How Vaginal Microbes Can Help Stop HIV
by Bailey Sasseville
If you were to count all the cells that make up your body, you would find something startling: one hundred million of these cells don’t even belong to you. One hundred million are actually microorganisms living in and on your body, while you claim only about ten million as truly yours. It is perhaps unsurprising, then, that these microbes have a large effect on our health and wellness; yet we still don’t know much about what they actually do. While there are a number of microbes that can invade our bodies and cause disease, many live in our bodies and are either harmless or even beneficial. They help digest our food, process vitamins and minerals, protect against harmful microbes and combat autoimmune diseases. The Human Microbiome Project is attempting to catalog and study the communities of microorganisms living in association with the human body, in an effort to “determine the relationship between diseases and changes in the human microbiome.”
We have begun to discover correlations already: babies who are born through C-section have different microbiomes than those born by vaginal delivery, and are more likely to develop allergies and asthma as they get older. Examining the variations in a person’s microbial makeup can allow us to predict whether the person is lean or obese 90 percent of the time, potentially allowing police to form a picture of a suspect simply from DNA samples.
The human microbiome even affects a woman’s likelihood of contracting human immunodeficiency virus (HIV), and changes the efficacy of anti-HIV drugs. Different species of bacteria inhabit a woman’s vagina, and the dominance of each affects its chemical environment. One species, Lactobacillus, creates an acidic environment inhospitable to many pathogens, effectively reducing the chances of the HIV virus surviving long enough to infect the woman. As one study found, this species is dominant in 90 percent of white women in the U.S., but only in 37 percent of the individuals in a South African province, giving a possible microbiological explanation as to why the rate of HIV infection is overwhelmingly high there in comparison. In contrast, P. bivia is a bacterium that increases the chances of contracting HIV by a factor of 13 when it makes up greater than just 1 percent of the vaginal microbiome.
Tenofovir is one of the most commonly used drugs to both treat HIV and prevent its transmission. It works by inhibiting a protein in the HIV virus called reverse transcriptase, which is an enzyme that allows HIV to multiply and spread. While this drug is effective in men, preventing transmission about 80 percent of the time, it was less than 50 percent effective in women, according to a study in Botswana. While some scientists were tempted to attribute this difference to lower drug efficacy in women, researchers found another cause: Gardnerella. When this bacterium dominates the vagina’s microbiome instead of Lactobacillus, it “gobbles up” the tenofovir, preventing it from reaching the HIV virions and thus failing to inhibit reverse transcriptase.
This new research demonstrates how the vaginal microbiome can help explain the social disparities in HIV infection rates both between genders and between races. The biological differences in our bodies make women living in Africa more likely to contract HIV than white women in the U.S., as well as making preventative drugs less effective in women than in men. It also offers insight into possible solutions to slow the HIV transmission rate, such as killing off harmful bacteria in the vagina like P. bivia and Gardnerella, or introducing helpful bacteria such as Lactobacillus. Either way, further studies of the microorganisms living within us provide a key to living healthier lives, concerning HIV or many other diseases.