Circumcision reduces HIV risk by changing penis 'biome', says study

A study released Tuesday says that circumcision significantly reduces men's chances of being infected by HIV by changing the mircobiome of the penis. According to a paper in the American Journal of Microbiology, a reduction of the number of anaerobic bacteria present on the penis appears to play a role in reducing the rate of infection.

In the study, researchers from the Translational Genomics Research Institute (TGen) in Flagstaff, Arizona and at George Washington University in Washington, D.C. studied the effect of circumcision on the types of bacteria that live under the foreskin before and after the procedure via swab cultures taken from a large sample group of adult Ugandan men.

By one year after circumcision, the total bacteria population in the area had dropped significantly. Anaerobic bateria, organisms that thrive in conditions with little or no oxygen, particularly declined.

Scientists have shown that circumcision reduces the risk of HIV infection in men by 50 to 60 percent as well as reducing incidences of human papillomavirus and herpes simplex type 2, but the biological processes involved remained a mystery.

It could be, some scientists said, that the anatomy of the circumcised penis makes it less vulnerable to infection. Other scientists argued that the benefits of circumcision are conferred by way of changing the native bacteria population on and around the foreskin. The new study points toward the latter theory.

"There was a dramatic and significant change in the penis microbiome as a result of male circumcision," study author Dr. Lance Price told the website MedicalXpress.com. "From an ecological perspective, it's like rolling back a rock and seeing the ecosystem change. You remove the foreskin and you're increasing the amount of oxygen, decreasing the moisture -- we're changing the ecosystem."

He continued, ""From a public health perspective the findings are really interesting because some of these organisms that are decreasing could cause inflammation. We're used to thinking about how disrupting the gut microbiome can make someone more susceptible to an infection. Now we think maybe this disturbance [in the penile microbiome] could be a good thing - could have a positive effect."

The evidence suggests that high levels of foreskin bacteria could make the body more vulnerable to sexually transmitted viral infections. One theory says that high bacterial loads activate cells in the foreskin called Langerhans cells, which would normally be tasked with defending the body from outside infections. Instead, the cells end up binding with HIV and ferrying it past the body's lines of defense and straight into the system. Reducing the bacterial load on the head of the penis could keep these Langerhans cells from turning traitor.

Price sees the potential in these results for developing non-surgical alternatives to circumcision.

"The work that we're doing, by potentially revealing the underlying biological mechanisms, could reveal alternatives to circumcision that would have the same biological impact. In other words, if we find that it's a group of anaerobes that are increasing the risk for HIV, we can find alternative ways to bring down those anaerobes," he said, thereby decreasing the risk of infection.

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