Cytomegalovirus (CMV), also known as human herpesvirus 5, is a large enveloped double‑stranded DNA virus belonging to the Betaherpesvirinae subfamily. It infects a wide range of cell types and is notable for causing congenital infection and severe disease in immunocompromised hosts.
Biology and Pathogenesis
CMV has a four‑layered structure similar to other herpesviruses, with a double‑stranded DNA core encased in an icosahedral capsid, surrounded by a tegument and lipid envelope bearing glycoproteins. The virus replicates slowly in epithelial cells, leukocytes and endothelial cells. During primary infection, high levels of virus are produced in salivary glands and kidneys, and the virus is shed in saliva, urine, breast milk and genital secretions. Transmission occurs through intimate contact with infected bodily fluids, transplacental spread, perinatal exposure, sexual contact, transfusion and organ transplantation. After primary infection, CMV persists in a latent state within monocytes and other cells. Reactivation may occur during immunosuppression or inflammation. In utero infection arises when the virus crosses the placenta; it can damage the developing fetus, leading to hepatosplenomegaly, jaundice, microcephaly, hearing loss and developmental delay. In older children and adults, primary CMV infection often causes a mononucleosis‑like syndrome with prolonged fever, fatigue and atypical lymphocytosis but negative heterophile antibody tests. The immune response to CMV involves both humoral and cellular components, which usually contain the virus without eliminating latent genomes. In immunocompromised individuals, especially transplant recipients and people with advanced HIV infection, reactivation or primary infection can result in severe disseminated disease affecting the lungs, gastrointestinal tract, retina and central nervous system.
Major Clinical Syndromes
Congenital CMV infection is the leading infectious cause of sensorineural hearing loss and can also cause growth restriction, chorioretinitis and neurologic deficits. Infants born with symptomatic congenital CMV may show jaundice, petechiae and intracranial calcifications. A mononucleosis‑like illness due to CMV features fever, malaise and lymphocytosis but lacks the heterophile antibodies seen in Epstein–Barr virus infection. Recovery is typically spontaneous in immunocompetent hosts. In organ transplant recipients, CMV is a major cause of interstitial pneumonitis, colitis and hepatitis; prophylactic or preemptive antiviral therapy is often used to prevent these complications. Patients with advanced HIV infection may develop CMV retinitis characterized by retinal necrosis leading to vision loss. The virus can also cause esophagitis and colitis in the setting of AIDS. CMV is an omnipresent DNA virus that spreads via bodily fluids, establishes lifelong latency and reactivates when immunity wanes. It causes congenital disease, mononucleosis‑like illness and serious opportunistic infections. Preventive measures include screening blood and organ donors and using antiviral prophylaxis in high‑risk patients. Related Terms: Epstein–Barr Virus, Varicella‑Zoster Virus, Human Herpesvirus 6, Human Herpesvirus 7, Kaposi’s Sarcoma‑associated Herpesvirus