Viral replication refers to the process by which a virus reproduces itself within a living organism. This generally involves turning infected cells into virus factories, which manufacture copies of the virus's genetic code and expel them to spread into the host body. This turns the infected body against itself, using its own cells as tools of mass production and infection.
Once a virus infects the host body, it targets different types of living cells, depending on its nature. The virus begins by attaching itself to a vulnerable cell, then penetrating its surface, or in some other way infusing itself into the primary substance of the host cell. Different viral types have different ways of gaining entry into the cellular body or fusing themselves with the cellular wall, but generally the process involves compromising the cell's integrity. At this point the viral replication process ensues, in which the virus takes over the cell's own reproductive functions and reprograms it to create copies of the virus's DNA or RNA. The viral replication process continues until the cell bursts in a stage called shedding, releasing multiple duplicates of the original virus into the host body. Each copy targets more susceptible cells, attaches, and begins the replication process anew.
The stages of replication vary for different types of viruses, such as the diverse combinations of double-stranded and single-stranded, positive or negative, DNA or RNA viruses. Many types require specific conditions within a host cell before viral replication can begin. Some are capable of replicating despite the host cell's state, making them more virulent and more dangerous.
Other kinds of viruses can only replicate in certain types of cells, while some can enter cells, replicate for a time, and then remain dormant within the cell for unspecified periods. This dormant period is called latency, and it can last until a triggering factor reactivates the virus and causes it to once more begin reproducing in the host cell.
The study of viral replication has been key to understanding virulent diseases, such as herpes and HIV-AIDS. Viral latency in HIV causes it to insert itself into key areas of the host cell's nucleus, making it a nearly inseparable part of the cell's normal replication process. Understanding the viral reproduction cycle and methodology allows researchers to propose theories on extracting the virus, preventing the conversion of host DNA into viral DNA, or preventing it from penetrating the host cell to begin the infection process.