Fig. (1).

Electron microscopic visualization of morphology of cytomegalovirus particles. Human foreskin fibroblasts were inoculated with the Toledo strain of cytomegalovirus and, following 7 days of incubation, cells were fixed with paraformaldehyde, stained with phosphotungstic acid, and visualized by EM (University of Minnesota). A) Image demonstrating cell-associated virus particles [virions and dense bodies (DB)]. B) Comparison of mature virion and non-infectious enveloped particle (NIEP, arrow), which contains capsid proteins but no DNA and is hence replication-defective. C) Comparison of virions and DB (arrow). In contrast to virions, DB are larger, contain no viral DNA and no capside proteins, and are non-infectious.