Spontaneous listeric encephalitis in sheep. Electron microscopic studies

The brainstems of four sheep with spontaneous listeric encephalitis had scattered small foci of inflammatory cells (neutrophils or macrophages, or both) with scattered fragments of degenerating nerve fibers and glial cells. In extensive areas of malacia in the pons and medulla oblongata, there was loss of parenchyma with massive accumulation of macrophages, a few neutrophils, lymphocytes and plasma cells. In both types of lesions, phagocytes contained debris of myelin and axons, lipid vacuoles and occasionally bacteria. Neutrophils contained bacteria in phagocytic and digestive vacuoles. No bacteria were detected in macrophages but were detected in neurons and in one axon in tissue previously used for paraffin sections.