Where Did SARS-CoV-2 Come From?

SARS-CoV-2 backbone genome closely resembles that of a bat coronavirus
depiction of virus with a bat hanging
(Coronavirus Today)

No matter which social media network you visit, there’s bound to be a discussion of coronavirus disease 2019 (COVID-19). These conversations generally lead to the origin of the SARS-CoV-2 coronavirus. 

According to the NIH’s Director’s Blog by Dr. Francis Collins on March 26, 2020, a new study offers scientific evidence that this new coronavirus arose naturally.

The reassuring findings are the result of genomic analyses conducted by an international research team, partly supported by NIH. 

In their study published in the journal Nature Medicine on March 17, 2020, Kristian Andersen, Scripps Research Institute, La Jolla, CA; Robert Garry, Tulane University School of Medicine, New Orleans; and their colleagues used sophisticated bioinformatic tools to compare publicly available genomic data from several coronaviruses, including the new one that causes COVID-19 disease.

The researchers began by homing in on the parts of the coronavirus genomes that encode the spike proteins that give this family of viruses their distinctive crown-like appearance.

All coronaviruses, such as SARS and MERS, rely on spike proteins to infect other cells. 

But, over time, each coronavirus has fashioned these proteins a little differently, and the evolutionary clues about these modifications are spelled out in their genomes.

The genomic data of the new coronavirus responsible for COVID-19 show that its spike protein contains some unique adaptations. 

One of these adaptations provides the special ability of this coronavirus to bind to a specific protein on human cells called angiotensin-converting enzyme (ACE2). 

The coronavirus that causes SARS in humans also seeks out ACE2.

Existing computer models predicted that the new coronavirus would not bind to ACE2, as well as the SARS virus.

However, to their surprise, the researchers found that the spike protein of the new coronavirus actually bound far better than computer predictions.

This is likely because of natural selection on ACE2 that enabled the virus to take advantage of a previously unidentified alternate binding site. 

Researchers said this provides strong evidence that the new virus was not the product of purposeful manipulation in a lab. 

In fact, any bioengineer trying to design a coronavirus that threatened human health probably would never have chosen this particular conformation for a spike protein.

The researchers went on to analyze genomic data related to the overall molecular structure, or backbone, of the new coronavirus. 

Their analysis showed that the backbone of the new coronavirus’s genome most closely resembles that of a bat coronavirus discovered after the COVID-19 pandemic began. 

However, the region that binds ACE2 resembles a novel virus found in pangolins, a strange-looking animal sometimes called a scaly anteater. 

This provides additional evidence that the coronavirus that causes COVID-19 almost certainly originated in nature. 

If the new coronavirus had been manufactured in a lab, scientists most likely would have used the backbones of coronaviruses already known to cause serious diseases in humans.

So, what is the natural origin of the novel coronavirus responsible for the COVID-19 pandemic? 

The researchers don’t yet have a precise answer. But they do offer two possible scenarios.

In the 1st scenario, as the new coronavirus evolved in its natural hosts, possibly bats or pangolins, its spike proteins mutated to bind to molecules similar in structure to the human ACE2 protein, thereby enabling it to infect human cells. 

This scenario seems to fit other recent outbreaks of coronavirus-caused disease in humans, such as SARS, which arose from cat-like civets; and MERS, which arose from camels.

The 2nd scenario is that the new coronavirus crossed from animals into humans before it became capable of causing human disease. 

Then, as a result of gradual evolutionary changes over years or perhaps decades, the virus eventually gained the ability to spread from human-to-human and cause serious, often life-threatening diseases.

Either way, this study leaves little room to refute a natural origin for COVID-19. 

And that’s a good thing because it helps us keep focused on what really matters: observing good hygiene, practicing social distancing, and supporting the efforts of all the dedicated healthcare professionals and researchers who are working so hard to address this major public health challenge.

SARS-CoV-2 outbreak news published by Coronavirus Today.