99% of microbes living in the human body are unknown to science

The human body is inhabited by a dizzying number of microorganisms – several hundred trillion. It’s about the same as its own cells. However, despite the development of microbiology and the emergence of new methods of visualization, researchers today are not known for all microbes that consider a person their “home”.

To be more precise, so far less than 1% of microorganisms have been studied, coexisting – peacefully or hostilely – with humans. This conclusion was made by specialists from Stanford University, studying fragments of human DNA.

Opening, as is often the case, was made by accident. Initially, scientists were looking for non-invasive ways to help determine whether a person’s body would be rejected by the organ transplanted or whether it would take it for its own. Typically, this requires a biopsy, but experts believe that you can replace it with a simple blood test. In the sample, it is sufficient to analyze cell-free DNA, as well as DNA fragments, DNA that freely circulate in the blood plasma. In addition to the patient’s DNA, these samples should contain DNA fragments from the organ donor, as well as a comprehensive overview of the bacteria, viruses and other microbes that make up the human microbiota.

In several of these studies, scientists collected blood samples from 156 patients who had a heart, lung or bone marrow transplant. Among them there were 32 pregnant women, the authors note (this is important, as pregnancy changes the immune system). The results of these studies suggested the presence of discernible changes in the microbiota of people with impairments in the functioning of the immune system.

However, experts noticed one oddity: 99% of all fragments of non-human DNA, they simply could not be compared to any sample from the genetic databases.

When the researchers started categorizing unidentified DNA, it turned out that the vast majority of fragments belong to a type called proteobacteria. It includes, among many other species, pathogens, the most famous of which are Escherichia coli and Salmonella.

Among the viruses, the largest group consisted of TTV-viruses (transmitted through blood transfusion), which are often found in patients with weakened immunity.

“We have doubled the number of known viruses in this family thanks to this work,” says lead author Stephen Quake. More importantly, his colleagues discovered an entirely new group of TTV viruses.

Let us explain that pathogens of this type are divided into several groups: some affect people, another part – animals. However, many of the viruses found by researchers even belonged to the TTV class, but did not fit into any of these groups.

“We found a whole new type of virus that infects people who are closer to viruses that damage animals,” Quake explained.

In his opinion, the discovery of a huge number of unknown viruses is hardly surprising. The fact that researchers in the study of microbiota mainly focus on only one specific organ of the human body – skin, intestines and so on. In addition, when a new microorganism is discovered, all attention is drawn to it, and billions of others remain unnoticed, the scientist argues.

His team will continue to study the human microbiota and the classification of various types of unidentified microorganisms. Among the most important goals is the search for pathogens that are potentially capable of provoking global pandemics. The study of such viruses will help doctors to monitor the situation and be ready even in the slightest outbreaks of infection.

In addition, scientists plan on the same principle to investigate the microbiota of animals to identify dangerous viruses that can be transmitted to humans. Probably, if such work was done earlier, outbreaks of avian and swine flu could be avoided.

The scientific work of American researchers is published in the Proceedings of the National Academy of Sciences.

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