Virus replication is often detected by the morphological changes, or cytopathic effects (CPE), that are seen in infected cell cultures. Figures 1 (x100) and 2 (x400) illustrate the CPE typical of measles virus infection of the human HeLa cell line. The large syncytia, or multinucleated giant cells, result from fusion of cell membranes bearing viral glycoproteins. Also visible in this culture (Fig. 2) are inclusion bodies, which are seen as eosinophilic areas of altered staining in the cytoplasm. In order to view these cellular changes under light microscopy, the cell cultures have been stained with hematoxylin, a basic dye, and eosin, an acidic dye. The cell culture is shown 7 days after virus inoculation.

For comparison, Fig. 3 (x100) and Fig. 4 (x400) show the uninfected Vero cell line at 48 h after seeding of the culture. In Fig. 4, several nucleoli are visible inside each nucleus. Cells have been stained with hematoxylin, a basic dye, and eosin, an acidic dye. Note the eosinophilic cytoplasm (pink) and basophilic nuclei (purple).

These images can be used to help students visualize viral CPE.