The human body is inhabited by a dizzying number of microorganisms - several hundred trillion. This is about the same as his own cells. However, despite the development of microbiology and the emergence of new visualization methods, researchers today are not aware of all the microbes that consider humans to be their "home".
To be precise, less than 1% of microorganisms have so far been studied that coexist - peacefully or hostilely - with humans. This conclusion was made by specialists from Stanford University, studying fragments of human DNA.
The discovery, as is often the case, was made by accident. Initially, scientists were looking for non-invasive methods to help determine whether a person's body would reject the transplanted organ or take it for its own. This usually requires a biopsy, but experts believe it can be replaced with a simple blood test. In a sample, it is enough to analyze cell-free DNA, as well as DNA fragments, DNA freely circulating in the blood plasma. In addition to the patient's DNA, these samples must 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 such studies, scientists collected blood samples from 156 patients who were about to have a heart, lung or bone marrow transplant. Among them, there were 32 pregnant women, the authors note (this is important, since pregnancy changes the immune system). The results of these studies suggested detectable changes in the microbiota of people with impaired immune systems.
However, experts noticed one oddity: 99% of all fragments of inhuman DNA, they simply could not match with any sample from the genetic databases.
When they started to categorize the unidentified DNA, it turned out that the vast majority of the fragments belonged 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 was made up of TTV viruses (transfused), which are often found in immunocompromised patients.
“We've doubled the number of known viruses in this family thanks to this work,” says lead author Stephen Quake. More importantly, his colleagues discovered a completely new group of TTV viruses.
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Let us explain that pathogens of this type are divided into several groups: some infect humans, the other in animals. However, many of the viruses found by the researchers, although they belonged to the TTV class, did not fit into any of these groups.
“We have found a whole new type of virus infecting humans that is closer in characteristics to viruses that infect animals,” Quake explained.
In his opinion, the discovery of a huge number of unknown viruses can hardly be called surprising. The fact is 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 turned to it, and billions of the rest remain unnoticed, the scientist argues.
His team will continue to study the human microbiota and classify various types of unidentified microorganisms. Among the most important goals is the search for pathogens that are potentially capable of provoking global pandemics. Studying such viruses will help doctors control the situation and be prepared for even the slightest outbreaks of infection.
In addition, scientists plan to study the microbiota of animals using the same principle to identify dangerous viruses that can be transmitted to humans. It is likely that if such work had been carried out earlier, outbreaks of bird and swine flu would have been avoided.
The scientific work of American researchers is published in the Proceedings of the National Academy of Sciences.
Earlier, we recall, scientists explained why viruses and bacteria pity women and do not appreciate men at all. In addition, it is bacteria and viruses that help a person choose a mate for life.