The human vagina is colonized with millions of bacteria18
; at times the microbial community is dominated by a few Lactobacillus
species, and at times, such as in BV, it is characterized by significant diversity.19
We undertook this investigation to assess whether the presence of individual bacterial species was associated with genital HIV-1 RNA and DNA shedding. Lactobacilli have antiinflammatory properties20
and have been linked to decreased HIV-1 genital shedding.21
Conversely, women with abnormal vaginal microbiota have higher levels of inflammatory cytokines22,23
and higher rates of genital HIV-1 shedding.21,24
We found that Lactobacillus
species were associated with less detection of HIV-1 RNA in the genital tract, but found an association between genital HIV-1 RNA and BV-associated species only in women taking ART.
BV has been associated with increased genital proinflammatory cytokines,25
and HIV-1 shedding,21
though this association is not consistent across studies. We suspect that this variation is due to the fact that BV is a clinical syndrome that can differ in terms of microbial composition between women.19
Different species of bacteria have been shown to have different effects: Mycoplasma hominis
has been associated with higher levels, and Lactobacillus
spp. with lower levels of genital HIV-1 RNA.21
has been associated with higher concentrations of vaginal interleukin (IL)-1β26,27
spp. with lower concentrations of IL-8. In our analysis, use of ART modified the association between genital HIV-1 RNA shedding and the presence of vaginal bacteria.
Among women not using ART, we confirmed the suppressive effect of Lactobacillus
species, showing that detection of L. crispatus
is associated with a 35% lower risk of HIV-1 RNA shedding. However, in these women, there was no effect of any BV-associated bacterium on the risk of genital HIV-1 RNA shedding, even after controlling for plasma concentrations of HIV-1 RNA. This may be due to either ongoing replication of virus in the bloodstream, which then passes to the genital secretions via transudation, or due to production of virus from infected cells in the genital tract tissue, which is not impacted by the presence of vaginal bacteria. When viral replication is suppressed by ART, we found that a different Lactobacillus
species (L. jensenii
) was associated with decreased detection of genital HIV-1 RNA, and that two of the seven BV-associated species we tested for increased the likelihood of detecting HIV-1 RNA in genital secretions. This may be due to a transient stimulation of viral expression via activation of NF-κB28
or via other inflammatory pathways. HIV-1 DNA detection in the genital tract was not affected by vaginal bacterial colonization, as we found no association between the presence of any single bacterial species and detection or quantity of HIV-1 DNA.
Our work confirms previous findings that PVL and ART significantly affect the presence and quantity of genital HIV-1 RNA and DNA shedding.29
Systemic treatment of HIV-1 is associated with a decreased risk of transmission to sexual partners,30
likely because of the associated decrease in prevalence and quantity of HIV-1 shedding in genital secretions. In fact, a recent study showed that the quantity of HIV-1 RNA in genital secretions directly correlates with transmission events.3
While antiretroviral treatment reduces HIV-1 transmission, not all patients will qualify for ART, and others shed virus in genital secretions despite successful therapy.1
Thus, understanding the range of factors that contribute to genital shedding of HIV-1 is important.
Many hypothesize that genital tract inflammation has a significant role in promoting HIV-1 shedding.2,31
Genital infections associated with significant inflammation, including gonorrhea, chlamydia, yeast, and herpes, have been associated with increased rates of genital HIV-1 RNA32,33
shedding while treatment of these infections has been associated with a decrease in the detection of HIV-1 in genital secretions.35,36
In this study, the only infection significantly associated with increased HIV-1 RNA shedding was yeast vaginitis. Typically, overgrowth of yeast in the vagina is associated with significant inflammation, which likely mediated HIV-1 RNA shedding either by increasing transudation of plasma virus or by activation of NF-κB to increase transcription of integrated HIV-1 proviruses.28
Surprisingly, we found decreased detection of HIV-1 DNA in women with cervicitis. This could be due to increased apoptosis and destruction of infected cells, or to increased innate antiviral immunity in the area of inflammation. Alternatively, as cervicitis is characterized by a neutrophilic infiltrate, the proportion of T cells in cervicitis samples might be lower, decreasing the likelihood of detecting an HIV-1-infected cell. The paucity of women diagnosed with gonorrhea, chlamydia, or trichomoniasis, three other infections associated with clinical inflammation, limited our ability to evaluate their association with genital HIV-1 shedding.
Recent reports have described a significant difference in genital tract immune activation between women from the United States and Africa.37
Others have shown differences in the composition of the normal vaginal microbiota between healthy white and African-American women, specifically related to decreased colonization with Lactobacillus
In our population, despite similar rates of BV, women enrolled in the United States were more likely to be colonized with L. jensenii,
BVAB1, or BVAB3 than Kenyan women, which may suggest that BV in African women is characterized by different bacterial species than in American women. However, we saw no significant difference in rates of genital tract HIV-1 shedding between U.S. and Kenyan women in this study, after controlling for plasma viral load, suggesting the vaginal factors that mediate HIV-1 shedding are similar.
This study has potential limitations. Our Kenyan participants were enrolled at a single urban clinic and may be a self-selected population. The U.S. women were enrolled in two locations, but were older and more likely to be on ART. Although our participants contributed a large number of visits, the number of individual women is small. Also, given the large number of associations assessed in this analysis, our results should be seen as exploratory and hypothesis-generating. Both yeast vaginitis and cervicitis were defined only by laboratory testing, without regard to clinical symptoms, which may have led to overreporting of these conditions. HIV-1 RNA shedding and genital infections were relatively uncommon in this cohort, which may have limited our ability to detect an association with specific bacteria or infections. Detection of cervicovaginal HIV-1 RNA in Kenyan women, who were unlikely to be using antiretroviral medications, was approximately half as common as rates reported in other African cohorts not receiving treatment.39,40
Our population was relatively healthy, with high CD4 counts and low rates of genital tract infection, which may account for the low rate of genital viral shedding, but may suggest that our results are not generalizable to a wider population. Additionally, we may have missed potential associations with species not tested for; however, the nine species we chose have been highly associated with bacterial vaginosis, which is the clinical syndrome we were hoping to examine.
Our study confirms that systemic factors such as plasma HIV-1 concentrations and use of ART are important determinants of HIV-1 genital shedding. We also showed that certain vaginal bacterial species may be more likely to induce genital shedding of HIV-1 RNA or DNA, especially when viral replication is suppressed by ART. Additionally, we showed that when Lactobacillus species are present, HIV-1 RNA genital shedding was uncommon, whether or not a woman was taking ART. This suggests that promoting a healthy, Lactobacillus-dominant vaginal microbiota may be an important strategy for decreasing the risk of viral shedding and potential transmission.