Murine cytomegalovirus (MCMV) belongs to the genus cytomegalovirus (CMV) of the β-Herpesvirinae subfamily of the Herpesviridae family. CMVs are marked by strict species specificity, tropism for hematopoietic tissue and secretory glands, and a slow replication cycle. After the resolution of acute infection, CMVs establish persistent life-long infections characterized by alternate stages of virus productivity and latency. Although producing up to 200 potentially antigenic proteins during its sequential immediate early (IE), early (E) and late (L) phases of gene expression, transmission to a new host is achieved in the face of repeatedly primed antiviral immune responses.
The routes used by MCMV to enter the host have not yet been clearly determined. Infectious virus can easily be detected in saliva of chronically infected mice, and productive infection is confined to glandular epithelial cells of salivary glands for a prolonged period of time, even in a fully immunocompetent host. Therefore, it is likely that the saliva is the major source of virus for horizontal spread, and the major route of entry for MCMV is the epithelium of the gastrointestinal and the upper respiratory tract. Per oral infection of newborn mice with MCMV leads to virus spread similar to that following intraperitoneal virus administration, which confirms that MCMV can enter through the epithelium of the gastrointestinal and/or respiratory tract. In addition, sexual transmission of MCMV and viral entry through the epithelium of the genitourinary tract could be an important means of its horizontal spread. After entry into the host, the virus spreads haematologically to various organs and infects many different cell types, including epithelial and endothelial cells, myocytes, brown fat adipocytes, fibrocytes, macrophages and bone marrow (BM) stromal cells (Krmpotic et al., 2003). |
