Standard definitions says that noncommunicable diseases are thought to stem from a combination of environmental, genetic, and lifestyle factors rather than being transmitted by a virus, fungi, or bacteria. However, in recent years the collections of microbes living in and on the human body have been shown to have a huge influence on health and well being. Could this then mean that noncommunicable diseases may be able to pass between people via the microbiome?
Some scientists are suggesting just that; a study published in the journal Science suggests healthy individuals can potentially catch aspects of ailments through exposure to mixed up microbes. Communities of microbes reside in and on the human body, research suggest these help direct functions of various physiological systems such as digestion, immune defense, and metabolism. While it is not yet known how to distinguish healthy from unhealthy microbiome certain diseases appear to be linked to a bacterial imbalance within the body.
“It is a radical thought to think that noncommunicable diseases might actually be communicable, and this hypothesis gives us a whole new way of thinking about these diseases,” author B. Brett Finlay, a microbiologist at The University of British Columbia in Vancouver, told LiveScience in an email. Several recent studies led Finlay and his colleagues to formulate this hypothesis, but a 2019 study conducted in Fiji really “tipped the scales,” he said.
Saliva and stool samples from 290 people were collected to determine which types of bacteria appeared in their guts. Results revealed distinct patterns of bacterial transmission within each community, in particular among those in the same households; mothers and children shared many microbes but spouses appeared to share the most similarities. According to a study published in the journal Nature Microbiology the researchers were able to predict which participants were a paired couple based on their microbiomes alone.
According to the Fiji study at least some elements of the microbiome can be passed between individuals, this may possibly mean that the transmitted bugs may drive disease: For example spouses of those with type 2 diabetes have a higher chance of developing the disease themselves within a year of their partner’s diagnosis, and similar tends have been revealed in IBD in both human and animal studies. Cardiovascular disease may be linked to the presence of bacteria in the gut, those with high concentrations of TMAO in their blood have an increased risk of developing the disease and their risk will increase if these enzyme producing bacteria appear in the gut. Studies have also shown the bacteria can induce CVD if transferred from a human to a mouse, but it is not known whether the same will occur between humans.
Other studies provide hints that more noncommunicable diseases may be influenced by bacteria and that they may travel between humans. “Our lab has shown that early-life microbes impact hugely on asthma … and we have some very exciting preliminary data with Parkinson’s,” Finlay said. Microbes also alter immune function, which may prove relevant to cancer patients whose immune systems fail to recognize and attack tumors in the body, he added.
Even obesity may involve a potentially transmittable microbe; lean mice become obese after receiving a fecal transplant from an obese mouse, humans with obese friends/siblings have a higher chance of being obese, and living in a country with a high obesity rate increases the risk of being obese.
“Ideally, one does a fecal transfer from a diseased person into a healthy one and causes disease, but of course this can’t be done [for ethical reasons],” he said. Testing the hypothesis will have to rely on animal models and population studies, and if any noncommunicable diseases can be transmitted through microbes, they will meet three criteria: 1) They will appear distinct in diseased people versus healthy people; 2) they will be able to be isolated from a disease host; and 3) they will induce disease when transferred into healthy animals.
“As we identify mechanisms further, we can actually test these mechanisms, inhibit them … and really show microbes are involved,” Finlay said. “Repopulating’ people with lab-grown mixtures of microbes is probably better [than using fecal transplants], as we know exactly what is going in and don’t have to worry about some virus that we haven’t discovered yet being transplanted,” Finlay said. Fecal transfers will be licensed only for fixing “serious diseases,” as the procedure would have to be repeated numerous times, he added.
While there is still much research to do if this hypothesis gets support it may eventually lead to a new understanding of noncommunicable disease. “It has significant public health policy implications,” Finlay said, “and further suggests that looking after your own microbes will not only benefit you but also people close to you.”
