Humans aren’t the only ones that have to deal with sexually transmitted infections—animals do too. Indeed, chlamydia, syphilis, and several other STIs known all too well among humans have been documented in the animal kingdom with some frequency. Among primates, however, one STI that is unique to humans is gonorrhea. This observation has led some scientists to question why. What gave rise to gonorrhea in humans, but not in other primate species? Some scientists argue that it might have something to do with the fact that humans frequently practice oral sex, a behavior that is rare in non-human primates.

The hypothesis for gonorrhea arising through oral sex is described in a recent commentary published in the Archives of Sexual Behavior. In it, biologist Alan Dixson proposes that gonorrhea originated in the nasopharynx, the area in the back of the throat where the nasal and oral cavities connect. He argues that, in our throats, the bacteria responsible for gonorrhea were relatively harmless; however, when humans began practicing oral sex, these bacteria were transferred to the genitals. Dixson suggests that this is when problems likely arose, because the genital tract just doesn’t tolerate the bacteria as well. In the author's words, genital gonorrhea could potentially be thought of as an “invasive species” from the throat that is capable of wreaking havoc in other areas of the body.

Of course, we don’t know for sure that gonorrhea originated in the throat. What we do know is that gonorrhea infections can take hold in the throat rather easily when oral sex is performed on an infected partner. We also know that additional species of the same bacteria that causes gonorrhea commonly reside in the nasopharynx (most of which are harmless).

In addition, like most of the other species of this bacteria, when gonorrhea infections occur in the throat, it is often the case that they do not cause any symptoms or lead to any serious complications (which would make sense if gonorrhea had been derived from a bacterial precursor in the throat). The major problem with oral gonorrhea infections is that someone who has one can potentially spread it to others’ genitals through oral sex—and it’s really the genital infections that have the potential to lead to the most serious problems, including permanent infertility.

Again, it’s important to keep in mind that this is just a hypothesis, and the author of this article does not present it as anything more than that. Subsequent research and testing will determine whether it is supported. In the meantime, however, it is a fascinating thought because it turns conventional thinking on its head and highlights the potential role that humans’ sexual behaviors might play in the development and spread of STIs.

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To learn more about this research, see: Dixson, A. (in press). Human sexual behavior and the origins of gonorrhea. Archives of Sexual Behavior.

Image Source: Wikimedia Commons/NIAID

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