According to a recently published article on Nature, with the WHO team investigating the origins of Covid-19, there are still few key questions unanswered about when, where and how the pandemic began.
Investigating COVID-19 origins
The World Health Organization (WHO) team investigating the origins of the COVID-19 pandemic concluded that the coronavirus probably originated in bats and passed to people through an intermediate animal. But fundamental questions remain about when, where and how SARS-CoV-2 first infected people.
- Was The Virus Circulating in Wuhan Before the First Known Cases?
- Was The Virus Spreading in People Outside China Before December 2019?
- What Was The Role of the Huanan Market?
- Did Frozen Wild-Animal Meat Have a Role in the Early Spread of the Virus?
- Was The Virus Circulating in Animals in China Before the Pandemic?
Was the virus circulating in Wuhan before the first known cases?
To trace the virus’s origin, it’s crucial to pin down exactly when the first cases occurred in people. The WHO team established that the first person known to have COVID-19 was an office worker in Wuhan with no recent travel history, who began showing symptoms on 8 December 2019. The virus was probably spreading in the city before that because it was well-established by later that month.
Survey of patient reports
Yet the evidence of earlier spread has proved elusive. Researchers in China conducted an extensive survey of patient reports from hospitals in Wuhan made between October and December 2019 and identified fewer than 100 people who had symptoms of COVID-19.
Antibodies with SARS-CoV-2
They then tested the blood of 67 of those people for antibodies generated by past infection with SARS-CoV-2 but found none. This suggests there wasn’t a large cluster of infections before December or an unusual spike in deaths in the surrounding province of Hubei.
Scientists in China should also search for evidence of past infection in some 200,000 archived samples currently held at the Wuhan Blood Center and in other regions across China, says team member Dominic Dwyer, a medical virologist at New South Wales Health Pathology in Sydney, Australia. This would show whether the virus was spreading in the general population in China — not just among people who went to health facilities — before December 2019.
Was the virus spreading in people outside China before December 2019?
Researchers in Europe have reported finding antibodies against SARS-CoV-2 in samples taken at blood banks from November 2019 onwards.
Ben Embarek says this doesn’t necessarily suggest the virus originated in Europe but supports the idea that it was spreading in Wuhan before the first known cases. “Wuhan at that time was a very well-connected international city with direct flights to the entire planet on a daily basis. So if it was circulating in Wuhan, it could easily have been brought to other parts of the world through travelers, and circulating again, undetected, in different regions,” he says.
Still, he recommends that the blood samples from Europe be retested to confirm that they indicate cases of COVID-19. Some of them, from Italy and France, are already being reanalyzed, he says.
What was the role of the Huanan market?
The intermediate animal that passed the virus from bats to people has not been identified, but researchers think it might be a wild species that is sold as food in ‘wet markets’, which typically sell live animals. Early in the pandemic, investigators homed in on the Huanan Seafood Market in Wuhan, because it sold fresh and frozen animals and many of the earliest infections were in people who had visited it.
But the lead went cold when other early cases were found that were not associated with the market. Viral material was identified in drains and sewage at the market, but none was found on any animal carcasses.
Nguyen-Viet says the team identified ten stalls selling wildlife, either wild or farmed, that could have carried the virus into the market from farms in southern China. Some wild animals sold for meat, such as rabbits and ferret-badgers, are susceptible to SARS-CoV-2 or the related virus that causes severe acute respiratory syndrome (SARS). When the team interviewed the first person known to have COVID-19, he mentioned that his parents had visited a local community wet market, says Daszak.
Did frozen wild-animal meat have a role in the early spread of the virus?
The WHO team concluded that it’s most likely the virus jumped from live animals to people, but Ben Embarek says it is possible the virus entered the Huanan market through infected frozen wild animals from farms in southern China, and then sparked an outbreak.
Daszak wonders whether frozen ferret-badgers sold at the market could have carried the virus. “These were carcasses skinned at the market, not just cubes of meat in a plastic packet,” he says.
Was the virus circulating in animals in China before the pandemic?
To establish which animal passed the virus to people, researchers need to find evidence of the virus in that species. Researchers in China tested some 30,000 wild, farmed and domestic animals in 2019 and 2020 but found no evidence of active or past SARS-CoV-2 infection, except in some cats in Wuhan in March 20205.
However, Ben Embarek says these surveys were not representative of China’s overall animal population, and that many more animals need to be tested for traces of infection, particularly on wildlife farms. “The amount of testing that’s been done is not sufficient to say, in any way, that wildlife farms were not carrying the virus,” says Daszak.
The explosive way in which the outbreak took off in Wuhan in December suggests that the virus was probably introduced once, through the wildlife trade, says Daszak. He says future testing should focus on farmed wild animals.
Did you subscribe to our daily newsletter?
It’s Free! Click here to Subscribe!
Source: Nature
