Final answer:
The owl's eye appearance in a giant cell signifies the presence of cytomegalovirus (CMV), which is also known as HHV-5.
Step-by-step explanation:
The "owl's eye" appearance in a giant cell, as shown in Figure 21.9, indicates the presence of cytomegalovirus (CMV). CMV causes cells to become enlarged and develop a characteristic nucleus that resembles an owl's eye. CMV is also known as human herpesvirus 5 (HHV-5). It can lead to serious congenital infections as well as diseases in immunocompromised adults.
Comparing the diseases caused by HHV-4 and HHV-5, HHV-4, known as Epstein-Barr virus, is associated with infectious mononucleosis and Burkitt lymphoma, whereas HHV-5 (CMV) may cause serious congenital and immunocompromised conditions. Neither dengue virus nor Ebola virus is associated with this characteristic owl's eye appearance in infected cells.