冠状病毒并不新鲜； 它们与世界上的任何东西一样古老，并且已知会导致人类感冒多年。 然而，其最新变种“SARS-CoV-2”目前因引起 Covid-19 大流行是新的。
Often, common cold (caused by 冠状病毒 和别的 病毒 如鼻病毒）与流感混淆。
Flu and common cold, though both present similar symptoms are different in the sense that they are caused by different 病毒 共。
Flu or influenza 病毒 have a segmented genome which cause antigenic shift which occurs due to recombination among 病毒 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 病毒 accumulating mutations (change in its 的DNA 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 病毒. 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 冠状病毒 is normally limited to cold symptoms only and rarely made anyone seriously sick. However, there were some virulent forms of 冠状病毒 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 冠状病毒.
最新的 变种 of 冠状病毒， 小说 冠状病毒 (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 病毒 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 冠状病毒 reportedly underwent changes in its genome that made it into a highly virulent variant, responsible for the current pandemic.
但是，是什么导致了如此剧烈的抗原漂移，使 SARS-CoV-2 具有如此强的毒性和传染性？
科学界有几种理论指向 SARS-CoV-2 的起源3,4. Proponents of man-made origin of the 病毒 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 因为如果人类要创造 病毒 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 病毒.
Be as it may, the fact of the matter remains that a certain almost innocuous 病毒 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 进化?
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参考文献：
- Padron-Regalado E. SARS-CoV-2 疫苗：来自其他冠状病毒株的教训 [提前在线发布，2020 年 23 月 XNUMX 日]。 感染疾病. 2020;9(2):1-20. doi: https://doi.org/10.1007/s40121-020-00300-x
- Liangsheng Z, Fu-ming S, Fei C,zhenguo L. 2019 新型冠状病毒的起源和演变， 临床传染病，第 71 卷，第 15 期，1 年 2020 月 882 日，第 883-XNUMX 页，DOI：https://doi.org/.1093/cid/ciaa112
- Morens DM、Breman JG 等人 2020。COVID-19 的起源及其重要性。 美国热带医学和卫生学会。 在线提供：22 年 2020 月 XNUMX 日。DOI： https://doi.org/10.4269/ajtmh.20-0849
- York A. 新型冠状病毒会从蝙蝠身上飞走？ Nat Rev Microbiol 18, 191 (2020)。 DOI：https://doi.org/10.1038/s41579-020-0336-9
- Andersen KG, Rambaut, A., Lipkin, WI et al. SARS-CoV-2的近端起源。 Nat Med 26, 450–452 (2020)。 DOI： https://doi.org/10.1038/s41591-020-0820-9.
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