Some Features of Pulmonary Mycoplasmosis in Groups of Naturally Infected Calves

Abstract

Several species of bacteria and mycoplasma were isolated from groups of conventional calves housed together for specific periods of time, during which respiratory disease was observed in some animals. The cumulative results suggested that Mycoplasma dispar was closely associated with Lesions of cuffing pneumonia amongst naturally infected calves. Mycoplasma bovirhinis, Acholeplasma laidlawii and Ureaplasma sp. were also recovered, but isolations were as frequent from non-pneumonic as pneumonic tissue.

M. dispar is not readily isolated by direct lung culture and a 50% recovery rate from lesions of cuffing pneumonia may be expected. Mycoplasmas can be detected indirectly by immunofluorescence and electron microscopy.

In cuffing pneumonia, as in pulmonary mycoplasmosis in other hosts, there is a massive infiltration of lymphocytes around the airways forming cuffs of cells which do not appear to be antibody producing. Another characteristic of cuffing pneumonia is a marked increase in mucus production and an alteration in its composition.

In many calves mycoplasmas were detected by electron microscope in the bronchial epithelium but were seldom identified in alveolar tissue. The organisms were always extracellular and formed a close association with the cilia and microvilli of the epithelium. Mycoplasmas with extracellular capsules were recognised in pulmonary tissue treated with ruthenium red — a feature associated with M. dispar.

Changes in the ultrastructure of the bronchial epithelial cells were apparent in some cases; many cells lost their cilia and the cytoplasm of the epithelial cells protruded into the lumen. The mitochondria were often distended and disrupted and vacuoles were recognised in the cytoplasm.