The synergy between HSV-2 infection and abnormal vaginal flora has been incrementally exposed. Cross-sectional studies revealed higher prevalences of BV and HSV-2 infection were mutually associated with one another [25
], while longitudinal studies suggested linkage between antecedent HSV-2 infection and incident BV [12
]. Our investigation provides further insight into both phenomena. First, the remarkable persistence of BV in our cohort prior to metronidazole therapy corroborates prior cross-sectional data demonstrating positive reciprocal association between prevalences of BV and HSV-2 infection. In addition, nearly 90% of our study participants had recurrence of BV within a month of completing antimicrobial therapy, a finding consistent with earlier studies that reported increased susceptibility for BV acquisition among HSV-2 infected women. Although based on a small sample size, our study contains findings requisite for better acceptance of a synergism between HSV-2, a persistent viral genital tract infection, and acquisition of pathologic vaginal flora.
Additional studies will be needed to elucidate a biological basis for these resolute shifts to abnormal vaginal flora and high rates of BV recurrence among HSV-2 infected women. Hydrogen peroxide-producing vaginal lactobacilli, thought to provide protection against BV acquisition [27
], are less prevalent among HSV-2 seropositive women [29
], while antecedent HSV-2 infection increases the chance these bacteria are lost from the vagina [13
]. As biologic activity of HSV-2 during latency is limited to reactivation and mucosal shedding, we posit that connections between chronic HSV-2 infection, increased loss of hydrogen peroxide-producing lactobacilli, and increased susceptibility for BV acquisition are sequelae to HSV-2 genital tract shedding. Because this shedding is controlled by genital tract infiltration of HSV-specific CD8+
], we further hypothesize that increased vaginal mucosal inflammation elicited in response to HSV-2 shedding provides linkage between HSV-2 infection and BV recalcitrance. Our findings support these hypotheses as the detection of vaginal leukocytes was associated with greater risk of BV recurrence. It is plausible, therefore, that medications that suppress HSV-2 reactivation will decrease abnormal vaginal flora recurrences or improve efficacies of antimicrobial BV therapies among HSV-2 infected women. In addition to providing the construct for a testable BV prevention strategy, rapid recurrence of BV among HSV-2 seropositive women suggests that similar cohorts will be ideally suited for focused, cost-effective investigation of BV pathogenesis.
Unlike prior studies that reported rapid fluctuation of vaginal microbiota composition and numerous episodes of spontaneously resolving BV [20
], our cohort of HSV-2 seropositive women exhibited a remarkable persistence of BV. Similar to the study design we utilized, these prior investigations asked women to serially self-collect vaginal smears for Gram stain diagnosis of BV. However, our study appears to be the first to identify the HSV-2 serostatus of its participants. This distinction allows us to speculate that rapidly changing vaginal flora compositions and episodes of spontaneously resolving BV may be more frequently seen among investigational cohorts that contain both HSV-2 seronegative and seropositive women. In a prospective study with eligibility criteria similar to our own (inclusion criteria included a vaginal Gram stain score ≥ 7 or a Gram stain score of 4–6 and ≥ 3 Amsel criteria), a 1-month cure rate after metronidazole therapy (400 mg p.o. for 7 days) of 77% and a median time of 176 days until BV recurrence was reported [10
]. Conversely, we detected a 1-month BV cure rate of 11% and a median time of 14 days after treatment until BV recurrence. It is interesting to speculate that our study’s exclusion of HSV-2 seronegative women may have, at least in part, contributed to such highly discrepant results.
Although our study suggests correlation between antecedent HSV-2 infection and vaginal microbiota, it is unable to delineate strength of this association or the mechanisms responsible for results so disparate from prior investigations. We hypothesize increased mucosal tissue inflammation in response to HSV-2 shedding adversely impacts vaginal ecosystems, but are also unable to identify direct connections between HSV-2 shedding and BV acquisition. It seems likely that our inability to form such conclusions is limited by the small number women we enrolled. Enrollment into future investigations will benefit from inclusion of HSV-2 seropositive women with symptomatic or asymptomatic BV as well as a BV positive/HSV-2 seronegative control group. Our conclusions may be further limited by the fact we asked study participants to collect daily vaginal specimens while other BV treatment trials collected specimens at more infrequent (1-month or 3-month) intervals. Thus increased sampling frequency, rather than HSV-2 infection, may be responsible for higher rates of BV recurrence. Our conclusions may also be limited by selection bias and resultant identification of spurious relationships between HSV-2 and BV - the possibility we preferentially enrolled women with factors other than HSV-2 infection that promoted BV recalcitrance. Despite these limitations we provide important new epidemiologic data in support of the synergistic relationships emerging between genital herpes and abnormal vaginal microbiota. Additional work is needed to define mechanisms responsible for this relationship and to determine if vaginal flora health of HSV-2 infected women is improved by medications suppressing genital tract shedding of the virus.