SARS-CoV-2 probably originated in bats, but how it passed to people has been the subject of intense speculation and is now being investigated by the World Health Organization.
Experts from the World Health Organization (WHO) arrive in China today to carry out a long-anticipated investigation into the origins of the coronavirus.
Ten researchers with expertise in virology, ecology and public health are hoping to answer key questions about how and when SARS-CoV-2 first infected people.
Although more than a year has passed since the first reported case of coronavirus in China in December 2019, experts still do not know exactly when or where the virus emerged.
While much of the evidence so far points to horseshoe bats in China, ongoing research – such as a recent study suggesting coronavirus was circulating in Italy as early as November 2019 – are a reminder that infectious disease outbreaks are often more complicated than they seem.
If we want to better understand how and when people get infected in the first place, for both now and future outbreaks, experts say it's important to trace the virus back to its starting point.
In the beginning of an outbreak, this can help slow the spread of a disease before it spirals out of control. If every case can be identified, every contact traced and every potential carrier quarantined, pathogens can be halted.
But even after that initial containment period is lost, as in the case with SARS-CoV-2, finding the origin of a disease can give us useful insights, says Naomi Forrester-Soto, a virologist studying vector-borne diseases at Keele University in the UK.
"The more we understand about how diseases emerge, the better we can predict and control them," Forrester-Soto told DW.
That does not necessarily mean identifying coronavirus "patient zero," which many experts, such as Forrester-Soto, no longer think is possible.
Rather, it's about finding out in which species this virus is most likely to have emerged and in what circumstance it crossed over from animals to humans. This may help inform how we change our behavior toward certain animals – both wild and farmed, says the virologist.
In the aftermath of the first Ebola epidemic in west Africa, which killed more than 11,000 people between 2014 and 2016, experts tracked the chain of disease back to the first victim: a two-year-old called Emile Ouamouno, who died in a remote part of Guinea in December 2013.
One of those researchers, wildlife veterinarian and microbiologist Fabian Leendertz, who helped trace the initial Ebola infection back to bats that lived in a hollow tree where children played, joins the WHO team on its mission in China.
Leendertz's research helped experts understand how the disease had spread and the risk posed by close contact with these animals.
While identifying that first case was important in curbing Ebola, the detective work was made much easier because of how lethal and unique Ebola is, says Martin Beer, a professor of virology at the Federal Research Institute for Animal Health in Germany.
It's possible the first people infected with coronavirus showed no symptoms at all. That, says Beer, has made piecing together the coronavirus puzzle, "very, very difficult."
"With respiratory diseases it is nearly impossible — it could be influenza or any other cold. [Coronavirus] patient zero themself probably does not know that they were, in fact, infected," Beer told DW.
Although the first coronavirus case was detected in Wuhan, China in December 2019 and much of the speculation regarding its starting point has centered around the likelihood it passed from bats to humans through another species sold at a wet market there — it is still possible it originated somewhere else.
Chinese authorities have also stated it is possible that the virus could have emerged in another country entirely. Although scientists have not given this theory much credence, the WHO team have repeatedly said they are keeping an open mind as to all potential starting points.
Pangolins were initially suspected as intermediate hosts for SARS-CoV-2, but were not listed as being sold at the Huanan wet market in Wuhan
According to Beer, it is likely that the origins of the virus are in China, as "that is where we saw the first cluster of infections." But that does not necessarily mean the first spillover occurred at the wet market, or even in Wuhan.
Samples collected and stored after the 2013 SARS-CoV-1 outbreak show the RaTG13 bat virus circulating in horseshoe bats of China's Yunnan province has a 96% similarity to the new coronavirus that causes COVID.
"That the virus originated from a bat seems to be more or less clear, but the known viruses from bats in China are too distant to have caused a direct spillover infection," Beer said.
The question is, he says: are there viruses circulating in bats that are closely enough related to SARS-CoV-2 to have caused infection, or was there another animal in the mix that passed this virus on to humans? If the latter is the case, that could explain how the virus ended up in Wuhan, Hubei province, nearly 2,000 kilometers away from Yunnan province.
This is a crucial line of inquiry that the WHO team will be pursuing, Beer says.
The WHO has emphasized it is not looking to point the finger.
"We are looking for the answers here that may save us in the future, not culprits and not people to blame," Mike Ryan, director of the WHO’s Health Emergencies Program, told a press conference on Monday.
Minks are known carriers of coronaviruses, but researchers still don't know which animal passed SARS-CoV-2 onto humans
"We can blame climate change, we can blame policy decisions made 30 years ago," he said. "If you're looking for someone to blame, you can find people to blame on every level of what we're doing on this planet."
When thinking about the origin case in the context of the coronavirus, Forrester-Soto says, instead of asking who, it’s more helpful to ask — how and why?
“The emergence of a pandemic-level coronavirus really shouldn’t have surprised anybody," Forrester-Soto said, pointing out that scientists have been warning about the health risks of increased encroachment into natural areas for decades.
"We know that human disturbance of ecosystems contributes to the emergence of pandemics. There are basically no undisturbed places left on the planet," she said.