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People during the early years were plagued by tuberculosis infections, malaria, constant syphilis outbreaks and wounds that were laced with bacteria and never healed. But armed with vaccines and antibiotics, modern-day humans can now avoid or be treated for these and many other diseases, illnesses caused by infectious agents that can be transmitted between people or from animals to humans. 

Lately, most people do not die from communicable diseases but rather those that can't be passed on to other people. Around 41 million people around the world die every year from cardiovascular disease, respiratory disease, cancer, diabetes or another chronic illness. Noncommunicable diseases account for 70% of deaths around the world, according to the World Health Organization

Noncommunicable diseases are thought to arise from a combination of environmental, genetic and lifestyle factors instead of being transferred by bacteria, viruses or fungi. In recent years, scientists have realized that the collection of microbes crawling in and on the human body has a massive influence on our health. Also known as the microbiome, is it possible that noncommunicable diseases can be passed between people through the microbiome? There are scientists that think that the answer is yes. 

An interesting hypothesis on microbes

Communities of microbes make their abode in the body of humans and research suggests that these bugs help direct the function of numerous physiological systems, including digestion, metabolism and immune defense. Scientists do not yet fully understand what distinguishes a healthy microbiome from an unhealthy one, but certain diseases seem to be connected to a bacterial imbalance in the body. 

For example, people with diabetes, cardiovascular disease, and inflammatory bowel disease tend to host a different collection of bacteria in their guts than those without the disease, according to a report published in Science. The research suggests that healthy people could catch aspects of these ailments through exposure to these microbes that are mixed-up. 

Author of the study, B. Brett Finlay, a microbiologist at The University of British Columbia said that it is a radical thought to think that noncommunicable diseases might be communicable, and this hypothesis gives them a whole new way of thinking about these diseases. Numerous studies led Finlay and his colleagues to formulate this hypothesis, but a study in 2019 conducted in Fiji tipped the scales. The results were published in Nature Microbiology. 

Testing the idea 

More studies hint that numerous noncommunicable diseases may be influenced by bacteria and that those bacteria may travel between people. Finlay said that their lab has shown that early-life microbes impact massively on asthma, and they have very exciting preliminary data with Parkinson's. Microbes also alter immune function, which may be relevant to cancer patients whose immune systems fail to recognize and attack tumors in the body. 

Obesity, which is a major risk factor for noncommunicable disease, also involves transmittable microbes. Lean mice that they experimented on become obese when they got a fecal transplant from a mice that was already obese. People with obese friends or siblings have a higher chance of being obese than those who do not have obese friends or siblings. Living in a place with a high obesity rate can also raise a person's risk of being obese.   

However, all of these studies raise a similar question: How can scientists tell which aspects of the disease are linked to microbes, as opposed to exercise, diet, genes or environmental factors?

Finlay said that this is a difficult question to answer. He said that ideally, one does a fecal transfer from a diseased person into a healthy one and causes disease, but this can't be done for ethical reasons. To test the hypothesis, he and his colleagues will have to rely on animal models and population studies akin to the one conducted in Fiji.

If there are any noncommunicable diseases that can be transmitted through microbes, the bugs will meet three criteria. They will appear distinct in diseases people versus the healthy ones, they will be able to be isolated from a diseased host and they will include disease when transferred into healthy animals. 

Finlay said that as they identify the mechanisms further, they can test the mechanisms, inhibit them and show all the microbes that are involved.

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