Abstract: To investigate the major steps in the replicative cycle and ultrastructural changes during pseudorabies virus (PRV) infection, the swine testis (ST) cell line was used as the target cell to be infected with PRV Ra strain. The results demonstrated that PRV could cause obviously cytopathic effect, with a close relation with the PRV infected time. According to the observation by electron microscopy, PRV virions attached to the cell surface were found in the initial stage of infection, virus entered into cells and cell nuclear area by membrane fusion and endocytose, then began to replicate in the nucleuses, virus envelop was obtained from the membrane structure in the cytoplasm, especially in the Golgi body;the mature PRV particles were released into the extracellular to infect other cells during the early stages of infection;and the virus particles were released by cytolysis in the later stages. Ultrastructural changes of infected cells showed mitochondria swelling,decreased,cristae vague, intranuclear inclusions, cell fusion, serious cavitation and cytolysis.

Key words: pseudorabies virus Ra strain; ST cell; cytopathic effect; ultrastructure