Circumcision and HIV risk: Bacteria may play key role, study finds

April 17, 2013 | by Tami Dennis

Circumcision reduces a man’s risk of HIV infection, scientists have said, although they didn’t exactly understand the “why” behind the link. Now researchers think they know.

Reducing the bacteria on the surface of the penis appears to reduce the liklihood that HIV, shown here in the bloodstream, will take hold, researchers find. Reducing the bacteria on the surface of the penis appears to reduce the likelihood that HIV, shown here in the bloodstream, will take hold, researchers find.

It comes down to microbes. Specifically, removing the foreskin leads to a dramatic reduction in overall bacteria, including anaerobic bacteria, on the penis. Such bacteria can prevent so-called Langerhans cells in the foreskin from fighting off viruses, also leading to inflammation that prompts the body’s immune system to send T4 cells to the scene. These cells can then become infected with HIV.

The findings, published April 16 in the journal mBio, amount to an “aha” moment.

"The bacterial changes identified in this study may play an important role in the HIV risk reduction conferred by male circumcision. Decreasing the load of specific anaerobes could reduce HIV target cell recruitment to the foreskin," the authors wrote.

Their research on the so-called penis microbiome  has led the researchers to make broader ecological comparisons.

"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," said corresponding author Lance Price in a press release from the American Society of for Microbiology, which publishes mBio.

The study’s first author, pathologist Cindy Liu at Translational Genomics Research Institute in Flagstaff, Ariz., summed up her findings this way to the L.A. Times: "It's the same as if you clear-cut a forest. … The community of animals that once lived in that forest is going to change."

As for clinicians, they appear to welcome the findings.

Alexandra Levine, M.D. M.A.C.P., chief medical officer at City of Hope, said the study’s authors make a strong case. "This is an important paper in beginning to document what the reason might be," Levine, a nationally recognized expert on blood diseases and HIV/AIDS-related malignancies, told the L.A. Times. "Their data are convincing to me."

But scientific discovery doesn’t stop with an “aha” moment. As the authors themselves noted in their paper, more research is needed.

“Understanding the mechanisms that underlie the benefits of male circumcision could help to identify new intervention strategies for decreasing HIV transmission, applicable to populations with high HIV prevalence where male circumcision is culturally less acceptable."

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