How Three Types Of The New Coronavirus Swept Across The Globe

Forster et al/PNAS 2020

Like a team of sleuthing detectives, scientists at the University of Cambridge have tracked the genetic mutations of the novel coronavirus to see how COVID-19 rapidly swept across in the globe. 

Their research has revealed three branches on the family tree of SARS-CoV-2, the coronavirus responsible for the respiratory infection COVID-19, which they call A, B, and C. 

Type A is the “original human virus genome” and is the closest type of coronavirus to the one seen in both bats and pangolins, two species suspected of playing a role in the transmission of SARS-CoV-2 from animals to humans. It appears that A emerged in the human population in the Chinese city of Wuhan in Hubei province, but it wasn’t actually the city’s predominant virus type. 

A gave rise to B, which was prevalent in patients from Wuhan, as well as much of China and East Asia. Type B then mutated to create Type C, the variant seen across much of Europe, most notably among the early patients from France, Italy, Sweden, and the UK. Mainland China appeared to have no cases of this variant, although it was also found in Singapore, Hong Kong, South Korea, and other parts of East Asia. 

A "map" showing the transmission routes using phylogenetic networks. Forster et al/PNAS 2020

As reported in the journal Proceedings of the National Academy of Sciences, the team of forensic archaeologists reached these conclusions by studying the first 160 complete virus genomes to be sequenced from human patients. By looking at the different mutations found within these virus genomes, they created a "map" of the different lineages found across the world, which you can see above. 

“Phylogenetic network analysis has the potential to help identify undocumented COVID-19 infection sources, which can then be quarantined to contain further spread of the disease worldwide,” geneticist Dr Peter Forster, lead author from the University of Cambridge, said in a statement

“The viral network we have detailed is a snapshot of the early stages of an epidemic, before the evolutionary paths of COVID-19 become obscured by vast numbers of mutations,” Forster added. “It’s like catching an incipient supernova in the act.” 

If you’re wondering where the US fits into this map, the researchers show a large number of both type A and B viruses were found in patients from the US, as well as few type C viruses. This suggests most cases in the US might have a direct link to the types found in China and East Asia. However, other preliminary studies have painted a different picture. A new study on the pre-preprint server medRxiv – which is still awaiting peer review – suggests that the coronaviruses types found in New York City, the worst affected area in the world, can be traced back to travelers from Europe, not China.

As ever with this constantly evolving outbreak, it might be some time until the "fog of war" dissipates and scientists are able to work out the full picture.

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