Abstract: Objective To investigate the mitochondrial injury in enterovirus 71 (EV71)-infected Vero cells and explore the
possible mechanism. Methods A clinical isolate of EV71 was inoculated to Vero cells and the EV71 antigen was detected by
immunofluorescence assay. The morphological changes of Vero cells were observed using optical microscopy and transmission
electron microscopy. The diameter and area density of the viral particles and the ratio and area density of vacuolated
mitochondria in the cells were measured on the ultrastructural images. Results EV71-infected Vero cells underwent obvious
changes and to a spherical morphology followed by cell death EV71 particles were detected in the cytoplasm by
immunofluorescence. Ultrastructurally, the infected cells contained a large number of viral particles in the cytoplasm, with a
clustered distribution and lattice-like arrangement. The diameter of the particles were 16.3 nm and the mean area density was
38.3% . Most of the mitochondria presented with swelling, vacuoles and degeneration. The ratio of the vacuolated
mitochondria was 90.9% with a mean area density of 89.2%. Viral particles were also found in some mitochondria. Conclusion
EV71 proliferates in the cytoplasm and invades the mitochondria of infected Vero cells leading to mitochondrial injury and cell
death, suggesting that mitochondria are the targets for EV71 infection.