When researchers first began studying the rates of HIV transmission in Nairobi sex workers, they discovered that many people who were exposed to HIV multiple times never ended up contracting the disease. But why?
It turns out, there are differences in an individual’s immune responses that can protect them against HIV, which can be affected by the microbiome in their reproductive tract.
Dr. Paul McLaren, a research scientist at the Public Health Agency of Canada’s National Microbiology Laboratory (NML), studies why people’s bodies respond differently to HIV exposure and how genetic differences in people can affect the rate of disease progression. Dr. McLaren is collaborating with partners at the University of Manitoba, the Centre for the AIDS Programme of Research in South Africa and the University of Nairobi on a project looking into this link between the microbiome and HIV.
What is the microbiome and how does it affect HIV risk?
The microbiome includes all the microbes (such as bacteria, fungi, and viruses) we live with, either on our bodies or in our bodies. They are found in the reproductive system, digestive tract, urinary tract, on the skin and elsewhere. These microbes are generally not harmful and can be part of a healthy functioning body.
Scientists have discovered that a high diversity of microbes within the vaginal microbiome, a condition called dysbiosis, can make the person more susceptible to HIV. This is in contrast to the microbiome of the digestive tract, where a high diversity of microbes is a good thing. A healthy vaginal microbiome mainly contains the lactobacillus species of bacteria, but a large number of people have a different composition or go through cycles where their composition changes to become more or less diverse.
It is not known why dysbiosis develops in some people and not others, or why it might develop more frequently in some people more than others. Scientists are still studying why dysbiosis can make a person more prone to HIV infection. One theory is that because it causes inflammation in the vaginal tract, it can cause an immune response leading to a breakdown of the tissue barrier lining the tract, causing a flood of immune cells (which are target cells for HIV) and as a result, increasing their risk level.
Genetic influences
Dr. McLaren analyzes microbiome and human data to see if there are any genetic factors that might make it more likely for people to have dysbiotic vaginal microflora and if that relates to their likelihood of contracting HIV.
“Human beings are variable creatures and part of our makeup is influenced by our genetic background. We’ve observed that some people who have a healthy vaginal microbiome have genetic differences that seem to be involved in maintaining a healthy tissue barrier in their vaginal tract,” he says.
The research has produced exciting genetic findings with significant implications in terms of preventing HIV infections.
“If we can understand what causes these dysbioses at the sites of HIV infection, we may be able to intervene and treat people so that they can maintain a healthy microbiome or revert back to a healthy microbiome,” he says.
One more tool in the toolkit
Stigma and discrimination around HIV continue to be barriers to care that prevent some people from accessing resources for prevention, like Pre-exposure prophylaxis (PrEP) for example. Dr. McLaren points to probiotics as a potential treatment for dysbiosis. People take probiotics for a variety of reasons including overall general health. There is no existing stigma related to their use or application, which means that people might be more likely to take them. He notes that probiotics should never replace PrEP, but they are one more tool in their prevention toolkit. Reducing barriers to care, like stigma and discrimination, continues to be a priority for the Government of Canada when it comes to Canada’s HIV response.
“HIV has been around for more than 40 years and we still have around 2000 new infections per year in Canada. While HIV is no longer a death sentence, it means going on antiviral drugs for the rest of your life. Prevention is still very important,” he says.
For Dr. McLaren, while he didn’t originally plan on entering into global health research, it has become a personal issue to him.
“When I travelled to Kenya, I saw how people’s lives were impacted by HIV. The most marginalized populations are the ones most affected. I hope to contribute in some small way to limiting the spread of HIV and I think it’s important to help the people who need our help,” he says.