The Ultrastructural Changes Produced by Infectious Laryngotracheitis Virus in Tracheal Epithelium of the Fowl

Abstract

SUMMARY The ultrastructural changes produced by infectious laryngotracheitis virus in the tracheal epithelium of minimal diseased fowls are described. The giant cell structures seen using the light microscope were identified as syncytia. Virus particles were first seen in the nuclei and in cytoplasmic vacuoles of the syncytia on the third day after exposure. The majority of the particles within the nucleus consisted of a core and capsid only. By the fourth day after infection most of the virus particles within the nucleus had acquired an outer envelope and were most often seen close to or between the layers of the nuclear membranes. Structures morphologically consistent with inclusion bodies were present on the third and fourth days after exposure and consisted of fine granular electron dense material through which a few unenveloped particles were scattered. Regeneration commenced with the spread of a single layer of cells over the surface of the lamina propria. Mitotic figures were numerous in the regenerating epithelium on the sixth and seventh days after exposure when several layers of these cells had formed. Numerous microvillus-like processes were seen extending from the regenerating epithelial cells on the ninth day after exposure and cilia were first seen on the tenth day. By the twelfth day the epithelium appeared normal.