Human papillomaviruses (HPV) are small double-stranded DNA viruses which infect certain layers of cells which protect tissues against chemicals and physical tear. These layers of cells are known as stratified epithelium. There are at least 200 different types of HPV, which can be divided into those infecting cutaneous or upper surfaces of tissues and those infecting mucosal or inner surfaces of tissues.
While the viruses often cause low risk or benign proliferative lesions like warts, there is a subgroup of viruses which cause high risk or pre-cancerous and cancerous lesions which occur most frequently in the genital tract. Cancer of the cervix is by far the most common cancer.
A Brief History of Viruses and Cancer
In the 1900s the only known cause of human cancer were environmental carcinogens such as radium or organic chemicals such as paraffin and dye by-products, that were known to cause solid tumours. In the late 18th century, an English surgeon named Percivall Pott had argued that cancer of the scrotum, endemic among chimney sweeps, was caused by chronic exposure to chimney soot and smoke.
These observations led to a theory called the somatic mutation hypothesis of cancer. But the precise nature of cell alteration was unknown.
In 1910, a chicken virologist named Peyton Rous injected a spindle cell sarcoma ( a type of cancer) from a sick chicken to another and found that cancer could be transmitted from one chicken to another. Rous concluded that the agent responsible for carrying this type of cancer was not a cell or an environmental carcinogen but some tiny particle lurking within a cell. After further study, he concluded that the only biological agent that had the properties in his study was a virus. His virus was later called Rous Sarcoma Virus, or RSV.
In 1940 another virologist - Rous colleague- named Richard Schope reported a papilloma Virus that caused wartlike tumours in rabbits.
In 1958, an Irish surgeon, Denis Burkit discovered an aggressive form of lymphoma that occurred endemically among children in Uganda. The pattern of distribution suggested an infectious cause. The Lymphoma is now called Burkitt's Lymphoma. When some British virologists analyzed the lymphoma cells, they discovered an infectious virus which was later named Epstein - Barr Virus (EBV).
These historical discoveries led to aggressive laboratory studies to connect the relationship between viral carcinogens and alteration of cell DNA to the proliferation of cancer cells in a human body.
HPV Aggressively Infect the cells, alter cellular DNA and change how cells replicate.
The HPV enters the layers of cells known as epithelium and infects these epithelial cells where they maintain a copy number of 50–100 genomes per cell. Upon cell division, one daughter cell will remain part of the basal epithelium, while the other daughter cell will migrate up to the next level and starts to differentiate and infect other cells.
HPV Infection is a Sexually Transmitted Infection ( STI).
Approximately 75% of sexually active people will have at least one HPV infection in their lifetime, with the highest rates of HPV infection occurring in young people aged 15 to 24.
HPV is the most common sexually transmitted infection. As discussed above, HPV is usually harmless and goes away by itself, but some types can lead to cancer or genital warts.
HPV types 16 and 18 lead to the majority of cancer cases. These viruses are called high-risk HPV. Cervical cancer is most commonly linked to HPV, but HPV can also cause cancer in the vulva, vagina, penis, anus, mouth, and throat.
HPV types 6 and 11 are considered low - risk HPV because they don't lead to cancer. However, they cause genital warts and other common warts like hand warts and plantar warts on the feet. These viruses aren’t sexually transmitted.
Genital HPV infections are very, very common. In fact, most people who have sex get these viruses at some point in their lives. HPV can also be transmitted through other intimate contact including genital rubbing.
Most people with HPV have no symptoms and feel totally fine, so they usually don’t even know they’re infected. It’s estimated that 72 percent of throat cancers in men, and 91 percent of cervical cancers in women are caused by HPV.
HPV can be passed even when an infected person has no signs or symptoms.
Anyone who is sexually active can get HPV, even if they had sex with only one person. Symptoms can also develop years after a sexual encounter with someone who is infected. This makes it hard to know when one first became infected.
Most genital HPV infections aren’t harmful and go away on their own.
Condoms can help prevent the spread of HPV, but they do not provide full protection.
Shaving the genital area can promote the spread of genital warts.
Vaccine. The most up-to-date vaccine provides protection against 7 HPV types associated with 90% of penis and cervical cancers.
World wide, HPV vaccination is approved for females from ages 9 – 45 and males from ages 9 – 26.
Vaccination works best before one is sexually active or have already become infected or exposed to an HPV virus. The vaccine can help reduce the risk of HPV-related disease at any time, even after an abnormal test from cancer screening.