MEXICO CITY – When you think of factors associated with increased risks of acquiring HIV, big pictures of marginalization, discrimination, geographic location, economic inequities and gender inequality might come to mind. With two maps here on Tuesday, a scientist zeroed in on a factor that, while literally microscopic, can also make a great difference: bacteria.
On one map presented by microbiologist Adam Burgener of the University of Manitoba, an overlay highlighted the places with the greatest prevalence of HIV. The other, with close to the same regions highlighted, showed where rates of vaginal dysbiosis – imbalances in the community of bacteria, viruses, fungi and other microorganisms that naturally live in the vagina, known as the vaginal microbiome – are highest. The maps provided a large-scale illustration of the presentation’s central point: how variations in the microbiome can both put women at higher risk of HIV infection and accelerate the progression of disease.
In an era of accelerated understanding of HIV dynamics, scientists are just beginning to scratch the surface of how colonies of microbes in the gut, vagina and other places in the body can affect human health and be associated with a range of illnesses and chronic conditions that include cervical cancer, diabetes, heart disease – and HIV.
While some bacteria work to clear pathogenic organisms, others can cause changes in the body that allow HIV and other viruses to more easily establish infection, Burgener said. Imbalances in the gut microbiome, for example, can deplete bacteria that metabolize vitamins and work to improve the immune system while increasing bacteria that cause inflammation, a major factor in HIV infection and disease progression.
“There are many bacteria linked to biomarkers of HIV disease progression,” Burgener said. “Men who have sex with men engage in sexual behavior that result in higher levels of prevotella – a bacteria associated with increased inflammation,” he said.
Women with high levels of bacterial vaginosis — an overgrowth of bacteria which results from imbalances of the vaginal microbiome — experience increased inflammation in the vagina, which leads to barrier damage, making it easier for HIV to enter the body and establish infection, Burgener said.
Studies of the microbiome in African women show high levels of bacterial vaginosis among women in Tanzania, Rwanda and South Africa, among others – all places with high rates of HIV infection, he said.
“Bacterial vaginosis is associated with a 60 percent increased risk of acquiring HIV,” he said.
Burgener’s lab worked with the CAPRISA 004 trial, which tested a vaginal microbicide, or a topical gel containing an HIV drug to protect against HIV and found that the product worked three times better in women without imbalances in the vaginal microbiome, suggesting that the vaginal microbiome can impact topical HIV prevention strategies, he said. Follow-up studies showed the vaginal microbiome has no impact on the efficacy of oral pre-exposure prophylaxis to prevent HIV.
Treatments to address bacterial vaginosis and other factors that increase vaginal inflammation are lacking, Burgener said. Standard therapies for bacteria like antibiotic treatment do not have durable effectiveness and have high recurrence rates, he said, and “do not resolve genital inflammation features associated with HIV acquisition risk,” he said.
More research of the microbiome is needed to come up with ways to address inflammation and other issues, Burgener said. “We want to better understand what functional components affect genital inflammation and how does this relate to HIV infection in order to help devise better interventions,” he said.
It’s the tiny things that add up, he said. “There are 10 times more microbial cells in the human body than human cells,” Burgener said. Together he added, “bacterial cells weigh as much as your liver.”