Life Cycle
The human papillomavirus (also known as HPV) has a distinct life cycle that allows it to only be transferred from one host to the next at certain times. Once the virus has infected a cell, it can go into one of two different modes. During one mode, which is called dormancy, the virus simply hides inside the cell. Because during dormancy the virus is not actively replicating, it does not cause any cellular changes that alert the immune system that a virus has infected the cell. This allows the virus to stay in the cell for an extended period of time (often several years) undetected. The other mode for the virus is an active infection. At this point the virus will take over the cell's internal machinery and resources to make additional copies of the virus. When the cell has made enough copies of the virus, the virus will cause the cell to rupture, allowing the copies of the virus to spread. It is during this period that the human papillomavirus can be transferred from one person to the next.
Transfer
When the virus is actively replicating, it can be spread as a result of direct skin-to-skin contact between an infected individual and an uninfected person. The virus will typically actively replicate on the skin cells and can cause the cells to fall off the body (a process known as shedding). Often times this results in a wart being formed, although some strains of HPV do not cause any warts. Whenever the human papillomavirus is actively replicating on the skin, it can be transmitted. Certain strains of human papillomavirus are often transmitted sexually, causing HPV to sometimes be referred to as a sexually transmitted disease.
Transmission Prevention
The best way to prevent human papillomavirus from being transferred from an infected individual to an infected one is for the uninfected person to avoid skin-to-skin contact with people with actively replicating infections (which can be difficult because not all strains cause visible skin lesions). In the case of HPV strains that can be transmitted sexually, a condom (or other barrier methods) may not be enough to prevent transmission. Because some strains of HPV can lead to an increased risk of cervical cancer, a vaccine has been created for these "high-risk" strains. Women who are vaccinated against these high-risk strains are protected from infection (but only for these strains).
