The ultrastructure of the developing replication site in foot-and-mouth disease virus-infected BHK-38 cells

Foot-and-mouth disease virus (FMDV) is the type species of the Aphthovirus genus of the Picornaviridae. Infection by picornaviruses results in a major rearrangement of the host cell membranes to create vesicular structures where virus genome replication takes place. In this report, using fluorescence and electron microscopy, membrane rearrangements in the cytoplasm of FMDV-infected BHK-38 cells are documented. At 1-5-2.0 h post-infection, free ribosomes, fragmented rough endoplasmic reticulum, Golgi and smooth membrane-bound vesicles accumulated on one side of the nucleus. Newly synthesized viral RNA was localized to this region of the cell. The changes seen in FMDV-infected cells distinguish this virus from other members of the Picornaviridae, such as poliovirus. Firstly, the collapse of cellular organelles to one side of the cell has not previously been observed for other picornaviruses. Secondly, the membrane vesicles, induced by FMDV, appear distinct from those induced by other picornaviruses such as poliovirus and echovirus 11 since they are relatively few in number and do not aggregate into densely packed clusters. Additionally, the proportion of vesicles with double membranes is considerably lower in FMDV-infected cells. These differences did not result from the use of BHK-38 cells in this study, as infection of these cells by another picornavirus, bovine enterovirus (a close relative of poliovirus), resulted in morphological changes similar to those reported for poliovirus-infected cells. With conventional fixation, FMDV particles were not seen; however, following high-pressure freezing and freeze-substitution, many clusters of virus-like particles were seen.