopathy) to the na -sal vessels, it appears that the action of the dermo-necrotoxin of P multocida serotype D is on the most active osteoblasts and the associa ted organic matrix of the bone, with subsequent disruption of normal b one formation and remodeling of the nasal conchae.