IMMUNOHISTOCHEMICAL AND PATHOLOGICAL-STUDY OF MYCOPLASMA BOVIS-ASSOCIATED LUNG ABSCESSES IN CALVES

Out of 45 cases of fatal chronic pneumonia in calves examined for Myco plasma bovis infection from February to July 1994, 11 cases with pulmo nary abscesses that were culture positive for M. bovis were encountere d. The cases were studied in detail using a recently developed monoclo nal antibody-based immunoperoxidase technique. Mycoplasma bovis organi sms were detected in specific locations at all stages of abscessation observed. In bronchioles or terminal ah-ways within which abscesses de veloped, M. bovis was located at the epithelial surface and in close a ssociation with infiltrating neutrophils and macrophages. Abscessed ai rways that had lost the epithelium were encapsulated and were seen as coagulative necrotic foci that stained intensely for M. bovis, especia lly at the periphery. Some foci stained weakly and such might have bee n resolving lesions. Mycoplasma bovis was also demonstrated at sites o f mild mononuclear cell infiltration in the livers and kidneys of 2 ca lves. The mycoplasma was detected within bile ducts in the liver and i n the tubular epithelium of the kidney. Abscesses not staining for M. bovis, presumably caused by other pathogens, were seen concurrently wi th M. bovis-associated abscesses in some lungs. Thirteen other M. bovi s-positive cases showed no abscesses, possibly indicating heterogeneit y among M. bovis strains. Three other cases with abscesses were negati ve for M. bovis by culture and immunoperoxidase staining. The monoclon al antibody-based immunohistochemical technique is efficient for speci fic detection of M. bovis in cases of enzootic pneumonia of calves wit h or without abscessation. Mycoplasma bovis is implicated in the patho genesis of lung abscesses in some calves.