Human papilloma viruses (HPV) comprise a large number of genetically related viruses. Quite a few of these viruses are known to cause warts, such as the ones commonly found on the skin. There is one more group of HPV that particularly infect the mucosal surfaces of the genitals, including penis, vagina, vulva, and cervix. These viruses are spread among adults during sexual activity. A particular group of HPV that infect the genitals causes soft warts, termed as condyloma acuminata and though they are quite common, they could sometimes even become cancerous.
Common among the low-risk HPV are designated HPV 6 and 11. There is a second group of viruses, termed as high-risk HPV, which often gives rise to cervical cancer. Women infected with these viruses are at a high risk of developing precancerous lesions. In most of the cases, infection due to these viruses is common in adolescents or women who are in their 20s, but most of the time they do not result in cancerous growth. The most common high-risk HPV is type 16. The appearance of abnormal cells containing high-risk HPV types is seen most frequently in women above the age of 30 who have produced abnormal pap smear results.
Some time or the other in their lives, more than 75 per cent of the population has been infected with HPV, making it the commonest of all sexually transmitted diseases. HPV infections are, however, not known to cause obvious symptoms of sexual transmission. According to surveys, while genital warts will occur in 1 or 2 of every 100 persons, abnormal pap smears with atypical cells due to HPV can occur in about 2-5 per cent of women. If not treated, such women are at higher risk of developing cervical cancer. Almost all cases of cervical cancer involve high-risk HPV types. It is believed that most cervical cancers take about five years to develop from early cellular changes into an invasive, life-threatening cervical cancer. It is not fully understood why most infections with high-risk HPV are of short duration, though a small percentage persist and eventually transform cervical cells into a state of cancerous growth.
Seeing the link between HPV, precancerous cellular changes and cervical cancer, it is often suggested that testing for HPV can be a useful addition to pap smears which involve microscopic analysis of cells removed from the cervix.