کورونا وائرس نئے نہیں ہیں۔ یہ دنیا کی کسی بھی چیز کی طرح پرانے ہیں اور عمروں سے انسانوں میں عام سردی کا سبب بنتے ہیں۔ تاہم، اس کا تازہ ترین ورژن، 'SARS-CoV-2' فی الحال وجہ کے لیے خبروں میں ہے۔ کوویڈ ۔19 وبائی بیماری نئی ہے۔
Often, common cold (caused by کورونوایرس اور دیگر وائرس جیسے rhinoviruses) فلو کے ساتھ الجھ جاتا ہے۔
Flu and common cold, though both present similar symptoms are different in the sense that they are caused by different وائرس ایک ساتھ.
Flu or influenza وائرس have a segmented genome which cause antigenic shift which occurs due to recombination among وائرس 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 وائرس accumulating mutations (change in its 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 وائرس. 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 کورونا وائرسز is normally limited to cold symptoms only and rarely made anyone seriously sick. However, there were some virulent forms of کورونا وائرسز 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 کورونوایرس.
تازہ ترین مختلف of کورونوایرس, the novel کورونوایرس (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 وائرس 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 کورونوایرس reportedly underwent changes in its genome that made it into a highly virulent variant, responsible for the current pandemic.
لیکن اس طرح کے سخت اینٹی جینک بڑھے کی وجہ کیا ہوسکتی ہے جس نے SARS-CoV-2 کو اتنا زہریلا اور متعدی بنا دیا؟
سائنسی برادری میں SARS-CoV-2 کی اصل کی طرف اشارہ کرنے والے کئی نظریات موجود ہیں3,4. Proponents of man-made origin of the وائرس 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 کیونکہ اگر انسان تخلیق کرتے وائرس 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 وائرس.
Be as it may, the fact of the matter remains that a certain almost innocuous وائرس 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 ارتقاء?
***
حوالہ جات:
- Padron-Regalado E. SARS-CoV-2 کے لیے ویکسینز: دیگر کورونا وائرس کے اسباق [پرنٹ سے پہلے آن لائن شائع، 2020 اپریل 23]۔ انفیکشن. 2020;9(2):1-20. doi: https://doi.org/10.1007/s40121-020-00300-x
- Liangsheng Z, Fu-ming S, Fei C, Zhenguo L. Origin and Evolution of the 2019 Novel Coronavirus, کلینکل متعدی امراض، جلد 71، شمارہ 15، 1 اگست 2020، صفحات 882–883، DOI:https://doi.org/.1093/cid/ciaa112
- مورینس DM, Breman JG, et al 2020. The Origin of COVID-19 اور یہ کیوں اہمیت رکھتا ہے۔ امریکن سوسائٹی آف ٹراپیکل میڈیسن اینڈ ہائجین۔ آن لائن دستیاب: 22 جولائی 2020۔ DOI: https://doi.org/10.4269/ajtmh.20-0849
- یارک اے ناول کورونا وائرس چمگادڑوں سے پرواز کرتا ہے؟ Nat Rev Microbiol 18, 191 (2020)۔ DOI:https://doi.org/10.1038/s41579-020-0336-9
- اینڈرسن KG, Rambaut, A., Lipkin, WI ET اللہ تعالی. SARS-CoV-2 کی قربت کی اصل۔ نٹ میڈ 26، 450–452 (2020)۔ DOI: https://doi.org/10.1038/s41591-020-0820-9.
***
