Now certain viruses such as HIV do not contain DNA, they contain RNA and they also contain special types of enzymes known as reverse transcriptase. And these enzymes basically reverse transcribe the RNA into DNA and then that DNA is integrated, is incorporated into the host cell genome, the host cell DNA. Now once integrated into our DNA of the host, the cell can basically live on and show no sign of actual infection. And this stage, this phase is known as the doorman period. Now of course eventually we can have some type of environmental factor that can cause the cell to basically undergo the Litig cycle. For example, UV radiation is one form of environmental factor that can basically take a cell under the lythogenic cycle and transform it into the lytic cycle, forced it to go into the lytic cycle and produce many different viruses and eventually lice.