Ultrastructural studies of a visna-like syncytia-producing virus from cattle with lymphocytosis.

A virus structurally similar to viruses associated with maedi, progressive pneumonia, and visna of sheep has been isolated from buffy coat cells of cattle with chronic lymphocytosis. Electron microscope studies revealed three variants of the virion: (i) an intracytoplasmic form 98 to 116 nm in diameter when occurring in a nonlaminated form, (ii) a budding form 120 to 130 nm in diameter, and (iii) an extracellular form 80 to 130 nm in diameter and containing a 30 to 43 nm eccentrically located electron-dense core.