Immigrants in the US are helping scientists understand how gut bacteria can be contagious

Sharing more than just a city.
Sharing more than just a city.
Image: Reuters/Lucas Jackson
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Pajau “PJ” Vangay has gotten really good at talking about poop in front of strangers.

Vangay is a graduate student in computational biology at the University of Minnesota who’s gathering data about the human microbiome: the bacteria that live all over our bodies, but mostly within our digestive tract. In a single human body, these organisms can outnumber human cells 10 to one by some estimates, and some scientists say they carry out enough biological processes—playing roles in our immune and digestive systems—to be considered a sort of human organ (paywall). Because most of them live in our colons, the best way to study them is through stool samples.

Vangay collected her samples from immigrants—specifically, Hmong and Karen immigrants in St. Paul and Minneapolis, Minnesota. The gut bacteria of immigrants, Vangay and others suspect, could have a lot to teach us about how the microbiome impacts human health. Though scientists have been studying gut bacteria for years—most notably with the Human Microbiome Project, launched in 2008 by the US National Institutes of Health—we hardly know anything about immigrant and refugee communities’ gut bacteria.

We should, though, because these particular communities offer an almost perfect case study for a developing theory of gut bacteria: that you can “catch” a bad microbiome.

Trade your bacteria for mine?

We have a give-and-take relationship with our gut bacteria: we house and feed them, while they block out the bad microbes and make vitamins for us (paywall), for example. And when our microbiome get out of whack, things can go wrong for us. Certain populations of gut bacteria, says Dan Knights, a computational biologist at the University of Minnesota and Vangay’s advisor, are strongly correlated with non-communicable diseases like diabetes, heart disease, and cancer.

Our gut microbes are shaped by how we live—for good and bad. First, they’re directly affected by what we put into our bodies. Those who eat diets high in fiber and natural sources of probiotics (like vegetables and yogurts) tend to have more species of gut bacteria; people who eat lots meat and processed foods have less diverse gut species. Less diversity has been linked to obesity (which can come with complications like high blood pressure and diabetes) and autoimmune conditions, like asthma and allergies.

But who we’re surrounded by can also affect the colony of microbes living within us. “Even though you don’t think of gut bacteria being all over you, they kind of are,” Andrew Moller, an evolutionary biologist at the University of California, Berkeley, told Quartz last year. It’s likely that you trade gut bacteria with your fellow humans when you brush up against them on your morning commute.

People who live in different parts of the world have different guts: A 2012 study (paywall) co-authored by Knights examined the gut microbiomes of healthy people living in the Venezuelan Amazon and in US cities, and found vast differences—enough to be able to distinguish different populations based on their gut bacteria alone.

Unique microbiomes can be formed within much smaller communities, as well. In 2014, researchers from the Argonne National Laboratory in Lemont, Illinois looked at (paywall) the microbiomes of seven families over six weeks. They found they could discern whether people lived together based on the similarity of their microbiomes.

And, when you move, your microbiome can change, warping to match the microbiomes of the new humans you find yourself surrounded by. If the local microbiome is unhealthy, that doesn’t bode well for you.

Which is why Vangay wants to study how exactly gut microbiomes in Hmong and Karen immigrants in St. Paul and Minneapolis changed when they moved to the US. Though most members of these communities have access to better health care in Minnesota than they did back home, rates of certain illnesses do go up among the Hmong and Karen once they’ve lived in the US for a while: non-communicable diseases like diabetes, heart disease, and cancer. They also are more likely to be overweight and obese.

Vangay thinks something about their health changed when they move to the US. Rather than an obvious diet or lifestyle change, she suspects it’s the collection of microbes in their guts. If she can find a link between their microbiomes, their time spent in the US, and obesity rates, perhaps she can figure out how some kind of intervention could prevent weight gain from happening before it starts.

The microbes Hmong us

Even though the science of microbiome analysis is relatively simple—just sequencing the genetic material found within stool samples—gathering the data has taken her a while. First she spent a year planning the project, talking to some 20 different local organizations to get their input. Then she—along with some recruits from the community—ventured out to places like churches, markets, and adult education centers to try to explain the work to potential subjects and ask for volunteers.

“It was really hard, initially,” Vangay says. “The fact that we have microbes living in us is fairly new to most people.” Vangay needed to translate these fairly complicated scientific concepts into relatable Hmong and Karen terms. And then, of course, she was asking for stool samples, which breaks social norms in any setting.

“These people have been through a lot. They’re refugees of war, and in general people have a lot of mistrust [of strangers], which is understandable,” says Vangay, who is Hmong herself. It took about a year, but eventually they were able to get the 550 or so female volunteers they needed. (They stuck with women aged 18 to 65 to control for variation between sexes and the elderly.)

The plan now is to see if they can find a relationship between gut microbe makeup, a migrants’ length of time in the US, and weight gain. They’re also comparing the samples to those Vangay took from Hmong living in Thailand and Karen refugees living in camps in Asia. The theory is that the longer immigrants have lived in the US, the more their microbes will have changed, and the more likely they are to be overweight.

Vangay and her team stopped collecting samples in October 2016, and now the next step, likely to be conducted in the spring of this year, is to implant some of the (presumably unhealthy) microbiomes of overweight immigrants into mice through a fecal transplant, and see if changes in diet can prevent the mice from becoming obese.

Then, they would adapt the most successful mouse diets for the Hmong and Karen communities, by figuring out which ingredients used in their traditional cooking styles would also provide the gut-health benefits. That’s key, because that’s the only way an intervention like this would work in practice: For example, southeast Asian groups would be more likely to actually eat mustard greens, winter squash, papaya, and bamboo shoots, which they’ve been eating for years, than kale or granny smith apples, which they may have never even consumed before getting to Minnesota.

That, of course, sounds like a pretty simple solution. But it could make a huge difference by going beyond the basic admonition to “eat healthier” that immigrant communities get now. And down the road, scientists could potentially come up with an intervention that’s more than just a diet. For instance, it’s not too hard to imagine a pill containing a mix of good bacteria that could inoculate against the “bad” microbiome of a place you’re moving to. Or maybe it’d work more like a treatment, restoring your healthy microbiome once you’ve moved. These pills—whether they contain the same bacteria found in a living individual or a carefully crafted synthetic mix—could be the easiest way of preventing or treating conditions related to a microbial imbalance.

Although the field of probiotics is in its infancy (current research about the benefits of these over-the-counter pills is inconclusive), fecal transplants have been put into a pill. These transplants take a donor’s stool, and after some careful sifting, use it to re-colonize the intestine of the recipient. (The pill form significantly makes the concept easier to swallow.) So far, these transplants have been made for those who are deathly ill with infections called Clostridium difficile—but what if they could be made for other conditions, including obesity or, conversely, malnutrition?

Research in these areas is still ongoing, but ideally, scientists would be able to figure out how to harness gut bacteria from any kind of healthy individual and give them to anyone in need—including migrants. That will matter more and more as we continue to become a more global civilization.  We aren’t the only ones who cross borders, after all—our gut bacteria do, too.