About two-thirds of healthy American adults are infected with human papillomavirus (HPV), but only a few of the strains they carry are the high-risk types known to cause cancer, new research suggests.
Those high-risk HPV strains – known as types 16 and 18 – cause virtually all cervical cancers, according to the US National Cancer Institute. They also cause most anal cancers and some vaginal, vulvar, penile and oral cancers. However, most infections with high-risk HPVs do not cause cancer, experts note.
Most HPV in skin
For the study, investigators at the NYU Langone Medical Centre in New York City analyzed tissue DNA samples that were collected from four areas – skin, mouth, vagina and gut – of 103 women and men, aged 18 to 80, and stored in a US National Institutes of Health database. The researchers found that 69% of the adults were infected with one or more of 109 of 148 known strains of HPV.
However, only four of the adults had either of the two HPV types known to cause most cases of cervical cancer, some throat cancers and genital warts, according to the study authors.
Most of the HPV infections were detected in the skin (61%), followed by the vagina (41%), mouth (30%) and gut (17%). Of the 71 people infected with HPV, 59% had HPV in one organ, 31% had HPV in two organs, 10% had HPV in three organs, and none had HPV in all four organs.
The greatest number of HPV strains was found in the skin, where there were 80 types of HPV, including 40 found only in the skin. The second highest number of HPV strains was found in the vagina (43 types of HPV, with 20 exclusive to the vagina), followed by the mouth (33 HPV types, with five exclusive to the mouth), and the gut (six types of HPV, all of which were found in other organs).
Vast and complex
The findings show that HPV infection is common and suggest that certain types of HPV may keep others in check and prevent them from spreading out of control, according to the researchers.
"Our study offers initial and broad evidence of a seemingly 'normal' HPV viral biome in people that does not necessarily cause disease and that could very well mimic the highly varied bacterial environment in the body, or microbiome, which is key to maintaining good health," senior study investigator Dr Zhiheng Pei, a pathologist and associate professor, said in a news release from the NYU Langone Medical Centre.
Lead investigator and research scientist Yingfei Ma added that the "HPV 'community' in healthy people is surprisingly more vast and complex than previously thought."
The study was scheduled for presentation at the annual meeting of the American Society for Microbiology in Boston. The data and conclusions should be considered preliminary until published in a peer-reviewed journal.
Ma said in the news release that "much further monitoring and research is needed to determine how the various noncancer-causing HPV genotypes interact with the cancer-causing strains, such as genotypes 16 and 18, and what causes these strains to trigger cancer."
Read: Men need vaccine against anal warts, cancer
Two vaccines approved
Pei pointed out that getting vaccinated against types 16 and 18 is still "a good idea".
The US Food and Drug Administration has approved two HPV vaccines. Gardasil is approved for use in people ages 9 to 26, for the prevention of cervical, anal, vulvar and vaginal cancer, as well as genital warts caused by HPV infection. Cervarix is approved for use in females ages 9 to 25 for the prevention of cervical cancer and precancerous cervical lesions caused by HPV infection. Both vaccines are highly effective in preventing infections with HPV types 16 and 18. Gardasil also prevents infection with HPV types 6 and 11, according to the FDA.
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