Cytomegalovirus (CMV) is a member of the Herpesviridae family, specifically classified as a betaherpesvirus.:
1. **Structure**:
- **Genome**: CMV has a linear large double-stranded DNA genome of approximately 235 kilobases, encoding more than 200 proteins.
- **Capsid**: The genome is enclosed in an icosahedral capsid.
- **Tegument**: Surrounding the capsid is a proteinaceous layer called the tegument.
- **Envelope**: The outermost layer is a lipid envelope derived from the host cell membrane, embedded with viral glycoproteins necessary for entry into host cells.
2. **Replication Cycle**:
- **Attachment and Entry**: CMV enters host cells by binding to cell surface receptors and fusing with the cell membrane.
- **Immediate-Early Phase**: After entry, immediate-early genes are expressed, which regulate viral replication and modify the host cell environment.
- **Early Phase**: Early genes are expressed, leading to DNA replication.
- **Late Phase**: Late genes are expressed, producing structural proteins for new virions.
- **Assembly and Egress**: New virions are assembled in the nucleus, transported to the cytoplasm, and released by budding from the cell membrane.
3. **Host Interaction and Pathogenesis**:
- **Cell Types**: CMV can infect a wide range of cell types, including fibroblasts, epithelial cells, endothelial cells, smooth muscle cells, and leukocytes.
- **Latency and Reactivation**: CMV establishes lifelong latency in the host, particularly in monocytes and their progenitors. Reactivation can occur under conditions of immunosuppression.
- **Immune Evasion**: CMV has evolved numerous mechanisms to evade the host immune response, including downregulation of major histocompatibility complex (MHC) molecules, inhibition of natural killer (NK) cell activity, and modulation of cytokine production.
4. **Clinical Implications**:
- **Congenital CMV Infection**: CMV is a leading cause of congenital infections, which can result in hearing loss, developmental delays, and other long-term health issues.
- **Immunocompromised Individuals**: In individuals with weakened immune systems, such as transplant recipients and HIV/AIDS patients, CMV can cause severe, potentially life-threatening illnesses, including retinitis, pneumonitis, gastroenteritis, and hepatitis.
Understanding the microbiology of CMV is crucial for developing targeted antiviral therapies and preventive measures, such as vaccines, to control and mitigate its impact on public health.