Christian Drosten is director of the Institute of Virology at the Charité Berlin. He works and researches coronaviruses and was 2003 one of the discoverers of the Sars virus.
We are currently experiencing evolution live: A coronavirus, which probably originates from another mammal species, is trying to colonize humanity. How does such a virus do that, Mr. Drosten?
You could say they have taken good care: Coronaviruses are broad Range of genetic variants represented across many mammalian species. This is a pool of possibilities that is always available and tries its luck with new hosts. And sometimes it just works.
And why are they so variable? Do they mutate particularly quickly?
On the contrary. They are much calmer than, for example, flu viruses. These are also RNA viruses, but they constantly change their genes and thus the surfaces that are built according to these templates. This is different with the corona viruses. Their genes and thus their external structure are comparatively resistant to change.
The virus RNA must be copied in the host cell to generate new viruses. There are automatically reading errors. What do the corona viruses do differently?
You have a repair system with you that corrects these errors. Your genes change anyway, but more slowly – and more sensibly. If you rely on reading errors, you accept that many of the changes created are stillbirths. If, on the other hand, you have a correction system, there is another mutation maker: as soon as they share a host cell, the genes of the different coronaviruses combine with each other. The mutations that come out of it are much more meaningful, the snippets involved have already been tried out, so to speak. Over time, a relatively large pool of stable variants accumulates.
Coronaviruses are not restricted to mammals, they are common to all possible vertebrates, even in the biologically very distant fish. Does this mean that these viruses are as old as the first vertebrates?
This is conceivable. But they could also have opened up these different hosts afterwards. These are very long periods of time that we are talking about. It is difficult to understand.
You are working on “evolution cards” of corona viruses yourself. Together with Australian and English colleagues, you collected coronaviruses from Western European and East Asian rodents and read out their genetic information in the laboratory. What can you conclude from this?
We can use this to estimate when the first corona virus entered this group. And whether it then developed linearly with the rodent species or whether there were frequent leaps in style. In this case, all viruses were due to a single ancestor …
… who must have colonized the primeval mouse, so to speak …
Yes. It also looks as if his descendants jumped back and forth between the host species quite often.
And what are you allowed to do? Do you think you can draw conclusions for today from the RNA sequences?
If you do it right, you can learn something for future pandemics. How viruses behave after an art jump, for example. The Sars virus had 2002, in the first few weeks of the outbreak, a certain protein that probably made the virus more contagious. Then this protein suddenly disappeared.
First of all, it is the opposite of what you would assume. Was the protein useful for the virus?
Nevertheless, it is logical. When a virus opens up a new host type, it is as if a single breeding pair of birds and its offspring colonize a new island on which this type does not yet exist. We know that fitness can drop compared to the original population because random, unfavorable genetic variants can also prevail. The Sars virus was just like the offspring of such a scattered breeding pair. Where they settled, there were no other representatives of their kind with whom they had to prove themselves in competition. By chance, some of them lost the valuable protein. However, they continued to spread – while the dangerous viruses probably died out in isolation hospitals.
But now we are in the middle of the current situation , They explain from the perspective of an evolutionary researcher why it is essential to isolate infected people when a new virus occurs: to send the breeding birds to the island.
Exactly. The new virus types should not have a chance to build up a human-sized, competitive population, also because they could remain or become more dangerous.
At the moment you can hear everywhere that the new corona virus is not as dangerous as Sars, but it is very likely even before the first symptoms is contagious. And maybe even after the sick are well again. Does isolation still make sense?
Yes, this virus is surprisingly different from the Sars pathogen at the time. I see this with great concern, but also optimism: the virus is probably better transmitted because it makes people less sick.
People who fear that they have contracted the corona virus have to go to the same facilities in Berlin, where travelers can get their vaccinations. An ideal international hub for the viruses. Is there a lack of planning?
I see no problem there at the moment. At the moment, a lot of people think they are suspicious cases without being. So you will most likely not infect the travelers. And nobody is haphazard: there is the Infection Protection Act with a clear reporting chain and there are also pandemic plans. Be sure that there is a task force in the health department that is preparing this. The normal waiting rooms as the first point of contact are part of these plans. There is no other way in Germany, everything is organized decentrally.
The WHO has just declared an emergency. Does this help to better control the situation internationally?
This helps to synchronize and justify international decisions. Travel warnings can then be given more easily.
And for the German situation?
Only indirectly. We have most of it in our own hands. And I actually see a – tiny – gap here. According to current law, doctors only have to report confirmed cases. That is too late for an overview of the situation. But this is currently being changed: suspicious cases will soon be subject to notification.