Thread by @firefoxx66

Great question! Now, the actual naming of viruses & syndromes is above my pay grade 😉 (& much discussion about #COVID19 #SARSCoV2 & #hCoV19 has already happened!), but let's explore how SARS-1 & SARS-2 are related - & who else is in the family!

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https://twitter.com/jjswin/status/1261592279296421888

The 'CoV' in #SARSCoV2 stands for 'Coronavirus' - that's a big, diverse family of viruses. SARS-CoV-2 is a member of the 'Betacoronavirus' genera (group) (there's also Alpha- Gamma- & Delta- groups... very creative naming 😆)

Let's have a look at some of the group...

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There are plenty of Betacoronaviruses, but we can focus on a few of the stars of the family. @trvrb put together a run showing MERS (Middle-eastern Respiratory Syndrome), SARS-1, SARS-2 & two seasonal coronaviruses, OC43 & HKU1 (they return each year)

nextstrain.org/groups/blab/be…

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You can see that #SARSCoV2 fits well in this family. It's more distantly related to MERS & the 2 seasonal coronaviruses, & considerably closer to SARS-1. There are a few other (mostly animal) coronaviruses scattered throughout (in grey).

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But we can also zoom in on that lower part of the tree - how are SARS-1 & SARS-2 connected? They look pretty directly related from the first tree, when compared to other members of the Betacoronavirus group! Are they?

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Here's a run of SARS-CoV-1 & #SARSCoV2, with just very close nearby viruses. If you go back and forth between the two pictures, notice the X-axis (genetic diversity) has changed a lot - the 'SARS' tree is much more closely related!

nextstrain.org/groups/blab/sa…

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However, though SARS-CoV-1 & #SARSCoV2 are related, zooming in makes it clear that SARS-CoV-2 is not directly descended from SARS-1. They're members of the same family, but not ancestor & offspring - they are distinct! 🧬

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The blue viruses you see around them are 'SARS-like' coronaviruses, mostly collected from animals. This shows that very similar viruses to both SARS-1 & SARS-2 are present in the wild, circulating in animal hosts. Both SARS were due to spillover events from animals -> humans.

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If we zoom in on the #SARSCoV2 part of the tree, notice we can see the much-discussed closest relative to SARS-CoV-2 - a sequence from a bat (slightly confusingly) called Yunnan/RaTG13 🦇. We can also see nearby sequences from pangolins 🦫 (still no pangolin emoji!).

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Important to note - though Yunnan/RatG13 is very closely related to #SARSCoV2, it's still pretty distant relative to the diversity we see *within* SARS-CoV-2.

Here it looks like a flat line! That's because *all* the SARS-COV-2 viruses circulating are incredibly similar!

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This is why when you ask those of us working on #SARSCoV2 #COVID19 how many 'strains' there are - we say one! In the larger viral picture, the SARS-CoV-2 viruses are incredibly similar!

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Of course, when you go to nextstrain.org/ncov, you've 'zoomed in' another level (only SARS-2) - so that small amount of diversity fills the screen - it looks like much more!

But, as is so often in life, it's all relative 😉

(Note the x-axis scale change from prev pic!)

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This thread doesn't nearly cover all that can be said about Coronaviruses, Betacoronaviruses, or even SARS-like coronaviruses - but I hope it helps clarify how SARS-CoV-1 and #SARSCoV2 are related, & how they are different!

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