Via PBS NewsHour, a must-read: How vaginal bacteria could be stoking HIV cases and blocking prevention. After explaining how a vaginal biome dominated by Lactobacillus confers protection against HIV, the report continues:
The problem is that Lactobacillus doesn’t dominate the microbiomes of many of the world’s women — especially women most at risk for HIV. A 2010 study of American women in the Proceedings of the National Academy of Sciences found that Lactobacillus dominated the microbiomes of Asian and white women, but accounted for only 59.6 and 61.9 percent of the microbiomes of Latina and Black women, respectively. The same has been found in sub-Saharan Africa.
That diversity in the microbiome, and the associated higher pH and increased inflammation is part of what we call BV.
Saying someone has BV is as specific as saying that someone has a cold. Yes, BV is associated with specific symptoms, such as watery discharge and malodor. But only specific combinations of bacteria are associated with those symptoms. So it’s possible to have asymptomatic BV — that is, diversity in the microbiome that increases pH but doesn’t cause discharge or odor. And it’s possible to have those symptoms and be so used to them that they don’t strike you as abnormal, or cause you to visit a doctor for treatment.
“Women don’t come in,” said David Fredricks, member of the Vaccine and Infectious Disease Division of the Fred Hutchinson Cancer Research Center and author of that 2005 NEJM article, “and say, ‘My pH is off.’ They say, ‘I have malodor’ or ‘I have discharge.’”
But that’s exactly what’s happening, especially in women at high risk for HIV. In the U.S., the overall BV rate hovers around 29 percent. But for African American women, whose rates of HIV are 20 times higher than their white counterparts, BV rates can be as high as 51 percent. In Cape Town, where four in 10 new HIV infections occur among women 15 to 24, rates of BV reach 47 percent. And more than two-thirds of those women report no symptoms, said Shaun Barnabas, a PhD candidate studying the vaginal microbiome in Cape Town.
Finding the Smoking Gun
And it turns out that none of the bacteria associated with the symptoms of BV are the ones associated with HIV risk. For that, you have to turn to one strain: Prevotella bivia.
At least that’s the finding of a study released today at the International AIDS Conference. The study, based on the sequencing and analysis of the microbiomes of 120 South African women, found that it was only women with P. bivia in their microbiome who also were statistically more likely to have HIV, too—by a lot.
“What we found,” said CAPRISA’s Karim, “was that if a woman had ever had Prevotella, she had an almost 20-fold higher risk for inflammation and HIV acquisition than other women.”
Of the 120 women studied, 10 percent had ever had Prevotella. But that 10 percent accounted for 41 percent of all infections. That means that two out of five women in the study had acquired HIV because P. bivia set the stage.