Effective transmission of a virus from one host to another depends to on the concentration of shed virus, the mechanism by which the virus is introduced into the next host, and sometimes, environmental factors. Cell injury Viruses cause injury to cells either directly or indirectly. Recent studies using depletion of particular immune cells, knockout mice, and adoptive transfer have demonstrated the role of these cells in causing cell and tissue injury. Other mechanisms by which virus induce immunopathology are by superantigen production. NO, which is produced in abundance during the early innate immune response to virus has been shown to inhibit virus replication.
Viruses can also affect the infected host without directly injuring the cell.
For example LCMV infection of newborn mice produced persistent infection in which the virus replicates in the pituitary glands that produces growth hormones. As a result, the mice fail to grow and die within a month. G. Transformation and Oncogenesis Oncogenesis is the mechanism for development of cancer. In many cases, such transformed cells were shown to induce tumors upon transplantation into animals. The most important step in cell transformation is immortalization , an ability to divide indefinitely.