Ultrastructural Changes in Cells Induced by Temperature-sensitive Mutants of Fowl Plague Virus at Permissive and Non-permissive Temperature

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Abstract
Ultrastructural changes developing in chick embryo fibroblast cultures infected with a wild-type strain of fowl plague virus (FPV) or one of six FPV temperature-sensitive (ts) mutants belonging to different complementation groups were studied. Cells infected with wild-type FPV and incubated at optimal (36 °C) or nonpermissive temperature (42 °C) displayed changes similar to those described for orthomyxoviruses. The same patterns of changes were observed at 36 °C in cells infected with ts mutants belonging to five of the complementation groups. Mutant ts 303, possessing mutation-altered haemagglutinin, induced at 36 °C the formation of virions carrying a considerably reduced number of spikes on their surfaces. At 42 °C, cells infected with ts mutant 131, with a defective primary transcription stage, showed no morphological changes and no formation of electron-dense inclusions. Cells infected with ts mutants with defective secondary transcription or replication displayed nuclear inclusions but no formation of filamentous cytoplasmic structures or virions. Mutant ts 5 with defective late morphogenesis induced formation of considerably enhanced numbers of nuclear inclusions.