Article by Debasish B. KrishnatreyaPh.D. Scholar Department of Botany Gauhati University, Guwahati
The most trending topicof discussion in the year 2020 has been none other than the deadly pandemic, Covid‑19. It has already spread across more than 215 countries, and as on 9th July 2020, 12,198,686 cases of infection and 552,791 deaths due to coronavirus have been recorded all over the world (https://www.worldometers.info/coronavirus/). Coronavirus Study Group of the International Committee on Taxonomy of Viruses (ICTV-CSG) has provided a taxonomic appellation to the causal organism of Covid-19 as SARS‑CoV‑2 (Severe Acute Respiratory Syndrome-Coronavirus‑2) on 11th February 2020.
One of the main questions that scientists and socialists have been arguing over is regarding the originof SARS-CoV‑2. It is a very commonnotion that the disease did originate in Wuhan, China, possibly from the live animal markets such as the Huanan seafood wholesale market. According to certain speculations, consumption of bat meat by the Chinese people was a major cause of spread of this novel coronavirus to humans. Some studies have reported that pangolins (an endangered animal, whose scales are used in traditional Chinese medicines, and also frequently devoured as food in China) may also be a potential source of this coronavirus outbreak. Infact, coronaviruses from both bats as well as pangolins have been reported and their genomic sequences have also been made available in the public domain. Some scientists believe that the novel coronavirus (SARS-CoV‑2) has evolved from either the bat coronavirus (RaTG13) or the pangolin coronavirus. According to a second school of thought, the SARS-CoV‑2 has evolved from the SARS-CoV or the MERS-CoV, two other coronavirus species, which had earlier spread pandemics among human race. SARS-CoV caused the first pandemic of the 21st century in 2002-2003, spreading across 29 countries, with most cases recorded from Hong Kong and China. It originated due to zoonotic transmission of a novel coronavirus in Guangdong province of China, eventually infecting many countries and registering a total number of 8096 cases, with 774 deaths. Middle East respiratory syndrome (MERS) was also a viral respiratory disease caused by a novel coronavirus (MERS‑CoV) that was first identified in Saudi Arabia in 2012.
For understanding the possible explanations of these arguments, one must know about the basic #pathogenesis patterns of #coronaviruses. #Morphologically, coronaviruses consist of spike proteins all over their membrane. The receptor binding domains(RBD) of these spike glycoproteins bind to host receptors to infect them. Both SARS-CoV and SARS-CoV‑2 utilise the human ACE2 (angiotensin converting enzyme) receptor to infect the respiratory tracts, wheras MERS-CoV utilises the human #DPP4(dipeptidyl peptidase 4) receptor. The multiple sequence alignments of the RBDs of spike #glycoproteins, revealed that #SARS-CoV‑2 exhibits close affinities with #pangolin and bat coronaviruses (90% and 89% respectively), as compared toSARS-CoV and #MERS-CoV.Around 5 to 6 amino acids, which are crucial for RBD domains to bind with #humanACE2 receptor, have been found to vary between SARS-CoV‑2 and SARS-CoV. This explains as to why both these related viruses show differences in their degree of affinity in binding to ACE2 receptors. Moreover, when comparing the whole genome sequences, bat #coronavirus shows 96% similarity with SARS-CoV‑2, whereas SARS-CoV and MERS-CoV exhibit only 79% and 51% homology.These are the primary scientific explanations of why pangolins and bats are considered as the ancestral source of Covid 19 virus, instead of SARS-CoV and MERS-CoV. However, in a major contrast, researches have also suggested that in spite of greater degree of genomic similarities between them, bat coronavirus is reportedly unable to utilize the same ACE2 receptor as SARS-CoV‑2 for initializing the pathogenesis in human hosts.
#Amino acid sequencealignments of RBDs of spike glycoproteins belonging SARS-CoV‑2 and four other coronaviruses from which SARS-CoV‑2 is speculated to have evolved.
All said and done, it is thus clear that the research regarding pathogenesis patterns,genomic aspects and the life cycle of corona virus is still at an incomplete stage. As a result, development of effective vaccines and medications against this virus has become an out-and-out challenge for the researchers. We hope that all the confusions and contradictions regarding the action and affinity of corona virus are cleared very soon, and success in developing effective vaccines against the virus is achieved. Mankind has to find suitable ways of coping up with such disasters in future, so that the human civilization can continue to flourish!!