Although published data regarding relative target cell densities in the penis have been conflicting to date (discussed in further detail below), the mere presence of a greater epithelial surface containing a greater absolute number of cells might provide enough of a selective advantage for the virus. This phenomenon may also contribute to the decreased efficiency of female-to-male
HIV transmission relative to either male-to-female or male-to-male routes of sexual transmission.10,11 Once it became clear that male circumcision could reduce HIV transmission to men, additional studies originating from the African circumcision trials were undertaken to determine whether the prevalence of other sexually transmitted infections (STIs)
were affected. Two groups showed that prevalence rates for human papillomavirus infections were significantly lower in circumcised men over a 2-year period.12,13 However, both studies selleck products were limited by the inclusion of only two time points or samples collected per subject. In addition, the collection method employed by both groups (superficial swabs of either the urethra or coronal sulcus) could not control for contamination from recent sexual partners. Tobian et al. also reported decreased herpes simplex virus type 2 (HSV-2) incidence rates among circumcised men, as determined by HSV-2 serologies. In contrast, male circumcision had no effect on either Treponema pallidum (syphilis) or Neisseria gonorrhoeae infection rates. Similarly, a report from Kenya saw no effect in prevalence selleckchem rates of either Trichomonas vaginalis, Chlamydia trachomatis, or N. gonorrhoeae infections after male circumcision.14 The reason for the disparity seen between the effect of male circumcision on viral and bacterial pathogens is not entirely clear, but likely relate to differences in routes taken during transmission (i.e., the squamous epithelia
found in foreskin, glans, and shaft tissue versus the columnar epithelium of the urethra). In addition to infectious pathogens, male circumcision might also affect commensal bacteria that naturally colonize the penile surface. To study this, the Ugandan group swabbed the coronal sulci of 12 HIV-seronegative men both before and 12 months after circumcision.15 Using Idoxuridine 16S rRNA sequencing, Price et al. reported that different bacterial families were found after circumcision. Anaerobic bacterial species, some associated with bacterial vaginosis in women, were found in greater abundance on the uncircumcised penile surface. How exactly the type of bacteria found on the surface relates to HIV transmission is unknown; one possibility is that the microbiological shift away from an anaerobic environment after circumcision decreases nascent inflammation and thereby reduces the likelihood that an invading HIV particle would encounter an immune cell to initiate infection.