Коронавирусите не са нови; те са толкова стари, колкото всичко на света и е известно, че причиняват обикновена настинка сред хората от векове. Въпреки това, последният му вариант, "SARS-CoV-2", в момента е в новини за причиняване Covid-19 пандемията е нова.
Often, common cold (caused by коронавирус и други вируси като риновируси) се бърка с грип.
Flu and common cold, though both present similar symptoms are different in the sense that they are caused by different вируси напълно.
Flu or influenza вируси have a segmented genome which cause antigenic shift which occurs due to recombination among вируси of the same genus, thus changing the nature of the proteins on the viral surface responsible for generating immune response. This is further complicated by a phenomenon called antigenic drift which results from вирус accumulating mutations (change in its ДНК structure) over a period of time that causes changes in the nature of surface proteins. All this makes it difficult to develop vaccine against them that could provide protection for long duration. The last pandemic of Spanish Flu of 1918 that killed millions of people was caused by flu or influenza вирус. This is different from the coronaviruses.
Coronaviruses, responsible for causing Common cold, on the other hand, do not possess a segmented genome hence there is no antigenic shift. They were minimally virulent and occasionally lead to death of the affected people. The virulence of короновирусите is normally limited to cold symptoms only and rarely made anyone seriously sick. However, there were some virulent forms of короновирусите in the recent past, namely SARS (Severe Acute Respiratory Syndrome) that appeared in 2002-03 in Southern China and caused 8096 cases, resulting in 774 deaths in 26 countries and MERS (Middle East Respiratory Syndrome) that appeared 9 years later in 2012 in Saudi Arabia and caused 2494 cases, resulting in 858 deaths in 27 countries1. However, this remained endemic and disappeared relatively quickly (within 4-6 months), possibly due to its less virulent nature and/or by following proper epidemiological procedures for containment. Hence, no need was felt at that time to invest heavily and develop a vaccine against such a коронавирус.
Последният вариант of коронавирус, the novel коронавирус (SARS-CoV-2) seems to be related to SARS and MERS2 which is highly infectious and virulent in humans. It was identified first in Wuhan China but soon became an epidemic and spread across the world to take the form of pandemic. Was this rapid spread across select geographies solely due to the high virulence and infectivity caused by changes in the genetic constitution of the вирус or possibly due to lack of timely epidemiological intervention by reporting to the concerned national/transnational authorities which prevented timely containment measures, thereby causing about a million deaths so far and bringing the world economy to the grinding halt.
This is the first time in the human history that the existing коронавирус reportedly underwent changes in its genome that made it into a highly virulent variant, responsible for the current pandemic.
Но какво може да е причинило такъв драстичен антигенен дрейф, което прави SARS-CoV-2 толкова вирулентен и заразен?
В научната общност има няколко теории, които сочат произхода на SARS-CoV-23,4. Proponents of man-made origin of the вирус believe that the genome changes seen in SARS-CoV-2 would take am extremely long period of time to develop naturally, while other studies argue that it may be of natural origin5 защото ако хората трябваше да създадат вирус artificially, why would they create a sub-optimal form that is virulent enough to cause a severe disease but binds sub-optimally to the human cells and the fact that it was not created using the backbone of the known вирус.
Be as it may, the fact of the matter remains that a certain almost innocuous вирус underwent genetic changes to transform itself to become mildly virulent SARS/MERS, and finally into a highly infectious and virulent form (SARS-CoV-2) in a span of 18-20 years, appears unusual. Such drastic antigenic drift, which incidentally has a continuum in between, would be highly unlikely to happen in a normal course, in the laboratory of Mother Earth, in such a short time duration. Even if it were to be true, what’s more perplexing is the environmental pressure that would have triggered such a selection in the еволюция?
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Литература:
- Padron-Regalado E. Ваксини за SARS-CoV-2: уроци от други щамове на коронавирус [публикувано онлайн преди печат, 2020 април 23 г.]. Инфектирайте Dis Ther. 2020;9(2):1-20. doi: https://doi.org/10.1007/s40121-020-00300-x
- Liangsheng Z, Fu-ming S, Fei C, Zhenguo L. Произход и еволюция на новия коронавирус от 2019 г., Клинични инфекциозни болести, том 71, брой 15, 1 август 2020 г., страници 882–883, DOI:https://doi.org/.1093/cid/ciaa112
- Morens DM, Breman JG и др. 2020 г. Произходът на COVID-19 и защо има значение. Американското дружество по тропическа медицина и хигиена. Наличен онлайн: 22 юли 2020 г. DOI: https://doi.org/10.4269/ajtmh.20-0849
- Йорк А. Новият коронавирус бяга от прилепите? Nat Rev Microbiol 18, 191 (2020). DOI:https://doi.org/10.1038/s41579-020-0336-9
- Andersen KG, Rambaut, A., Lipkin, WI и др. Близкият произход на SARS-CoV-2. Nat Med 26, 450–452 (2020). DOI: https://doi.org/10.1038/s41591-020-0820-9.
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