Increase in Oral Sex Practices May Lead to Chlamydia-Associated Female Infertility

Investigators from the University of Maryland School of Dentistry (UMSOD) are urging scientists to consider a new hypothesis regarding the most frequently reported bacterial genital infectious disease in women in the United States: chlamydia.

Because of an increase in oral sex practices, investigators are urging scientists and clinicians to consider that when transmitted via the fecal-oral or genital-oral route, Chlamydia trachomatis (C. trachomatis) can colonize the gastrointestinal tract (GIT), and ultimately, increase risks of female infertility. The UMD investigators explain the new paradigm in an article published in The Journal of Infectious Diseases.

One of the most common sexually transmitted diseases around the world, chlamydia infections often go unnoticed for years as infected individuals often do not present with symptoms. This increases the likelihood that infected individuals will not receive the treatment to cure the infection; if left uncured, chlamydia can result in urethritis, cervicitis, pelvic inflammatory disease, ectopic pregnancy, and infertility, according to the University of Maryland, Baltimore, press release on the study.

The investigators hypothesize 3 central points in their paper:

1. All members of the Chlamydiaceae have evolved primarily as commensals of the digestive tract of their host(s) with fecal-oral transmission (FOT) as the principal route of dissemination to new hosts. In communities where FOT is reduced, the occurrence of chlamydiae in the digestive tract is reduced.
2. C. trachomatis, a commensal microorganism of the human GIT, is an opportunistic pathogen in the genital and respiratory tracts and the conjunctiva. Under conditions of reduced FOT, direct contact is the primary mode of transmission.
3. C. trachomatis is efficiently transmitted to the GIT of new hosts via oral sex. The increasing practice of oral sex is contributing to the increased prevalence of C. trachomatis in the human GIT in communities where FOT was previously reduced.

As for what inspired the researchers to develop this hypothesis, Contagion^® spoke with lead author and chair of the Department of Microbial Pathogenesis at the University of Maryland School of Dentistry Patrik Bavoil, PhD. "It simply made less and less sense that Chlamydia trachomatis, the species that causes oculo-genital infection in humans, would be so different from its veterinary cousins. Evidence kept accumulating that the Chlamydia species that cause infection and disease in animals are first and foremost colonizers of the digestive tract of their host and are completely asymptomatic while there. They only cause disease opportunistically when they get out of their 'home' in the gut. Why would C. trachomatis be different? That was the initial question that fueled the hypothesis," Dr. Bavoil explained.

"Credit is due to the group of Roger Rank and Laxmi Yeruva at the University of Arkansas who developed the idea that gut chlamydiae could be the basis for chlamydial persistence, or the ability of chlamydia to 'disappear' and subsequently reappear sometimes years later without an apparent source of reinfection. These observations, plus historical and current evidence for a missing reservoir for trachoma, growing evidence for a missing source of infection in urogenital chlamydial infection (e.g. women with rectal infection who report practicing oral sex but no anal sex) are all compelling arguments that converge to form the hypothesis," he added.

In their article, the authors note that when transmitted via fecal-oral or genital-oral routes, the pathogen may colonize GIT without symptoms.

“An indirect but compelling argument that supports the idea that C. trachomatis colonizes the GIT without clinical disease is that most, if not all, other Chlamydia species are first and foremost innocuous gut commensals,” the authors write. C. trachomatis that colonizes GI sites in humans could “disseminate chronically or episodically to the rectum or feces,” according to the press release. Rectal C. trachomatis can, in turn, either chronically or episodically infect the female lower genital tract, “exacerbating host responses and contributing to reproductive sequelae.”

Another important point that the investigators make is the impact that modern sanitation and enhanced personal hygiene have had on the disease. "At the end of the industrial revolution, rigorous sanitation that put human waste underground (in septic fields or sewerage systems) effectively curtailed the spread of many infectious agents that were previously naturally transmitted via FOT," Dr. Bavoil said. "The River Thames in London used to be the city’s only sewerage system and London had multiple cholera outbreaks as a result. When London and other large European cities acquired sewerage systems (many can be visited today), cholera and many other infections transmitted via FOT disappeared. We hypothesize that C. trachomatis was one of the infectious agents whose transmission via FOT was dramatically reduced upon the advent of sanitation. Personal hygiene acted as a complement to sanitation."

Additionally, the authors also hypothesize that during what they refer to as the “pre-sexual revolution,” a time when practicing oral sex was not as common as it is today, commensal C. trachomatis was probably significantly reduced from human gut microbiota.

“Active oral sex will potentially introduce infectious C. trachomatis directly into the oral cavity and to the oro-nasopharynx, just like FOT did prior to sanitation," Dr. Bavoil explained. "The only differences are the source and the vector: respectively, feces and contaminated fingers/food/water/flies in the case of FOT or fecal-ocular transmission (in the case of trachoma), and contaminated/infected male genitalia and active oral sex in the case of genital-oral transmission from a man to a woman."

Today, the authors estimate that about 75% of women report having had engaged in oral sex. The authors attribute its growing popularity to the common misconception that oral sex is relatively safe compared with sexual intercourse, which requires a condom for protection. The authors stress that this sexual practice poses other risks, like potential female infertility.

"We hypothesize that when the female lower genital tract (LGT) is repeatedly exposed to infectious C. trachomatis via recto-vaginal contamination (the same way a woman acquires UTI from E. coli residing in the gut), it will be subjected to repeated episodes of inflammation that will chronically exacerbate disease," Dr. Bavoil explained. "We also hypothesize that rectal C. trachomatis may cause infection of the female LGT which may ascend to the upper genital tract and cause scarring in the tubes. Tubal damage is the primary cause of female infertility and ectopic pregnancies, the major sequelae of chlamydial infection in humans."

The researchers call on other researchers and clinicians in the field to expand chlamydia screening practices to also sampling rectal sites, and pharyngeal sites when deemed appropriate so that the infection is caught and patients receive treatment, thereby avoiding the potential long-term effects of an undiagnosed infection.

"The hypothesis represents a paradigm shift in chlamydial biology. Researchers need to start thinking about chlamydia, not as a strict pathogen, but as a regular inhabitant of the GIT that only causes problems when taken out of its element, so to speak," Dr. Bavoil said. "This has significant implications both in basic research and in how we deal with chlamydial infections in the clinics or doctor’s office."