Remember a few months ago when news reporters were comparing SARS-CoV-2 (the virus that causes COVID-19) to a simple cold or the flu? No one wanted to believe that the new novel coronavirus emerging out of China was as deadly or contagious as reported. How could it be? New illnesses and viruses emerge on an almost yearly basis, but the medical and economic carnage that SARS-CoV-2 has caused is unprecedented.
SARS-CoV-2 has changed all our lives, in large part, due to its highly contagious nature. But, what makes this coronavirus strain so much more transmissible than other variations like SARS-CoV-1 or MERS? Researchers from Cornell University believe they’ve found the answer to that nagging question.
After closely analyzing SARS-CoV-2’s genetic lineage, the study’s authors say that SARS-CoV-2 combines the deadliness of the first SARS virus that emerged in China in 2003 with the contagiousness of HCoV-HKU1, a super contagious human coronavirus strain that hardly causes any symptoms at all. Unsettlingly, SARS-CoV-2 is a mixture of the worst that both of these strains had to offer.
“It’s got this strange combination of both properties,” explains Gary Whittaker, professor of virology in Cornell’s College of Veterinary Medicine, in a university release.
SARS-CoV-2, just like other coronaviruses, enters a new host’s cells through its spike protein. The research team at Cornell discovered a new structural loop within SARS-CoV-2’s spike protein that houses four amino acids that are quite distinct from any other known human coronavirus. Professor Whittaker believes that this structural loop and sequence of four amino acids are what make SARS-CoV-2 so contagious.
“The prediction is that that loop is very important to transmissibility or stability, or both,” he adds.
There’s been a whole lot of debate and theories regarding where SARS-CoV-2 came from. According to professor Whittaker, recent research did identify a bat in China carrying a coronavirus strain with a very similar structural loop to SARS-CoV-2, but the amino acid sequence wasn’t the same. However, the study’s authors compared the SARS-CoV-2 structural model with the structures of other coronaviruses found in animals, and say they were able to confirm that SARS-CoV-2 did originate in bats.
Other studies have pointed to pangolins as being the animal originators of the virus, but the team at Cornell says there isn’t enough evidence to support that theory.
“How SARS-CoV-2 got into humans is still unclear,” Whittaker says.
The discovery of this new amino acid sequence suggests, according to Whittaker and his team, that there was another intermediate animal host that carried SARS-CoV-2 before this virus jumped to humans.
Meanwhile, the research team has also concluded that, besides primates, cats, ferrets, and mink are the animals most at risk of carrying SARS-CoV-2. For the virus to infect a new organism, its spike protein must bind with a receptor located on a host cell’s surface. Cats’ receptors are very similar to humans. Feline SARS-CoV-2 infections, though, are very mild and rarely show themselves at all. Moreover, there is no evidence that cats can infect humans.
That being said, researchers think studying and analyzing feline coronaviruses may provide more useful information and data that can be used to stop SARS-CoV-2.
“We are keeping an open mind to see if similar things may happen in cats that already are now happening in humans,” Whittaker concludes.
To beat SARS-CoV-2, we have to fully understand it. There are still many questions, but these findings, in all likelihood, have provided at least one major answer.
The full study can be found here, published in the Journal of Molecular Biology.