A Morphological Study of Outfolded and Released Parainfluenza Type 3 Virus

Elongated protrusions (diam. 150 to 250 nm) extending from the cell membranes, have been observed by scanning electron microscopy and in thin sections of calf kidney cells 10 h after infection with high multiplicities of parainfluenza virus 3 (PIV-3).

Unfixed, flattened PIV-3 particles, were pleomorphic with diam. ranging from 100 to 500 nm. Following early fixation of fresh virus harvests, the particles appeared spherical in the scanning and transmission electron microscopes, and had a mean diam. of 135 nm. These virus particles had not been flattened on the support film as demonstrated by goniometer analysis.

Spontaneous segmentation of unfixed PIV-3 envelopes was observed. Phospholipase C digestion of the virus resulted in a similar segmentation, producing round envelope aggregates with extending peplomers.