According to MedlinePlus, viruses replicate by invading normal cells and using those cells to produce viruses like themselves. Familiar infections caused by viruses include the common cold, warts and HIV/AIDS.
Viruses either stay inside of the body or organs that they infect, or they spread to other people, according to the University of Rochester Medical Center. All viruses need a host cell in order to begin reproducing. Viruses can eventually interfere with the host cell's normal processes and explode out of it, which usually kills the host cell and leads to illness.
The University of Rochester Medical Center also notes that while some viruses actively reproduce, others can lie dormant in the body. In such cases, the virus harmlessly rests inside of the host cell and does not reproduce. This dormant virus can eventually become active and cause damage to tissues and organs, but this is not always the case. It is also possible for nonreactive viruses to become active and then return to their dormant state.
According to Drugs.com, antiviral drugs can be used to target specific strains of viruses, but these drugs do not kill the virus. Antiviral drugs inhibit the reproduction of viruses and keep them from attaching to the host cell, thus interfering with the infection process.