A new DNA study found that more than two-thirds of healthy Americans have one or more strains of human papillomavirus (HPV) either in their skin, vagina, mouth, or gut. Interestingly, however, only 4 percent of participants had either of the two strains responsible for most cervical cancers. Most of the HPV infections found were harmless and had no negative impact on health, and based on this study researchers are beginning to question whether different strains of the virus actually keep each other in check the way that “good” and “bad” bacteria are known to do.

Though HPV gets a lot of attention as the most common sexually transmitted infection (the Centers for Disease Control and Prevention estimates 14 million new infections per year), there are 148 strains of HPV that have been discovered thus far and only 40 of them are known to infect the genitals. Two of these strains, 6 and 11, are responsible for most cases of genital warts, and another two, strains 16 and 18, are known to be responsible for 70 percent of cervical cancers. Other strains, however, focus on different body parts. There are some, for example, that are known to cause warts on the neck or face, while some are responsible for plantar warts on the bottom of the feet. Many HPV infections, however, carry little health risk and, in some cases, the body is able to rid itself of the virus.

In an effort to better understand the extent of HPV in the human body and its effect on health, researchers at New York University’s Langone Medical Center analyzed DNA samples collected as part of the National Institutes of Health’s (NIH) Human Microbiome Project. The results found that 71 of the 103 participants had HPV, but only four had the strains known to cause cervical cancer. In total, researchers found 109 strains of the virus. Most study participants had HPV infections in the skin (61 percent) followed by the vagina (41 percent), the mouth (30 percent), and the gut (17 percent).

Taking a closer look, researchers found that skin samples included 80 strains of HPV, 40 of which were only found in skin. They found 43 types of HPV in vaginal tissues, 20 of which were only found there. The mouth samples contained 33 types of the virus, five of which were exclusively oral. As for the gut, they found six strains of HPV there, but all of those strains were also found in other organs.

Zhiheng Pei, a pathologist who was one of the authors of this study, said the findings suggest that current screening tests, which are limited to about a dozen strains of the virus, are inadequate. He added that “broader detection methods and comprehensive diagnostic tests are needed to more accurately assess people’s ‘true’ HPV infection status.” That said, Pei cautions that people should not overreact to these findings “until the harm or benefit of most of these strains becomes apparent.”

These findings also lay the ground work for the idea that infection with multiple strains of HPV may have benefits. Pei explained, “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.” Co-author Yingfei Mai added, “The HPV ‘community’ in healthy people is surprisingly more vast and complex than previously thought, and much further monitoring and research is needed to determine how the various non-cancer-causing HPV genotypes interact with the cancer-causing strains, such as genotypes 16 and 18, and what causes these strains to trigger cancer.”

In the meantime, the authors believe that people should take advantage of the available HPV vaccines, both of which cover strains 16 and 18 and one of which also covers the two strains known to cause genital warts. Their hope is that this research can be the basis for a broader vaccine that will cover HPV infection in other parts of the body as well. The researchers are also working to develop new screening tests that can detect additional strains of the virus.