Why Does Circumcision Reduce HIV Risk?

Why Does Circumcision Reduce HIV Risk?
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Circumcision greatly alters the microbiome of the human penis, reducing the total number and diversity of bacteria. Researchers speculate this change could help explain why circumcised men are less likely to acquire HIV.

Scientists report in the American Society for Microbiology’s journal mBio on a clinical trial conducted with 156 men from Uganda. The subjects were randomly assigned to either a control or intervention group, the latter receiving circumcision. The microbiome from each subject’s coronal sulcus (the small furrow immediately beneath the “head” of the penis) was sampled upon enrollment and at follow-up one year later.

By sequencing the 16S rDNA in the samples, the researchers were able to identify the types of bacteria present. Additionally, they used the same molecule to estimate the bacterial load.

After one year, the circumcised men had significantly fewer bacteria than those who remained uncircumcised. Specifically, there was a marked decrease in the number of anaerobes.

“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,” says corresponding author Lance Price in a statement.

Circumcision Reduces Risk of HIV Infection

In men, circumcision lowers the risk of acquiring sexually transmitted viral infections. For HIV, that risk falls by 50-60 percent. But why this occurs is unknown.

It is thought that the foreskin in uncircumcised males is particularly susceptible to HIV. The reason is because the foreskin contains many Langerhans’ cells, a type of dendritic cell, which HIV can readily invade en route to its infection of the body’s T-cells. Thus, removing the foreskin helps block this route of entry.

Price and colleagues also believe that the microbiota plays a role. Bacteria cause inflammation, which recruits immune cells to the site of the infection. But as Price’s team demonstrated, circumcision drastically reduces the number of anaerobes. Perhaps this shift in the microbial flora reduces inflammation, thereby decreasing the number of immune cells available for HIV to hijack.

To Circumcise or Not to Circumcise?

The practice of circumcision has become a hot-button social issue in recent years. Anti-circumcision activists believe that the procedure has little to no medical benefit and is tantamount to male genital mutilation. However, the American Academy of Pediatrics disagrees. Though it does not recommend circumcision for all boys, the Academy believes that the health benefits outweigh the risks.

This may be particularly true in parts of the world with less access to antiretroviral therapy. According to the World Health Organization, in Uganda, where the mBio study was conducted, only 54 percent of people with advanced HIV infection are receiving proper treatment.

So even though some may consider circumcision a primitive technique, it is undoubtedly a useful weapon against the scourge of HIV in the developing world.

Source: Cindy M. Liu et al. "Male Circumcision Significantly Reduces Prevalence and Load of Genital Anaerobic Bacteria." mBio 4 (2): e00076-13. 16-April-2013. doi: 10.1128/​mBio.00076-13

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