Hidden strains of HPV found in 'virus-negative' genital warts

There are 170 established HPV types. Cancerous human papillomavirus (HPV) viruses are the main cause of cervical cancer, and are found in close to 100% of cervical tumors.

Cervical cancer and genital warts are caused by HPV. However, testing for the virus using standard techniques can sometimes give a negative result - in these cases, the condylomas are called 'virus-negative' warts.

In a new study published in Virology, researchers assessed the DNA found in samples taken from 40 patients with 'virus-negative' genital warts. Through a general DNA sequencing approach, the researchers showed that several of the negative samples did in fact contain HPV DNA.

This means that virus-negative warts can harbor small amounts of more distantly related viruses that escaped previous detection. According to the research, there is a diverse pool of previously unknown HPV types that infect humans and are detectable on genital warts.

The findings have implications for the knowledge of diversity of HPV types, as these viruses are currently undetectable using traditional testing methods.

Ten pools of four samples taken from virus-negative warts were tested using genetic material straight from the patient - including viral, bacterial and human DNA. Five of the pools contained HPV, and three of these contained new strains of the virus.

There are more than 100 types of HPV. About 30 or so types can cause genital infections. Some can cause genital warts; other types can cause cervical or other genital cancers. The other 70 or so HPV types can cause infections and warts elsewhere on the body, such as on the hands.

Many sexually active women and men will contract HPV at some point in their lifetime. Most will never even know it. Usually, this virus does not cause any symptoms and doesn't cause disease. Often, the body can clear HPV infection on its own within two years or less.

Some types of HPV, typically HPV 6 and HPV 11, cause genital warts. The warts are rarely associated with cervical cancers. They are considered "low-risk" HPV.
HPV and Cervical Cancer

Certain HPV types are classified as "high-risk" because they lead to abnormal cell changes and can cause genital cancers: cervical cancer as well as cancer of the vulva, anus, and penis. In fact, researchers say that virtually all cervical cancers - more than 99% - are caused by these high-risk HPV viruses. The most common of the high-risk strains of HPV are types 16 and 18, which cause about 70% of all cervical cancers.

If the body clears the infection, the cervical cells return to normal. But if the body doesn't clear the infection, the cells in the cervix can continue to change abnormally. This can lead to precancerous changes or cervical cancer.

Rates of Cervical Cancer