Wednesday, August 03, 2022

Scientists see COVID’s origin in Wuhan market

Since the emergence of COVID-19, a question has obsessed many: where did it come from?

That question – and the fact the virus was first detected in the city of Wuhan, home of the Wuhan Institute of Virology – has sparked geopolitical convulsions and a fracturing of faith in science, not to mention a thousand anonymous Twitter-sleuth accounts.

Meanwhile, a group of scientists has been working on their own parallel investigative effort. With a pair of articles published in Science last week (you can read them here and here), they say they are at the end of their search.

The virus almost-certainly jumped from wildlife into humans in the Huanan Seafood Wholesale Market in Wuhan, the papers argue. The authors have even found the most likely section of the market. They have old photos of caged raccoon dogs – known carriers of COVID-19 – being sold there.

“The siren has definitely sounded on the lab leak theory,” says Professor Edward Holmes, a world-leading viral evolution expert based at the University of Sydney and co-author on both the papers. “In terms of what we can reasonably do, with the available science and the science we’ll get in the foreseeable future, I think we’re at the end of the road frankly. There’s not a lot more to mine.”

Professor Dominic Dwyer, director of public health pathology in NSW and a member of the World Health Organisation (WHO) team that travelled to Wuhan last year to investigate the origins of the virus, agrees.

“That’s what we thought originally back when we did the first report. This is yet another brick added to the wall of information around zoonotic infection.”

Twin strains

When COVID-19 first emerged in Wuhan, two distinct viral lineages were spotted, separated by two small changes in genetic code. They were detected a week apart in late December 2019.

The team behind the Science papers used computers to simulate the most likely sequence of events that would produce two viruses circulating at the same time.

They found it is exceedingly unlikely that a single virus would jump into humans and quickly split into two distinct variants.

Far more likely, was that the virus had been circulating in animals for long enough to split into multiple variants, two of which then jumped separately into humans. Multi-virus jumps have been seen when COVID-19 jumped from minks on Dutch farms to humans, and when SARS and MERS also jumped into humans.

If the COVID-19 virus originated in a lab, as some conspiracy theories suggest, you’d expect a single introduction into humans – rather than two distinct viral lineages. And both strains were found in samples taken from Huanan market. “That, I think, is pretty good evidence,” says Dwyer.

Lab-leak advocates argue that Huanan is a perfect super-spreader site. Maybe a scientist from the Wuhan Institute of Virology shopped there and spread the bug?

The Science papers show that 155 COVID cases in December 2019 were strongly clustered in the suburbs around the market – including cases with no known link to the market.

If the virus emerged from the Wuhan Institute of Virology, wouldn’t early cases cluster around there? Wouldn’t an infected scientist have passed on the virus while walking to work? “You wouldn’t expect to find the virus around a not-very-well-visited animal market in a different part of the city,” says Holmes.

And the papers show Huanan is hardly the perfect superspreader site that some suggest.

It turns out the market is a small and relatively obscure shopping spot. By reviewing social media check-in data, the team deduced that 70 other markets in Wuhan had more visitors than Huanan. Of 430 identified possible super-spreader sites in Wuhan, such as shopping malls, supermarkets and schools, the Huanan market was among the least visited.

“It’s like going to Coles in Bendigo on a wet Wednesday afternoon. It’s not a thriving mass of humanity,” says Holmes.

Further evidence: no COVID-19 has been detected among tens of thousands of blood donations made in Wuhan between September and December 2019, nor in thousands of samples taken from people hospitalised between October and December with influenza-like illnesses.

“What are the odds that two lineages escape from the lab and both make their way into the market and both cause superspreader events? It’s ridiculous. There is no way that can happen,” says Holmes.

We know now that COVID-19 moves easily among many species of animals, including raccoon dogs – but also badgers, hares, rats and foxes, all observed being sold live at the market in 2019.

Raccoon dogs were supplied to the market by a network of farms in western Hubei province, the Science papers note. Western Hubei is known for its extensive network of caves filled with Rhinolophus bats, which carry coronaviruses similar to the one that causes COVID-19.

“Raccoon dogs are a suspect,” says Holmes, but not the only one. “I think, strongly, there are a whole bunch of animals out there who have viruses like this that we have not sampled yet.”

Compare the theories

Theory one: Two closely related versions of a virus emerge at the same time in people who live near or work in a small market selling wildlife. The market sells animals known to both carry the virus and to be farmed near bats that carry similar viruses. We detect those viruses on cages in the market’s wildlife section.

We know from past experience viruses can jump from animals to humans at wildlife markets. And we don’t have any evidence of the virus spreading anywhere else in Wuhan before it was in the market.

Compare this to the lab-leak theory. No one has ever been able to prove COVID-19 – let alone a twin strain – was ever at the Wuhan Institute of Virology. There’s no epidemiological evidence that the virus was spreading near the institute.

“There’s no emails. There’s no evidence in any of the science. There’s absolutely nothing,” says Holmes.

Lab-leak proponents have now turned to trying to find malfeasance in the articles’ peer review process, of all places. Holmes doubts the conspiracy theorists will ever be convinced. “Even if the Chinese do let us in the lab, people would say ‘aha, but they’re covering it up’,” he says.


Sun key to vitamin D as pills prove worthless

The biggest study in the world into vitamin D supplements has found the pills do not prevent bone fractures and are unlikely to provide the same benefits as obtaining the vitamin from the sun.

About one-third of Australians are vitamin D-deficient, and many have been advised by their doctor to supplement with vitamin D pills, the biggest-selling supplement in the country.

A US study published in the New England Journal of Medicine suggests it would be far better to expose the skin to some sunlight every day instead.

The large study known as Vital, which involved 26,000 mid-life men and women, found vitamin D pills provide little benefit to most people. The headline finding was that vitamin D supplements do not prevent osteoporosis and were found not to prevent bone fractures even in people who already had bone thinning.

Vitamin D in the body plays a role in helping the gut absorb calcium, which strengthens bones.

Researchers on the study also found that vitamin D supplements did not provide the benefits of vitamin D obtained from sunlight, which include the prevention of cancer, prevention of heart disease, improvements in brain function and protection of the joints and eyes.

The NEJM published an editorial along with the study findings recommending people stop taking vitamin D supplements.

The author of the editorial was Steven Cummings, who is a research scientist at the California Pacific Medical Centre Research Institute.

“Providers should stop screening for 25-hydroxyvitamin D levels or recommending vitamin D supplements and people should stop taking vitamin D supplements in order to prevent major diseases or extend life,” Dr Cummings said.

“The trials show they have no benefit, even in people with vitamin D deficiency.

“With very few exceptions, such as those in nursing homes deprived from sun and ordinary diets, everyone gets enough vitamin D to maintain the functions and balance they need.”

You can also obtain vitamin D from foods including oily fish, eggs and red meat.

University of South Australia professor Elina Hypponen, who has extensively studied Vitamin D, said the US study did not include people who were truly vitamin D-deficient, and that such people would be likely still to obtain benefit from taking the ­supplements.

“If you can get vitamin D naturally and safely from the sun without risk of sunburn, then you don’t need to think about supplements,” Professor Hypponen said.

“But in situations where people are seriously vitamin D-deficient, then vitamin D supplements are sometimes necessary.”

The Vital study was funded by the US National Institutes of Health and began after an expert group examined the health effects of vitamin D supplements and found little evidence.

The Vital study reinforces a ­series of other research projects that have cast doubt on the efficacy of vitamin D supplements.




No comments: