Cytomegalovirus or human herpesvirus 5 (HSV-5) is the causative agent of mononucleosis syndrome in symptomatic infection in immunocompetent hosts. It causes pneumonia and more serious diseases in immunocompromised patients than in other individuals. The name is originated from the word cytomegalo (large cell virus) and is derived from the swollen cells containing large multinuclear inclusions that characterize these infections.
Cytomegalovirus is a member of the Betaherpesvirinae in the subfamily Herpesviridae. The virus shares similar common fea-tures in the structure, genome, and potency to cause latent and persistent infections like those of other herpesviruses.
Cytomegalovirus shows following features:
· CMV is the largest herpesvirus measuring 150–200 nm in size.
· It has the largest genome of all the herpesviruses, ranging from 230 to 240 kbp. It is a double-stranded linear DNA virus with 162 hexagonal protein capsomeres surrounded by a lipid membrane.
· CMV is the only beta herpesvirus that has the only class E genome, similar to that present in HSV.
Replicative cycle of CMV is similar to that of other herpesvirus, except that some of the immediate early proteins of the CMV are translated from mRNAs incorporated into the infected cells by the parental virion, but are not translated from the mRNAs synthesized in the newly infected cells.
Human CMV has a single serotype. It does not show any antigenic cross-reaction with CMV of other mammalian species. It shows only minor antigenic cross-reaction with simian CMV.
Human CMV replicates only in human cells. The virus grows only in diploid human fibroblast cell culture but not in epi-thelial cell culture. CMV grows very slowly in these cell lines, taking as long as 4–6 weeks to produce characteristic CPEs. The CPE includes foci of swollen refractile cells with cytoplasmic granules, which can be demonstrated by staining. In a stained smear, these cells show multinucleated giant cells containing acidophilic inclusions in the nuclei and cytoplasm.