Where do Corona virus variants come from?

Evolutionary mapping in chronic corona patients Reveals the way to the formation of a variant * In immunocompromised patients, chronic coronary heart disease sometimes develops. The study found that the damaged immune system of these patients was unable to eliminate the virus, which in turn develops over time mutations that confer resistance to antibodies and are more contagious.

Prof. Adi Stern. Photo: Tel Aviv University spokeswoman

A new study by Tel Aviv University estimates that the many variants of corona are formed in chronic corona patients who suffer from severe damage to the immune system. The researchers estimate that these chronic patients suffer from little activity of the immune system in the lung area, and the variants take advantage of this to evade the weak immune system and stay in the body for a long time. However, according to the researchers, it is likely that the ability of the virus to survive and reproduce in the patient’s body indefinitely leads to the fact that there is not necessarily an advantage in developing mutations that encourage human-to-human transmission, and therefore the formation of a rapidly spreading variant is rare. But, when the number of infections around the world reaches a particularly high number, that rare event becomes a reality.

The study was led by Prof. Adi Stern and doctoral student Shari Harari from the Shmonis School of Biomedical Research and Cancer Research, Faculty of Life Sciences, Tel Aviv University. The study was published in the prestigious journal Nature Medicine.

Prof. Stern explains that since the outbreak of the corona, the rate of mutations in the virus has created many questions. On the one hand, in the first year of the epidemic a relatively slow rate of mutation accumulation was observed. On the other hand, since the end of 2020, variants that are characterized by a large number of mutations, far beyond what is expected, occasionally “jump” into our lives. Various hypotheses in the world of science about the link between chronic coronary heart disease and the rate of mutation formation have surfaced, but the issue has not yet been proven. In the new study, Prof. Stern and her laboratory staff illuminate some of the complex puzzle and try to answer the scientific question of how variants are formed.

Prof. Stern explains: “The corona is characterized by the fact that in every population there are people who become infected with chronic corona. In these patients, the virus stays in their body for a long time and they are at high risk for recurrent disease. In all cases observed so far, Weakened, when one of the arms of the system is damaged and does not function. In evolutionary terms, these patients constitute an ‘incubator’ of viruses and mutations – the virus stays in their body for a long time and manages to adapt to the immune system and treatments the patient receives by accumulating various mutations.

The study included an examination of chronic corona patients at the Ichilov Hospital, Tel Aviv Sourasky Medical Center. According to Prof. Stern, the results point to a complex picture: on the one hand, there is no direct connection between drug treatment and the development of variants. On the other hand, it has been found that it is the patients’ defective immune system that creates pressure on the virus to change. In fact, the researchers found that there were chronic patients who showed a pattern of apparent recovery, and then the disease recurred. In all those patients, the virus returned mutantly, meaning that recovery was not complete, which is partly reminiscent of the mode of action of the HIV virus after poor drug treatment.

On closer examination of some patients, the researchers found that when there is a pattern of apparent recovery (based on negative swab tests sampled from the pharyngeal and nasal regions), the virus actually continues to exist in health. The researchers therefore suggested that the virus accumulates healthy mutations, then “climbs” back to the upper respiratory tract.

However, such a picture is complex: the researchers found that although chronic patients are characterized by different combinations of mutations that allow for antibody evasion, this is not the whole picture. Precisely known mutations that allow the virus to be transmitted from person to person effectively – the same mutations have never been observed in the virus that infects chronic patients. This is a gratifying finding – it indicates that not every variant that is created in the bodies of chronic patients, will become a variant with the ability to spread in the general population.

Prof. Stern: “In deep thought, these effects can be explained as follows: The variant was able to settle in a chronic patient suffering from a damaged immune system, he actually found a ‘comfortable’ body where he can stay and exist for a long time. Under these conditions the virus improves positions within the patient’s body. “And it’s unmotivated ‘to pass on to another person. Mutations that allow other people to pass can also be’ at the expense ‘of antibody evasion, so the virus will give up such mutations in favor of evading mutations from the patient’s immune system.”

Prof. Stern concludes: “The corona reveals its complexity and poses many challenges to the scientific community. I believe our research has succeeded in uncovering a missing tier in the big picture, and allowing an opening for further research to discover the origins of the various variants. At great risk from corona disease itself, and which may constitute a reservoir for the formation of the next variant. “

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