Koronavirusai nėra naujiena; jie yra tokie pat seni kaip ir bet kas pasaulyje ir yra žinoma, kad per amžius sukelia peršalimą tarp žmonių. Tačiau naujausias jo variantas, „SARS-CoV-2“, šiuo metu yra naujienų dėl sukėlimo Covid-19 pandemija nauja.
Often, common cold (caused by koronavirusas ir kita virusai pavyzdžiui, rinovirusai) yra painiojamas su gripu.
Gripas ir peršalimas, nors abu turi panašius simptomus, skiriasi ta prasme, kad juos sukelia skirtingi virusai.
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 virusas accumulating mutations (change in its DNR struktūra) per tam tikrą laikotarpį, kuris sukelia paviršiaus baltymų prigimties pokyčius. Visa tai apsunkina vakcinos nuo jų kūrimą, kuri užtikrintų ilgalaikę apsaugą. Paskutinę 1918 m. Ispanijos gripo pandemiją, kuri nusinešė milijonus žmonių, sukėlė gripas arba gripo virusas. Tai skiriasi nuo koronavirusų.
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 koronavirusai is normally limited to cold symptoms only and rarely made anyone seriously sick. However, there were some virulent forms of koronavirusai 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 koronavirusas.
Paskutinysis variantas of koronavirusas, the novel koronavirusas (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 virusas 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 koronavirusas reportedly underwent changes in its genome that made it into a highly virulent variant, responsible for the current pandemic.
Bet kas galėjo sukelti tokį drastišką antigenų poslinkį, dėl kurio SARS-CoV-2 tapo toks virulentiškas ir užkrečiamas?
Mokslo bendruomenėje sklando kelios teorijos, rodančios SARS-CoV-2 kilmę3,4. Proponents of man-made origin of the virusas 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 nes jei žmonės sukurtų virusas 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 virusas.
Be as it may, the fact of the matter remains that a certain almost innocuous virusas 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 evoliucija?
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Nuorodos:
- Padron-Regalado E. Vakcinos nuo SARS-CoV-2: Kitų koronaviruso padermių pamokos [paskelbta internete prieš spausdinimą, 2020 m. balandžio 23 d.]. Užkrėsti 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. 2019 m. naujojo koronaviruso kilmė ir evoliucija, Klinikinės infekcinės ligos, 71 tomas, 15 leidimas, 1 m. rugpjūčio 2020 d., 882–883 puslapiai, DOI:https://doi.org/.1093/cid/ciaa112
- Morens DM, Breman JG ir kt., 2020. COVID-19 kilmė ir kodėl tai svarbu. Amerikos tropinės medicinos ir higienos draugija. Prieiga internete: 22 m. liepos 2020 d. DOI: https://doi.org/10.4269/ajtmh.20-0849
- York A. Naujasis koronavirusas skrenda iš šikšnosparnių? Nat Rev Microbiol 18, 191 (2020). DOI:https://doi.org/10.1038/s41579-020-0336-9
- Andersen KG, Rambaut, A., Lipkin, WI et al. Proksimalinė SARS-CoV-2 kilmė. Nat Med 26, 450–452 (2020). DOI: https://doi.org/10.1038/s41591-020-0820-9.
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