Human cytomegalovirus, commonly abbreviated as HCMV, is a member of the Herpesviridae family and belongs to the subfamily Betaherpesvirinae. It is an enveloped virus with a large, linear, double-stranded DNA genome and is one of the most complex viruses known to infect humans.

HCMV enters host cells either by membrane fusion or endocytosis, depending on the cell type. Following entry, the viral genome is transported to the nucleus, where viral DNA replication and gene expression take place. New viral particles are initially assembled in the nucleus before undergoing further maturation in the cytoplasmic viral assembly compartment. Mature virions are then released from the infected cell, primarily through exocytosis.

The HCMV genome is among the largest of all human viral genomes and encodes more than 170 proteins. These include structural proteins required for virion formation, as well as numerous regulatory proteins that alter host-cell pathways, support viral replication, and promote immune evasion. A key feature of HCMV infection is its ability to establish lifelong latency, mainly within cells of the myeloid lineage. During latency, the virus persists in a dormant state but can periodically reactivate, particularly in individuals with weakened or suppressed immune systems.

Transmission occurs through direct contact with infected bodily fluids, including saliva, urine, blood, breast milk, semen, and cervical secretions. HCMV may also be transmitted through organ transplantation, blood transfusion, and from mother to foetus during pregnancy. Congenital transmission is especially significant, as HCMV is the most common cause of congenital viral infection worldwide.

In immunocompetent individuals, HCMV infection is often asymptomatic or may cause a mild, mononucleosis-like illness characterised by fever, fatigue, and lymphadenopathy. In contrast, HCMV can cause severe and potentially life-threatening disease in immunocompromised individuals, including transplant recipients, people living with HIV, and patients receiving immunosuppressive therapies. In congenital infection, HCMV may lead to sensorineural hearing loss, neurodevelopmental impairment, visual defects, seizures, and other long-term complications. It is therefore recognised as a leading infectious cause of birth defects and childhood disability.

Seroprevalence studies estimate that HCMV infects approximately 50-90% of the global adult population, although prevalence varies according to geographic region, age, socioeconomic status, and population group. Congenital HCMV infection occurs in approximately 1 in 200 live births, representing a substantial healthcare burden due to its potential for lifelong disability and associated medical costs.

Several antiviral drugs, including ganciclovir, valganciclovir, foscarnet, and letermovir, are used for the treatment or prevention of HCMV infection in high-risk patients. However, their clinical use is limited by toxicity, antiviral resistance, drug interactions, and limited activity against latent infection. Despite decades of research, there is currently no licensed vaccine for HCMV. This highlights the continuing need for improved preventive strategies, safer antiviral therapies, and effective vaccine development.

Overall, HCMV is a highly prevalent and medically important human pathogen. While infection is usually mild or silent in healthy individuals, it poses a major risk to immunocompromised patients and developing fetuses, making it an important focus of clinical, virological, and public health research.