Koronavirusi niso novi; ti so stari kot karkoli na svetu in znano je, da že stoletja povzročajo prehlad pri ljudeh. Vendar pa je njegova najnovejša različica, 'SARS-CoV-2', trenutno v novicah za povzročanje Covid-19 pandemija je nova.
Often, common cold (caused by koronavirus in drugih virusi kot so rinovirusi) zamenjujejo z gripo.
Gripa in prehlad, čeprav imata podobna simptoma, sta različna v smislu, da ju povzročajo popolnoma različni 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) v določenem časovnem obdobju, ki povzroči spremembe v naravi površinskih beljakovin. Vse to otežuje razvoj cepiva proti njim, ki bi lahko zagotovilo dolgotrajno zaščito. Zadnjo pandemijo španske gripe iz leta 1918, ki je ubila milijone ljudi, je povzročila gripa ali virus gripe. To 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 koronavirusi is normally limited to cold symptoms only and rarely made anyone seriously sick. However, there were some virulent forms of koronavirusi 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 koronavirus.
Najnovejša varianta of koronavirus, the novel koronavirus (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 koronavirus reportedly underwent changes in its genome that made it into a highly virulent variant, responsible for the current pandemic.
Toda kaj je lahko povzročilo tako drastičen antigenski premik, zaradi česar je SARS-CoV-2 tako virulenten in nalezljiv?
V znanstveni skupnosti obstaja več teorij, ki kažejo na izvor 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 ker če bi ljudje ustvarili 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. Cepiva za SARS-CoV-2: Lekcije drugih sevov koronavirusa [objavljeno na spletu pred tiskanjem, 2020. april 23]. Okuži 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. Izvor in razvoj novega koronavirusa 2019, Klinični Nalezljive bolezni, letnik 71, številka 15, 1. avgust 2020, strani 882–883, DOI:https://doi.org/.1093/cid/ciaa112
- Morens DM, Breman JG, et al 2020. Izvor COVID-19 in zakaj je to pomembno. Ameriško združenje za tropsko medicino in higieno. Dostopno na spletu: 22. julija 2020. DOI: https://doi.org/10.4269/ajtmh.20-0849
- York A. Novi koronavirus zbeži pred netopirji? Nat Rev Microbiol 18, 191 (2020). DOI:https://doi.org/10.1038/s41579-020-0336-9
- Andersen KG, Rambaut, A., Lipkin, WI et al. Proksimalni izvor SARS-CoV-2. Nat Med 26, 450–452 (2020). DOI: https://doi.org/10.1038/s41591-020-0820-9.
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