We share up to one-third of the bacteria in our mouth with the people closest to us.
Some diseases considered non-communicable, such as cancer, could have a contagious component due to microorganisms in the digestive tract.
The new study analyzed stool and saliva samples from some 5,000 people from 20 countries on five continents.
The results show that social interactions determine the composition of the so-called microbiome, even in the gut. A mother shares 34% of the bacterial strains in her heart with her young children. Two people are living together, 12%. Two twin siblings are living in different households, 8%. And two independent adults from the same town, also 8%. Inherited microorganisms are lost after birth: living together determines the microbiome. "The percentage that an adult shares with his or her mother are the same as the percentage that he or she shares with people he or she lives with or co-workers," says Vallès of the University of Trento, Italy.
Three out of four deaths worldwide are caused by non-communicable diseases like cancer, heart attacks, stroke, diabetes, and asthma. More than 40 million people die each year worldwide from these causes, according to the World Health Organization. Canadian microbiologist Brett Finlay launched a provocative hypothesis three years ago. "Are noncommunicable diseases communicable?" he asked in the journal Science. Finlay argued that factors such as junk food, smoking, and alcohol consumption lead to an imbalance in the microbiome, which can influence noncommunicable diseases or risk factors, such as obesity. This altered microbiome "could be transmitted from person to person, potentially contributing to the spread of disease," according to Finlay.
The new work points in that same direction. "Our results reinforce the hypothesis that several diseases and conditions currently considered non-communicable should be re-evaluated," the authors state in their study, published Wednesday in the journal Nature, the cutting edge of the world's best Science. It is the most extensive investigation into the transmission of the human microbiome conducted to date.
The signatories have looked at more than 800 species of bacteria, identifying the ultra-specific strains of each person. "Sharing 8% is a lot because with whom we have not been in contact, we have zero," stresses Vallès, born 32 years ago in Vic (Barcelona). Her study confirms that the mouth's microbiome is transmitted differently from the depths of the digestive tract. "Orally, the vehicle is saliva, but we still don't know the specific mechanism in the intestinal tract. It could be through lack of hygiene, through a fecal-oral transmission that reaches the intestine, but it is unclear, " the microbiologist acknowledges.
These results reinforce the concept that you can acquire potentially harmful disease-causing microbes from other people in a transmissible way.
