The group of people living around you can affect the group of insects living inside you.
The largest and most diverse review to date has found evidence that the environment you live with and the environment you’re raised with can have more of an impact on your microbiome than your lifestyle, age, or even genetics.
If the findings are correct, then the billions of microbes that call our bodies home may be more contagious than we thought. And this can have a huge impact on people’s health.
A study led by biologist Nicola Segata of the University of Trento in Italy fails to show how pathogens jump from one person to another, instead showing the number of intestinal and oral bacteria shared by those around us.
Human interactions, the authors conclude, can help shape the microbiome community and, they say, “may play a role in microbiome-related diseases”.
The findings are based on more than 9,000 saliva samples collected from participants with known connections to each other. These areas were deliberately selected from 20 different countries around the world, not from western or developing countries.
These findings suggest that the billions of symbiotic cells in our bodies can spread between people, even in brief social encounters.
The types of bacteria shared between the participants in the study were found to be ‘abundant’. In fact, researchers found more than 10 million times the bacteria are shared between mothers and babies, in the same household, or in the community.
Previous research has shown that a mother helps to establish her baby’s microbiome in the first few months of life by sharing some of her own microflora, often through vaginal birth, breastfeeding, saliva exchange, or touch.
It is also known that a person’s microbiome can change throughout their life depending on what they eat, how much they exercise, or where they live.
In comparison, human-to-human transmission has not been extensively studied. The results of the latest analysis show that it is an oversight.
As expected, mother-to-child transmission is the most important method of diagnosis. In 711 cases, about 50 percent of the same bacteria were shared between mother and child in the first year of life, and 16 percent of the species came from the mother in particular.
In addition, these pathogens can be detected very late, even at low levels. For example, at age 30, the average person in the study retained about 14 percent of their mother’s original bacteria. Even at the age of 85, the most contagious disease of the mother was still present in her children.
As a person ages, the mother’s microbial capacity is associated with other relationships. Who a person lives and interacts with on a daily basis appears to have a significant impact on the composition of their microbiome.
For example, after four years, researchers found that a child shares the same proportion of bacteria from its mother and father. In addition, fraternal twins who live far apart, have small groups that share their intestines.
All in all, about 12 to 32 percent of the bacteria found in the gut and mouth are shared with others under the same roof. Similar life factors were not sufficient to explain the results.
“As we grow up, the sources of our microbiomes are often the people we interact with,” explains Segata.
“The contact time – think for example students or friends sharing an apartment – is equal to the number of bacteria that have been changed.”
When the authors turned to larger areas, they observed a similar, but smaller, relationship.
Less than 1 percent of the bacteria appeared to jump into rural households, making transmission of the virus extremely rare. That said, the prevalence of bacterial species and rural areas was very similar across data sets.
In about 67 percent of the communities studied, people from the same village but from different families had more pathogens than families from other villages.
These findings suggest that even superficial interactions can affect the human microbiome, for better or worse. While some viruses can bring health benefits, others can weaken the microbe, leaving people susceptible to illness or disease.
“The spread of pathogens has important implications for our health, because some non-communicable diseases (such as heart disease, diabetes or cancer) are associated with changes in the microbiome,” explains Segata.
“Demonstrating that human microbes are transmissible may indicate that some diseases (currently thought to be non-infectious) may be transmissible to some extent.”
This study was published in Nature.