Saturday, March 21, 2020

It's possible that COVID-19 didn't come from a Wuhan animal market after all

Many people have been asking "where did COVID-19 come from?", partly out of curiosity, but also partly in search of a scapegoat, some one or something to blame.
Most people are aware that the disease was first noted in the city of Wuhan in China's Hubei province. The general view is that it began in the Huanan wild animal market (or "wet market") in Wuhan, also somewhat euphemistically described as a seafood market, and that it was passed to humans from some kind of wild animal there.
Further back than that, though, things get murky. Genetic analysis of the virus shows a strong (96%) similarity to viruses found in Rhinolophus affinis bats (Intermediate Horseshoe Bats), a common species in southeast Asia, and it seems likely that this bat (or a very similar species) served as the reservoir host for the virus. However, the spike protein used for binding in these bat viruses is not compatible with human cells, and so direct transmission from bats to humans is very unlikely (and bats are not sold in wet markets anyway).
So, an intermediary animal is proposed, in the same way as a similar species of horseshoe bat was responsible for the 2003 SARS pandemic, and the intermediary animal in that case was the small wild cat called the civet. The most likely intermediary animal for the transmission of COVID-19 was thought for a time to be the Malayan pangolin, a rare endangered animal sold illegally in Chinese wet markets for its supposed traditipnal medicine benefits. Pangolins also carry viruses that are very similar to the SARS-CoV-2 virus that causes COVID-19, and these protein spikes ARE compatible with human cells.
So, bats via pangolins, then? Well, maybe, but maybe not. The identification of the pangolin may have been based on a miscommunication, and more recent research has thrown the pangolin theory into some doubt. New theories suggest that some species of turtles may be more likely intermediaries.
Anyway, maybe we don't need to pin it down to one specific animal. Surely, it is enough to know that Asian wet markets are the culprit for most of these kinds of epidemics, and that they should be shut down.
That may be true, but now it is not even entirely clear that the first cases of COVID-19 do in fact stem from the Wuhan market at all. Cases dating back to November 17th 2019 or even earlier are coming to light, and it's possible that an unexplained spike of unusual pneumonia cases in December may actually have been COVID-19. .
The first ever reported case ("Patient Zero"?), dating back to December 1st, was an elderly man suffering from Alzheimer's disease, and he lived "four or five buses" away  from the market and was so, and was so sick that he hardly ever went out. In fact, 13 of the first 41 official cases were probably not related to the Wuhan market, which was closed down on January 1st 2020
Does all this matter? Possibly not, but it does muddy the water somewhat for future analyses. And we may have to get used to the idea that we may never have a clear smoking-gun patient-zero situation on which to hang a hat. And that wet market in Wuhan was certainly instrumental in spreading the disease so quickly in the first instance.

In a Nature interview witb George Gao, Director-General of the Chinese Center for Disease Control and Prevention, and the man at the forefront of the remarkably successful Chinese response to the COVID-19 outbreak in China, he certainly seems to be of the opinion that, whether or not the Huanan market was the original source of the outbreak, it was definitely an important amplifying factor in the early days. So, let's move to clamp down once and for all on live animal markets anyway (and not just in China).

No comments: