Virology and Epidemiology
Cytomegalovirus (derived from Greek cytos — cell and megas — large) belongs to the family Herpesviridae, genus Cytomegalovirus. It was first isolated by C. Smith in 1956. Among all herpesviruses, it possesses the largest DNA genome. In laboratory conditions, the virus replicates exclusively in human cells (fibroblasts, epithelial cells, macrophages), although pathogenicity in non-human primates is also documented.
When cultured in fibroblasts, the virus exerts a marked cytopathic effect, inducing specific intranuclear inclusions and the formation of giant cytomegalomegalic cells. In the environment, the pathogen is extremely labile: it is heat-sensitive and highly susceptible to standard disinfectants and lipid solvents.
Sources and Transmission The infection is widespread. Humans—both symptomatic patients and asymptomatic carriers—are the sole reservoir and source of infection. The virus is actively shed in urine, saliva, semen, breast milk, and circulates in the blood.
Ports of entry include mucous membranes, broken skin, respiratory tracts, and the placenta. Main transmission mechanisms include:
- Direct contact and respiratory droplets
- Fecal-oral route
- Sexual contact
- Parenteral route (blood transfusions, organ transplantation)
- Transplacental route (leading to congenital infection)
Pathogenesis and Clinical Presentation
In most cases, primary infection resolves into a latent state that persists for life. The virus shows a marked tropism for epithelial cells of the salivary glands and renal tubules, where replication occurs. The primary cellular reservoirs for latency are mononuclear leukocytes and bone marrow stromal cells. An exact incubation period is difficult to establish due to frequent subclinical courses.
Acute manifest infection or viral reactivation occurs in the setting of cellular immunosuppression. High-risk groups include immunocompromised individuals, solid organ transplant recipients, and pregnant women. In approximately 95% of AIDS patients, CMV acts as a severe opportunistic infection.
Spectrum of Clinical Manifestations:
- Acquired Infection: May lead to central nervous system involvement with cognitive impairment, visual and hearing loss, and severe visceral pathologies such as interstitial pneumonia. A notable severe complication is triggering Guillain-Barré syndrome—a demyelinating polyradiculoneuropathy presenting with paresis and paralysis. The virus is also hypothesized to possess oncogenic potential (e.g., association with prostate adenocarcinoma).
- Congenital Infection: Represents the greatest hazard and is diagnosed in roughly 1% of newborns resulting from transplacental transmission. Clinical features include severe jaundice, hepatosplenomegaly, ocular damage, cachexia, and multiple congenital anomalies (including microcephaly). The prognosis is frequently poor and can be fatal.
Diagnostics, Treatment, and Prevention
In response to viral invasion, the host mounts both humoral and cellular immune responses. However, the production of specific neutralizing antibodies does not clear persistent virus from cells.
Microbiological Diagnostics Diagnostic specimens include blood, urine, saliva, breast milk, cerebrospinal fluid (CSF), and cervical secretions.
- Cytological assay: Aims to detect giant cells measuring 25–40 µm. Hematoxylin and eosin staining clearly visualizes intranuclear inclusions, forming the classic "owl's eye" appearance.
- Virological assay: Isolation of the pathogen in cell culture.
- Identification and serology: PCR, direct immunofluorescence (DFA), and ELISA utilizing monoclonal antibodies confirm the diagnosis. Serologic testing involves measuring specific IgM and IgG antibodies (via ELISA, complement fixation, and neutralization assays).
Management and Prevention First-line antiviral therapy relies on nucleoside analogues (ganciclovir, valganciclovir, foscarnet, cidofovir). Immunomodulatory approaches include interferon inducers, interferons, and normal human immunoglobulin.
There is no widely available licensed vaccine against CMV. Non-specific prevention relies on isolating high-risk individuals from potential sources. Notably, infants with congenital CMV shed the virus actively for up to 5 years. When planning future pregnancies after delivering an infant with congenital CMV infection, it is strongly recommended to delay subsequent pregnancy for at least 2 years to account for the duration of maternal viral persistence.