Coronavirus: The science of how it can jump species

Viruses have one goal: to reproduce. And they don’t generally care where they do it.

Passengers from China arrive at Ninoy Aquino International Airport in Manila. The Philippines and other Asian countries are on high alert following the outbreak of a new strain of coronavirus from Wuhan. Picture: Getty Images

Viruses have one goal: to reproduce. And they don’t generally care where they do it.

They can do it in bats, they can do it in humans, they can do it in snakes — and it’s even better, from their point of view, if they can do it in all three.

Jumping the species barrier, however, as happened with the coronavirus, is difficult — especially so if, as some scientists now believe, the last host is a distantly related species like a snake.

To successfully live in one species, you have to find a way to evade its immune system, to hijack its cells to your own ends and then also find ways to make that species spread you — through sneezing, or sex or some other method. This means that diseases are often very well adapted to one host.

However, diseases also reproduce rapidly, which means they can evolve rapidly.

All it takes is a few mutations that are advantageous (again, very much from the point of view of a virus) and a disease can find a home in a new species.

A few more mutations, and it can use this foothold to become successful and spread.

To make such a sequence of beneficial mutations is extremely unlikely for one virus, but becomes a lot more likely when you realise there are trillions of them.

This is why many human diseases originated in animals, with a whole new wave dating to the domestication of livestock. A bacterium, Yersinia pestis, lives in ­rodents largely unnoticed. When it started infecting humans as well, it became something that we did notice: the Black Death.

What is strange about the findings on the new coronavirus is that if the scientists doing the genetic analysis are correct, it probably spread first from bats, then into snakes — an animal with a physiology very different from bats — then into humans.

It is one thing to catch a disease from a primate, or even a rat — both are mammals. It is quite another to catch one from a cold-blooded reptile whose last common ancestor with us lived some 300 million years ago.

The Times