The aetiology of bacterial vaginosis

Abstract

Summary Bacterial vaginosis (BV) is the most common vaginal infection among women of childbearing age. This condition is notorious for causing severe complications related to the reproductive health of women. Five decades of intense research established many risk factors for acquisition of BV; however, because of the complexity of BV and lack of a reliable animal model for this condition, its exact aetiology remains elusive. In this manuscript, we use a historical perspective to critically review the development of major theories on the aetiology of BV, ultimately implicating BV‐related pathogens, healthy vaginal microbiota, bacteriophages and the immune response of the host. None of these theories on their own can reliably explain the epidemiological data. Instead, BV is caused by a complex interaction of multiple factors, which include the numerous components of the vaginal microbial ecosystem and their human host. Many of these factors are yet to be characterized because a clear understanding of their relative contribution to the aetiology of BV is pivotal to the formulation of an effective treatment for and prophylaxis of this condition.

The Human Microbiome during Bacterial Vaginosis

“…Qualitative studies using conventional culture methods have characterized over 100 separate phenotypes that can be isolated from the vaginal microbiome, with some phenotypes always being present in high numbers when assessed longitudinally and some phenotypes being present only sporadically, while other phenotypes are consistently present in low numbers (3)(4)(5). It has been shown that certain species of Lactobacillus (Lactobacillus crispatus, L. jensenii, L. gasseri, and L. iners) are more common than others in overtly healthy women, while species of obligately anaerobic rods of the genera Atopobium, Prevotella, Mobiluncus, and Sneathia are more commonly present in women with symptoms of bacterial vaginosis (7)(8)(9)(10)(11)(12)(13). More recent studies using both molecular and advanced culture methods (see below) suggest that what can be considered normal or abnormal occurs on a complex biological spectrum that indicates a greater microbiological diversity for BV than previously thought.…”

Normal flora and bacterial vaginosis in pregnancy: an overview

“…Theoretically, the inception of pregnancy complications as a result of BV is due to its potential to favor ascending infections (from the vagina to the chorioamnion) to cause inflammation of the choriodecidual space and activating pathways of labor and subsequently PTD and PTB (Guerra et al, 2006;Denney and Culhane, 2009;Guédou et al, 2013). BV-related bacteria and the toxins produced by these bacteria can cross the placenta and result in fetal complications (Turovskiy et al, 2011).…”

“…The concept of male-to-female heterosexual transmission is opposed by (i) the treatment of male partners that is not beneficial as it does not result in a decline in BV prevalence and (ii) the fact that there is no solitary etiological agent responsible for BV (Turovskiy et al, 2011).…”

“…The composition of the female reproductive tract makes women two times more likely than men to acquire HIV (Turovskiy et al, 2011). Bacterial vaginosis enhances viral replication and BV-related bacteria directly up-regulate the replication of HIV through a heat-stable HIV-inducing factor Johnson and Lewis, 2008).…”

Assessment of vaginal microbiota in Brazilian women with and without bacterial vaginosis and comparison with Nugent score

“…They also compete with potentially pathogenic bacteria for space and nutrients [4,6,7]. Moreover, healthy vaginal microbiota may also be composed by pathogenic bacteria, such as Gardnerella vaginalis, in low numbers, coexisting in equilibrium with Lactobacillus species [8].…”