A recent paper outlines an intriguing new theory. The authors ask whether the microbes that inhabit the human body could transfer diseases such as diabetes and heart disease from person to person.
Our resident bacteria play a role in certain diseases. Could they also be involved in passing diseases among individuals?
The importance of the microbiome is currently at the forefront of scientific discourse. Experts and the public are equally absorbed by the fascinating influence of microbes on human health.
A new theoretical paper, published in the journal Science, takes the discussion one step further. The authors ask whether conditions such as cardiovascular diseases, cancer, and chronic respiratory illnesses could be transmitted from one individual to another via the bacteria, fungi, and viruses that live on and in us.
The paper, which is titled “Are noncommunicable diseases communicable?” is likely to spark lively debate and a glut of new research. Because scientists now believe that the microbiome plays a role in many diseases, the authors ask whether it could also play a part in transmitting diseases among individual.
Heart disease, cancer, and lung conditions are called “noncommunicable” diseases (NCDs) because they result from genetic, environmental, and lifestyle factors: Therefore, they cannot be passed from person to person.
Over the last 100 years, mortality rates from communicable diseases, caused by infectious microbes, have fallen dramatically. During the same period, mortality rates from NCDs have risen sharply, now accounting for 71% of deaths globally.
Researchers have demonstrated that changes in the microbiome accompany a wide range of diseases, including diabetes, Parkinson’s disease, heart disease, and cancer.
At the same time, scientists have found that the composition of our microbiome appears to mirror those of the people we live among.
For instance, the paper explains that unrelated people who live together have more similar gut bacteria than close relatives who live apart. Scientists currently believe that this similarity results from the shared diet and environment of people who cohabit; but could there be more to it?
The authors of the current paper synthesize these ideas; they explain that “Some NCDs could have a microbial component and, if so, might be communicable via the microbiota.” This would make NCDs communicable.
As it stands, evidence for this brave new theory is circumstantial, but it certainly merits further scrutiny.
The authors refer to a study of 12,067 individuals that spanned 32 years and report that “Having an obese friend was associated with a 57% higher chance of being obese, and there was a 40% higher chance of obesity if a sibling was obese.”
Once again, this association could be due to diet, environment, and genetics. Friends and siblings may be more likely to live in similar locations and eat similar foods. But aside from shared behaviors, the authors of the present paper wonder whether individuals might pass along certain microbes that increase the risk of developing obesity.
Obesity is a risk factor for type 2 diabetes, and if we suppose that obesity is transmissible from our microbiome to another’s, it would imply that diabetes could also be considered a communicable disease.
Of course, this is a theory based on a theory, and there is only circumstantial evidence to back it up. As an example of this evidence, the authors explain that “Within a year of a [type 2 diabetes] diagnosis, spouses have a higher chance of developing [type 2 diabetes], and this trend remains over 3 years after the initial diagnosis.”
Again, this could just as easily be explained by two people sharing an environment and dietary habits.
A compelling idea
More convincingly, the authors refer to results of various studies that have found that transferring feces from one mouse with a certain disease to another mouse without that disease can cause the second animal to develop the illness; they write:
“[Fecal microbiota transplant] of dysbiotic microbiota from individuals with various NCDs into healthy animals results in disease, such as [cardiovascular disease, irritable bowel disorder, type 2 diabetes], and many others.”
In short, the authors explain that disturbances in the microbiome can produce disease and that when scientists transplant these microbial communities into another animal, that animal becomes sick. They continue:
“These observations suggest that the microbiota could be a causal and transmissible element in certain diseases that have been traditionally classified as NCDs.”
This theoretical road may run both ways, too; the authors outline how “transmissible microbiota, especially early in life, may also have a protective role against NCDs.”
To date, bacteria are the most studied components of the microbiome, but it is possible that viruses — which outnumber resident bacteria — could also play a role in making NCDs transmissible.
As the authors write, scientists will need to carry out specific research to prove whether NCDs can, in fact, be communicated. Distinguishing between the effects of environment and any effects of microbial transfer will be challenging indeed.
This recent paper, however, is not meant to convince us that gut bacteria are transferring NCDs throughout the population. The authors simply hope that their “hypothesis stimulates additional discussion and research.” It is sure to do just that.
DiabetesHeart DiseaseGastroIntestinal / GastroenterologyInfectious Diseases / Bacteria / Viruses
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