Koronavirusi nisu novi; oni su stari koliko i bilo što na svijetu i poznato je da godinama izazivaju prehladu među ljudima. Međutim, njegova najnovija varijanta, 'SARS-CoV-2' trenutno u vijestima za izazivanje Covid-19 pandemija je nova.
Often, common cold (caused by koronavirusa i druge virusi kao što su rinovirusi) brka se s gripom.
Gripa i obična prehlada, iako oba imaju slične simptome, različiti su u smislu da ih uzrokuju različiti virusi.
Flu or influenza viruses have a segmented genome which cause antigenic shift which occurs due to recombination among viruses 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 virus accumulating mutations (change in its DNA struktura) tijekom vremenskog razdoblja koje uzrokuje promjene u prirodi površinskih proteina. Sve to otežava razvoj cjepiva protiv njih koje bi moglo pružiti dugotrajnu zaštitu. Posljednja pandemija španjolske gripe iz 1918. koja je ubila milijune ljudi bila je uzrokovana gripom ili virusom gripe. Ovo se razlikuje od koronavirusa.
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 koronaviruse is normally limited to cold symptoms only and rarely made anyone seriously sick. However, there were some virulent forms of koronaviruse 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 koronavirusa.
Najnoviji varijanta of koronavirusa, roman koronavirusa (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 virus 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 koronavirusa reportedly underwent changes in its genome that made it into a highly virulent variant, responsible for the current pandemic.
No, što je moglo uzrokovati tako drastičan pomak antigena što je SARS-CoV-2 učinio tako virulentnim i zaraznim?
U znanstvenoj zajednici postoji nekoliko teorija koje upućuju na podrijetlo SARS-CoV-23,4. Proponents of man-made origin of the virus 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 jer ako bi ljudi stvarali virus 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 virus.
Be as it may, the fact of the matter remains that a certain almost innocuous virus 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 evolucija?
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Reference:
- Padron-Regalado E. Cjepiva za SARS-CoV-2: pouke iz drugih sojeva koronavirusa [objavljeno online prije tiska, 2020. travnja 23.]. Infektivna 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. Podrijetlo i evolucija novog koronavirusa iz 2019., Klinička Infectious Diseases, Svezak 71, Broj 15, 1. kolovoza 2020., stranice 882–883, DOI:https://doi.org/.1093/cid/ciaa112
- Morens DM, Breman JG, et al 2020. Porijeklo COVID-19 i zašto je to važno. Američko društvo za tropsku medicinu i higijenu. Dostupno na internetu: 22. srpnja 2020. DOI: https://doi.org/10.4269/ajtmh.20-0849
- York A. Novi koronavirus bježi od šišmiša? Nat Rev Microbiol 18, 191 (2020). DOI:https://doi.org/10.1038/s41579-020-0336-9
- Andersen KG, Rambaut, A., Lipkin, WI sur. Proksimalno porijeklo SARS-CoV-2. Nat Med 26, 450–452 (2020). DOI: https://doi.org/10.1038/s41591-020-0820-9.
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