Los coronavirus no son nuevos; estos son tan antiguos como cualquier otra cosa en el mundo y se sabe que causan resfriado común entre los seres humanos durante siglos. Sin embargo, su última variante, el 'SARS-CoV-2' actualmente en las noticias por causar COVID-19 la pandemia es nueva.
Often, common cold (caused by coronavirus así como de otros virus como los rinovirus) se confunde con la gripe.
La gripe y el resfriado común, aunque ambos presentan síntomas similares, son diferentes en el sentido de que son causados por virus diferentes en conjunto.
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 ADN estructura) durante un período de tiempo que provoca cambios en la naturaleza de las proteínas de superficie. Todo esto dificulta el desarrollo de vacunas contra ellos que puedan brindar protección de larga duración. La última pandemia de gripe española de 1918 que mató a millones de personas fue causada por la gripe o el virus de la influenza. Esto es diferente de los coronavirus.
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 coronavirus is normally limited to cold symptoms only and rarely made anyone seriously sick. However, there were some virulent forms of coronavirus 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 coronavirus.
La última variante of coronavirus, la novela coronavirus (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 coronavirus reportedly underwent changes in its genome that made it into a highly virulent variant, responsible for the current pandemic.
Pero, ¿qué pudo haber causado una deriva antigénica tan drástica que hizo que el SARS-CoV-2 fuera tan virulento e infeccioso?
Hay varias teorías circulando en la comunidad científica que apuntan al origen del 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 porque si los humanos crearan el 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 evolución?
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Referencias:
- Padron-Regalado E. Vacunas para el SARS-CoV-2: lecciones de otras cepas de coronavirus [publicado en línea antes de la impresión, 2020 de abril de 23]. Infectar 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.Origen y evolución del nuevo coronavirus de 2019, Clinical Infectious Diseases, Volumen 71, Número 15, 1 de agosto de 2020, Páginas 882–883, DOI:https://doi.org/.1093/cid/ciaa112
- Morens DM, Breman JG, et al 2020. El origen de COVID-19 y por qué es importante. La Sociedad Estadounidense de Medicina e Higiene Tropical. Disponible online: 22 de julio de 2020. DOI: https://doi.org/10.4269/ajtmh.20-0849
- York A. ¿El nuevo coronavirus huye de los murciélagos? Nat Rev Microbiol 18, 191 (2020). DOI:https://doi.org/10.1038/s41579-020-0336-9
- Andersen KG, Rambaut, A., Lipkin, WI et al. El origen proximal del SARS-CoV-2. Nat. Med. 26, 450-452 (2020). DOI: https://doi.org/10.1038/s41591-020-0820-9.
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