The pandemic that emerged in Wuhan, China, in December 2019 has affected all of humanity and specifically the scientific field at many levels. The SASR-CoV-2 coronavirus is named after the associated disease (Severe Acute Respiratory Syndrome Coronavirus 2), but it is not the first species of coronavirus to cause respiratory disease in humans. The global and coordinated scientific effort has revealed many key aspects of this coronavirus, but the origin and how it jumped to humans continues to raise some questions.
Animal origin, but with unknowns
During these more than two years of the pandemic, the different hypotheses about the origin of SARS-CoV-2 have been the focus of study, analysis and investigation, but also of hoaxes and conspiracy theories. It is not surprising that, in the face of a global health crisis and the unknown cause of the pathogen, fear and lack of scientific knowledge have given rise to more or less credible theories about its origin. Numerous independent investigations from different countries (including the United States CIA) have made their own estimates and analyzes based on the evidence collected on the first cases detected in Wuhan . Although no investigation has been able to provide irrefutable evidence of the origin of SARS-CoV-2, all agree that the most likely origin is a natural jump from an animal to humans. But, what evidence do we have to argue this origin as the most probable?
A study published in the journal Nature has shown that coronaviruses present in bats and related to SARS-CoV-2 are capable of infecting human cells. This evidence has been obtained thanks to experiments using widely used cell cultures together with an analysis of the genome of several coronaviruses present in bats, pangolins and humans. This study supports the origin of a coronavirus variant halfway between SARS-CoV-2 and the most similar one detected in Rhinolophus affinis , commonly known as the horseshoe-faced bat.
In this same line we find another study recently published in the journalGenome Biology and Evolution,where haveconducted a comparative analysis of various types of coronavirus present in different types of bats in Asia.This type of analysis, known as phylogenetic, is like trying to draw a family tree of SARS-CoV-2 based on the features it shares or differentiates it from other coronaviruses. The results not onlyagain point to the coronavirus present in bats as the most likely candidate and closest to SARS-CoV-2, adding evidence to the natural origin of the pandemic, but also demonstrates the importance of this type of analysis in the future. Apparently, different coronaviruses have been evolving in regions of Asia during the last 100 years, giving rise to numerous variants that have been maintained in one region or another, using various species of bats as reservoirs. They have reached this conclusion by focusing on specific parts of the virus genome known as “hot spots”, where many mutations that have been selected over time have been concentrated. These hot spots represent molecules with special functions for the infection and/or propagation of the virus. Another reflection that the authors contribute in their study is the possibility thatAn intermediate species between the bat and the human is not necessary, since antibodies against coronavirus had been detected in rural populations of China.. If years before the pandemic caused by SARS-CoV-2, there were humans who presented elements of a response to coronavirus infection in the form of antibodies in the blood, these jumps may be more frequent than we think.
Could a new coronavirus appear?
Analysis of the appearance of a new zoonotic virus (which lives in an animal species other than humans) that mutates and jumps to humans, point to a low probability. However, phylogenetic studies have shown that there are a large number of viruses with the potential to infect human cells and about which we have little information . Two other coronaviruses have jumped to humans in recent decades: MERS and SARS-CoV. Some types of virus have higher mutation rates than others, and studying the mechanisms of cell entry in their reservoir animals can give us clues to assess the risk of infection in humans.
The case of coronaviruses seems more worrying due to the jumps observed in recent years and the presence of antibodies in a percentage of the population in Asia. However, it would not be surprising if another type of virus could jump to humans, especially considering the variables that affect the climate and exert pressure on animal behavior. For all these reasons, new phylogenetic studies of zoonotic viruses are measures recommended by the scientific and health community.
References:
Temam et al. 2022. Bat coronaviruses related to SARS-CoV-2 and infectious for human cells. Nature. doi: 10.1038/s41586-022-04532-4
Lytras et al. 2022. Exploring the Natural origins of SARS-CoV-2 in the Light of Recombination. Genome Biol Evol. doi: 10.1093/gbe/evac018
