Virus Reproduction

The reproduction of viruses involve two phases, the lysogenic cycle and the lytic cycle. Viruses usually skip the lysogenic cycle and go straight to the lytic cycle thus causing disease shortly after infection. Some viruses however go through the lysogenic cycle first, remaining dormant in the host until a certain trigger is supplied which causes the virus to go into the lytic cycle.

The first phase of virus reproduction is the lysogenic cycle. Though often skipped by many types of viruses, this phase is often involved in the replication of quite a few deadly viruses like HIV.

In this cycle, the whole or part of the viral genome is incorporated into the host cell genome. At each subsequent division, the viral-original genetic material is replicated. This allows the virus to infect more and more cells just by the normal mechanism of cell division.

The advantages of this phase is that by entering the host cell and fusing with the host DNA, the host cell functions as well as before the infection, meaning that the viral genome is propagated with each division for the whole length of the cell's lifespan.

Another advantage (Only for hosts with immune systems of some kind) is that by incorporation in the host cell DNA, the only way to remove the virus part of it is to kill the cell. Not only that, since the cells are functioning normally, there is virtually no way to differentiate the infected cells from the normal cells. This means that the virus can remain in the body for a very long time until the correct trigger is supplied.

The next phase of viral reproduction the lytic cycle. The lytic cycle is typically considered the main method of viral replication, since it results in the destruction of the infected cell.

Viruses of the lytic cycle are called virulent viruses. The lytic cycle is a six-stage cycle, called the virus replication cycle. In the first stage, called "penetration", the virus injects its own nucleic acids into a host cell. Then the viral acid form a circle in the center of the cell. Different viruses have different ways to trick the host cell ribosomes to read them instead of the host cell genome. at the end of the cycle, the number of viruses inside becomes too much for the cell to hold, the membrane splits and the viruses are free to infect other cells.

Here is a video to illustrate both phases.