From coronaviruses to coronaviruses

Abstract

The official history of the discovery of human coronaviruses dates back to 1965, when the first coronavirus B814, which has now been lost, was isolated on the human embryonic tracheal organ culture from the nasal swabs of a patient with acute respiratory disease. However, this time point can only be an intermediate stage on its long evolutionary path. Paleovirological studies have shown that coronaviruses could have appeared as early as in the Stone Age — in the Upper Paleolithic era, and East Asia is considered as their place of origin — a region that is well known to virologists as the source of many highly pathogenic influenza viruses and new coronaviruses, such as SARS-CoV, MERS-CoV, and SARS-CoV-2. This makes us take a different look at the seeming “innocence” of seasonal coronaviruses that circulated before 2002, when a human pathogenic virus appeared that caused SARS. This also fits well into the assumption about the coronavirus nature of the 1889 Russian flu pandemic. Today, four seasonal and three new, pathogenic for human coronaviruses are known. Two seasonal coronaviruses (229E and NL63) belong to the genus Alphacoronavirus, 2 others (OC43 and HKU1) and three new coronaviruses (SARS, MERS and SARS-CoV-2) belong to the genus Betacoronavirus. In this review, we have focused on the “extreme points” — seasonal coronaviruses and pandemic SARS-CoV-2. We attempted to draw an analogy between them and identify their main distinguishing features. From the viewpoint of epidemiology and clinic, common what they have is only the airborne transmission route, characteristic of all respiratory viruses, and the ubiquitous distribution, the nature and intensity of which were not markedly affected by the influenza epidemics/pandemics. Seasonal coronaviruses continued to circulate even during the COVID-19 pandemic, when the majority of other respiratory viruses had largely disappeared. Significant differences between seasonal coronaviruses and SARS-CoV-2 can be traced in the symptoms, severity and pathogenesis of the diseases they cause. At the structural level, they have a lot common features including taxonomic proximity, morphology, structure, physicochemical properties of virions, genome organization, the main stages of virus replication, etc. What made SARS-CoV-2 such aggressive? The few differences in the size of viral particles and viral genome that have been identified to date, the use or not of hemagglutinin esterase to penetrate into a sensitive cell, attachment to different cell receptors cannot underlie a prominent difference in severity of the infection caused by seasonal or pandemic coronavirus. Most likely, that these differences are based on delicate molecular mechanisms that have yet to be discovered.