An interesting article in the Scientific American by Josh Fischman examines this issue.
So how the SARS-CoV-2 virus start?
In an interview with CNN that aired on March 28 a prominent scientist speculated, without evidence, that the origin was when the SARS-CoV-2 virus escaped from a laboratory in Wuhan, China, where the outbreak was first noticed. The virologist was Robert Redfield, a former director of the US Centres for Disease Control. But he added that ‘this is my own view, and only an opinion’.
Two days later, advocates of a different origin shared their view:
There was a wildlife spill-over, with a virus that started in bats in China.
A joint report from the WHO and the Chinese government speculated, again without direct evidence, that the bat virus went through other animals and ended up infecting humans.
There has been no evidence found that a coronavirus from the Wuhan lab has been experimented on to be more transmissible like SARS-CoV-2. This would have required the workers from the laboratory to be infected.
Likewise, a coronavirus has not been found in the wild that mutated to become similar to SARS-CoV-2 as it passed from other animals and then infected humans.
Both ideas are largely evidence-free at this point although they are both possible. However, they are not equally probable.
They differ in the number of events that could create each scenario.
Redfield’s lab leak idea relies on one event, or perhaps a small handful: a mistake in the lab.
The wildlife spill-over idea has millions of chances to occur.
Redfield’s speculation is that any virus that comes from animals and become so efficient at infecting humans had to have lab help to do so in one quick jump. However, this is a big assumption!
In fact, Redfield himself, in the same CNN interview, said he thinks the virus was circulating for months before we noticed it. That is not a quick jump. It is an extended time period that fits idea number two, the wildlife spill-over.
The idea holds that there are billions of bats in China, and millions of encounters every week amongst bats and other wild animals and, in some cases, humans. The virus therefore has many chances to jump.
In its original form, it is inefficient at replicating in people. It had millions of chances to get better at it before it infected the first human.
An opportunistic virus can infect these species which go out foraging and have numerous encounters with other animals, such as pangolins, badgers, pigs and many others.
Coronaviruses mix amongst bat colonies, giving them chances to re-sort their genes. They even mix amongst single bats: a bat has been observed harbouring several different coronaviruses.
These viruses have time, they do not take one jump but spend months moving from host to host, mutating as they go.
Once in people, virus versions which mutate improve their ability to infect human cells increasing their chance to replicate more often. They soon become good enough at infecting those cells and humans become noticeably sick, and then we finally notice a new disease. This happens in the same timeframe that Redfield says that the virus was circulating.
This can now be observed with the current SARS-CoV-2 virus. It is quickly gaining mutations that make it more infectious, and doing so within independent lineages across the globe. According to Adam Lauring of the University of Michigan, this is happening naturally because millions of infections around the globe have provided millions of opportunities for mutations. It is not happening because of a lab leak.
So which scenario is more likely?
Redfield’s lab leak, which relies on one speculative episode?
Or the notion of a wildlife spill-over, with a million or so chances to occur?
If you were playing a card game, would you put your money on the card that has only one chance of coming up or the card that has a million chances to show.
Both scenarios are possible, but one is a lot more probable.
This is the major reason most scientists are suggesting a wildlife spill-over. It does however matter a lot because knowing how a virus driven pandemic begins focuses our attention on preventing similar situations. There are many disease-causing viruses out there.
It also matters in another way, to stop speculation – sloppy Chinese scientists released a virus, which was common under the Trump administration, has fuelled a tremendous wave of anti-Asian racism in the United States, contributing to hundreds of acts of violence and terrorised communities. Hopefully the answer will become clear at some stage.
The London General Practice provides all forms of testing for COVID-19 including rapid antigen lateral flow, PCR testing, and all those required for travel including fit to fly, test for release and day two and day eight PCR COVID testing.
Dr Paul Ettlinger
The London General Practice