February 2nd, 2016
The World Health Organization and the Centers for Disease Control have announced compelling evidence that circumcision reduces the risk of HIV infection in heterosexual men by as much as 60%. However, both organizations emphasize that circumcision is not effective alone in preventing HIV transmission, but should be one component of HIV prevention in addition to safe sex practices, including the use of condoms.
Circumcision has not been shown to reduce risk of HIV infection in men who have sex with men or in women. However, in addition to protection against other sexually transmitted infections, including chlamydia, herpes, syphilis, and human papilloma virus (HPV), circumcision reduces risk in men who are HIV negative and have vaginal sex with women.
The mechanism by which this risk reduction is achieved is at least partially due to the reduction of low oxygen conditions after circumcision. Men who have been circumcised have many fewer microorganisms that survive in conditions of low oxygen and they also have a much lower bacterial load, with as many as 81% fewer bacteria compared to men who have not been circumcised. Experts believe that a high number of bacteria may disturb the body’s immune system by preventing special immune cells, known as Langerhans cells, from activating immune defenses. Langerhans cells usually attach to invading bacteria or viruses and present them to immune system cells to allow the body to develop a healthy immune reaction against these pathogens. When there are a larger number of bacteria, as in men who have not been circumcised, the Langerhans cells may begin to infect healthy cells with the invading microorganisms, instead of simply presenting them to the immune system. In fact, researchers believe that Langerhans cells in uncircumcised men may actually feed HIV directly to healthy immune cells.
Other proposed mechanisms for reduction of HIV transmission after circumcision include the reduction in inflammation from small tears that can occur during intercourse. Tears also allow HIV to enter the bloodstream easily.
The World Health Organization recommends voluntary adult penile circumcision to prevent HIV in countries where there is a heterosexual HIV epidemic, an HIV prevalence over 15%, and a low circumcision rate. Men in other countries will also see a benefit with risk reduction, but it is critical to remember that it, alone, is not adequate to protect men or women from HIV transmission. Circumcision should never be considered a replacement for safe sexual practices and barrier methods of HIV prevention, such as condoms.