Cytomegalovirus Disease

Cytomegalovirus spreads through infected body fluids via blood transfusion, organ transplant, sexual contact, and from mother to fetus during pregnancy. The virus can also transmit through other bodily fluids in close contact situations. Once transmitted, it establishes lifelong latency primarily in monocytes and hematopoietic progenitor cells, where it persists indefinitely.

When immunity weakens after organ transplant or immunosuppressive therapy, latent CMV reactivates and takes over host cells to produce new virions. The virus spreads systemically, causing severe complications like pneumonia, retinitis, colitis, or encephalitis. In contrast, immunocompetent individuals typically develop only a mononucleosis-like illness.

CMV interferes with MHC class I antigen presentation, preventing CD8⁺ T cells from recognizing infected cells. Viral proteins also attach to host chemokines, hindering immune cell recruitment to infection sites. Additionally, CMV microRNAs suppress translation of MHC-related proteins, further blocking immune recognition and allowing persistent infection.

Congenital CMV occurs when the virus crosses the placenta during maternal viremia, particularly in primary infections during the first trimester. Infected neonates may develop jaundice, petechiae, hepatosplenomegaly, microcephaly, hearing loss, and periventricular calcifications. CMV is the most common cause of congenital viral infection in the United States.

Virus-infected cells, especially in epithelial tissues, become enlarged and develop characteristic intranuclear inclusion bodies visible under a microscope. These distinctive cytopathic changes help identify CMV infection during diagnostic examination. The enlarged cells with inclusion bodies are a hallmark of active viral replication.

Diagnosis relies on serologic assays measuring IgM and IgG avidity, and molecular tests such as PCR for viral load assessment. Antiviral agents like ganciclovir, valganciclovir, foscarnet, and cidofovir treat CMV disease, particularly in high-risk populations including transplant recipients. No vaccine is currently available, though candidates are under investigation.

Solid organ and hematopoietic stem cell transplant recipients receive immunosuppressive therapy to prevent rejection, which weakens cell-mediated immunity. This allows latent CMV to reactivate spontaneously, causing systemic infection and severe complications. CMV is a major pathogen in transplant populations, making prophylaxis and monitoring essential. Understanding viral meningitis and other opportunistic infections helps contextualize CMV's role in immunocompromised patients.