The composition of the vaginal microflora affects the viral load within the vaginal secretions of HIV-positive women, according to a late-breaking abstract presented on Monday at the Fifteenth Conference on Retroviruses and Opportunistic Infections in Boston.
Lead author Jane Hitti of the University of Washington at Seattle said that about 50% of the women studied at any time had hydrogen peroxide-producing (H2O2+) Lactobacillus, which is found in the microflora of a healthy vagina. The change in vaginal microflora seen in bacterial vaginosis, and especially the loss of H2O2+ Lactobacillus, is associated with increased risk of HIV infection.
There is a dynamic relationship between the Lactobacillus and the bacteria that cause bacterial vaginosis, Hitti said. BV-associated bacteria appear to actively increase HIV replication while the H2O2+-producing bacteria inhibit it.
In a prospective, observational cohort study, which assessed the effect over time of H2O2+ Lactobacillus colonisation on HIV viral load in vaginal secretions, women whose bacterial microflora switched from those cause BV to those Lactobacillus experienced a 0.7 log (fivefold) drop in the HIV viral load in vaginal secretions (cervico-vaginal lavage or CVL). Conversely, a switch from Lactobacillus to BV bacteria signalled a 0.5 log (threefold) increase in CVL viral load.
For the study, 57 HIV-1-infected women from Seattle and from Rochester, NY were recruited and followed every three to four months for a median of six visits per woman (range one to 15 visits, with four in the first year and three a year thereafter). At each visit, plasma and CVL viral loads were determined, and cultures to identify H2O2+ Lactobacillus and BV bacteria were performed and the women were also tested for gonorrhoea, trichomoniasis and chlamydia.
At the start of the study, 31 (54%) women were on antiretroviral therapy and 22 (39%) had an undetectable viral load (<30 copies/mL). Lactobacillus was present in 32 women, 18% of whom had clinical signs of BV; it was absent in 25 women, 47% of whom had clinical BV.
During the study, blood viral load was detectable at 64% of visits and CVL viral load was detectable (>1500 copies/mL) at 17% of visits; CVL viral load was highly correlated with plasma viral load (p<0.001), but not antiretroviral therapy (p<0.78).
The presence of H2O2+-producing bacteria was in itself associated with a threefold reduction in CVL viral load (p = <0.01) and BV bacteria with a 60% increase (p= 0.015). Trichomonas was also associated with a threefold increase in viral load but because infections were less common, this was not statistically significant.
The data yielded 270 visit pairs suitable for analysis of changes in microflora. Colonisation by H2O2+ Lactobacillus was dynamic over time. While almost half, 121 (47%), of visit pairs had stable colonisation between visits, 39 (15%) visit pairs reported the appearance of the bacterium between visits. A similar number, 36 (14%) visit pairs, reported the loss of the bacterium between visits, and 62 (24%) showed no evidence of colonisation at either visit.
As described above, appearance of the H2O2+ Lactobacillus between visits was associated with a 0.7 log10 decrease in CVL viral load (p = 0.015), and loss of the bacterium resulted in a 0.5 log10 increase in CVL viral load (p = 0.029) when compared with stable colonisation. All results were adjusted for changes in plasma viral load and antiretroviral therapy status, but not for herpes (HSV-2) status or shedding – one limitation of the study.
When clinical BV was present, women were treated for it, but Hitti commented that treating BV got rid of the associated bacteria but was not necessarily associated with the reappearance of Lactobacillus.
Hitti commented that these changes in CVL viral load associated with changes in vaginal microflora might one day inform positive prevention strategies for HIV-positive women. She said “If a probiotic replacement proves to be effective this could be an important strategy.”
However, she added, although there had been a few studies to see if supplementation with Lactobacillus formulations could re-establish stable colonisation in HIV-negative women, she was unaware of any studies done in HIV-positive women, and hoped funding would be forthcoming for one.
Asked to comment on women possibly trying over-the-counter supplements, Hitti commented that the vaginal Lactobacillus was “a cousin” of those found in yoghurt and derived supplements and would not necessarily have the same H2O2+-secreting properties or effect on HIV.