Looking to SARS & MERS for Covid origins

Before we explore COVID19s origins further and what theses genetic analyses are, and aren't telling us it's helpful to step back a bit and consider the other earlier examples of coronaviruses that have made the leap into humans so we can ask whether COVID19 is any different. The first encounter was back in 2002 with the coronavirus that became known as SARS, short for severe acute respiratory syndrome, which spread around the world from China and circulated for about a year infecting thousands of people and causing hundreds of deaths. The other, which came a bit later, is called MERS - middle Eastern respiratory syndrome, which was first picked up in that geography. Matt Ridley, such journalist and coauthor of the book "Viral -  the search for the origin of COVID19" explains...

Matt - So the world first became aware of SARS in February 2003, but it quickly became apparent that people had been picking it up as far back as November the previous year. By May 2003, scientists had worked out that the early cases were mostly people who were handling food or were chefs, and that certain animals seemed to be carrying the virus, in particular palms civets. And by the summer of 2004, testing wildlife had revealed that bats were carrying a virus that was ancestral to both the civet version and the human version. MERS was first detected in 2012 and at first there was something of a mystery as to where it was coming from - there was only one case initially. But fairly quickly, within a few months, it was clear that the people who were handling camels were picking up the virus more than other people. And so camels were tested and found to be carrying the virus. It was later determined that the ancestral virus lives in bats. So probably the camels had picked it up from bats, although no direct evidence for that has ever been found.

Chris - While these outbreaks occurred in two geographically distinct locations and a decade apart, the origins of both outbreaks do share remarkable similarities.

Matt - Bat to animal to person in both SARS and MERS was very quickly established.

Chris - Infections that jump from one species to another called zoonosis. And although viruses carry their own genetic code, they are too small to carry along the machinery that they also need to copy themselves. It's a bit like having an Ikea instruction manual without the flat pack. The genetic code is useless for growing new viruses, unless it can sneak into warehouses - like our cells, that are packed with all the tools and raw materials that they need to copy themselves. But when they do break in, viruses grow at an alarming rate.

Julia - But growing fast comes at a cost. Just as if you try to type really fast, you'll make more typos. And when viruses copy their genetic material, spelling mistakes called mutations crop up in these copies. And this can alter the properties of the virus.

Chris - For instance, these changes can facilitate a virus being able to jump from one species into another. Normally viruses are very good at breaking into cells of a specific animal because they have keys designed to open those warehouses to unlock all the materials that they need to replicate. But if mutations arise that alter the properties of the virus and reshape its viral keys, then they can unlock cells of other organisms, enabling the virus to jump the species barrier and exploit a whole new group of animals, including us.

Julia - And in the case of SARS-Cov-2, the patterns of previous outbreaks directed the initial search.

Matt - The authorities immediately assumed it was through the food chain, just like SARS had been. They closed down the Huanan seafood market. A number of the early cases had connections to that market, but not all of them. And they tested the animals they found in the market, they tested the food in the market and they tested the surfaces and door knobs, countertops, and sewage. They found the virus on the surfaces, but they did not find it in any samples for sale in the market. And in fact, over the succeeding months, the Chinese authorities tested 80,000 animals all across China in an attempt to find an infected animal, as they very quickly found in the case of SARS. No ancestral version of the virus has been found in an animal apart from in human beings.