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Abstract
Fowls were infected with avian-IBV and, subsequently, their tracheas were sectioned and examined in the electron microscope. The lining epithelial cells showed extensive loss of cilia, degeneration of microvilli, swelling of mitochondria, increased amount of endoplasmic reticulum and of other intracellular membranes, and the presence of electron-dense areas in the cytoplasm. Virus particles were first observed about 12 hr after infection within the electrondense areas and within spaces between the membranes of the endoplasmic reticulum. By 48–72 hr they were considerably more numerous and were present mainly within cisternae and vesicles formed from the membranes of the endoplasmic reticulum. There was little evidence of budding. The mature virus particle had a mean diameter of 81±1 nm and possessed both inner and outer electron-dense coats or shells separated by an electron-transparent layer. Virus particles grown in the embryonated hen egg and harvested from the allantoic fluid had a similar size and structure.
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