In 2018, a study carried out by Tübingen researchers caused a sensation when they discovered that, contrary to general belief, Alzheimer’s disease might be transmissible. However, an international team of researchers is now adding to the controversy surrounding the potential transmission of “non-communicable diseases.”

Until now, scientists have assumed that conditions such as cardiovascular diseases, cancer or specific lung diseases (which currently account for up to 70 % of non-natural deaths worldwide) are among these “non-communicable diseases.” The World Health Organization (WHO) believes that they are caused by a combination of genetic predispositions along with lifestyle and environmental factors. The possibility of transmission from person to person had previously been ruled out.

However, a team from the “Humans & the Microbiome” program at the Canadian Institute for Advanced Research (CIFAR), together with the participation of Professor Thomas Bosch from the Christian-Albrechts-Universität zu Kiel (CAU, Germany), has now found convincing evidence that many conditions classified as non-communicable diseases could potentially be passed on from person to person via microbiome. The scientists wrote in the Science journal that intestinal flora is involved in the transmission process as well. “If our hypothesis turns out to be correct, it will completely redefine our view of public health,” says Brett Finlay, Professor of Microbiology at the University of British Columbia and head of the CIFAR research programme “Humans & the Microbiome.”

Graphics: V. Altounian/Science

The scientists were able to prove that those with various conditions such as obesity, certain bowel diseases, cardiovascular disease or even type 2 diabetes, human microbiome exhibited substantial differences compared to those with healthy bodies. In addition, they found a wealth of evidence in laboratory experiments that these modified microbiomes led to diseases in previously healthy models of organisms. For example, a mouse of normal weight became overweight after the intestinal microbiome of an obese mouse was transferred to it. “Summing up these facts suggests that many diseases that are not traditionally considered to be communicable could well be transferable,” Finlay says.

Transmission of microorganisms also possible between human beings

Researchers from the Bosch group at the University of Kiel support this hypothesis. “If laboratory animals such as freshwater polyps are not kept separately, but instead for a certain amount of time in a collective living environment, the microbiome first adapts to each other, and then its physical appearance and how it manifests align with each other,” Bosch explains. His team was able to show that the microbes pass from one individual directly to another. “It is possible that this microorganism transfer also takes place when people are co-habiting. For instance, through close social contacts or in shared apartments,” Bosch conjectures.

The authors concede that their hypothesis is somewhat bold and that many of the mechanisms involved are as yet unknown. For one thing, it’s still hasn’t been established in which cases this type of transmission intensifies. Or whether “a healthy state can also be transferred,” says co-author Maria Gloria Dominguez-Bello, professor at Rutgers University in New Jersey. Further research is needed in order to find this out. However, the researchers stress that there is undoubtedly a significant link between a disrupted microbiome and many diseases.

Further research into transmissibility

In future research scientists hope to find out how the microbiome interacts with specific environmental conditions and genetic factors involved in the transfer of diseases, for one thing. “The new hypothesis makes it clear that we need to consider disruptions in the microbial colonization of the body much more than before as a cause of disease. Also we need to explore potential transmission routes more closely,” says Bosch. ” This aspect will be one of the spearheads of our work at our Metaorganism Collaborative Research Center over the next few years.”