The search continues for the origins of the virus that causes COVID-19and the pathway that it took to leap from animals to humans, wreaking havoc across the globe, infecting more than 129 million people, and killing more than 2.8 million.
Earlier this week, the World Health Organization released a report from a team of international researchers that traveled to China to investigate four possible scenarios in which the SARS-CoV-2 virus might have caused the initial outbreak. In the days since, however, world governments have expressed concern that the investigators lacked access to complete data, while scientists say that the report has shed little light on how the virus got jumpstarted.
Thats unsurprising given that it typically takes years to trace a virus back to its rootsif its possible at all, says Angela Rasmussen, a virologist at the Center for Global Health Science and Security at Georgetown University Medical Center. But in this case, she says, I think we do have enough evidence to say that some are more likely than others.
In the report, the team found that the virus most likely jumped from one animal to another before making its way to humans. They also looked at evidence supporting theories that the virus passed into humans directly from an original host animal, or that it traveled through the supply chain for frozen and refrigerated foods. In addition, the team addressed the possibility that the virus accidentally leaked from a laboratory in Wuhana scenario they determined is extremely unlikely.
Heres a look at the evidence the report lays out for each of the four theoriesand what experts make of them as possible origin stories for SARS-CoV-2, the virus that causes COVID-19.
WHO ASSESSMENT: possible to likely
The first origin story for SARS-CoV-2 is simple: It suggests that the virus started out in an animalprobably a batthat came into contact with a human. Boom, infected. At that point, the virus immediately began to spread to other humans.
The WHO report cites strong evidence showing that most coronaviruses that infect humans come from animals, including the virus that caused the SARS epidemic in 2003. Bats are thought to be the most likely culprits, as they host a virus that is genetically related to SARS-CoV-2.
The report acknowledges the possibility that the virus spread to humans from pangolins or minks. But David Robertson, head of viral genomics and bioinformatics at the University of Glasgow, says the WHO joint team sampled many animal species beyond bats for the report. The analyses points to bats as the reservoir species.
So what you have to worry about then is how did it get from bats to humans? Robertson says. Did somebody go into an area, get infected, and then get a train to Wuhan?
Direct transmission between bats and humans is possible: Studies have shown that people who live near bat caves in southern Chinas Yunnan Province have antibodies to bat coronaviruses. But most humans generally dont spend much time around bats, unless they are bat scientists (who typically wear protective equipment). So its unclear why, if the virus jumped from bats directly to humans, the first outbreak would have occurred in Wuhan, a thousand miles away from the bat caves of Yunnan.
Furthermore, the report notes that it would take decades for even the closely related bat coronavirus to evolve into SARS-CoV-2. Since scientists havent found a bat virus that would provide the missing link, the WHO team assessed this theory as possible to likely.
WHO ASSESSMENT: likely to very likely
In the absence of a smoking gun showing that bats passed the virus directly to humans, scientists believe the more likely theory is that the virus first traveled through another animal, such as a mink or a pangolin. Unlike bats, these animals have regular contact with humansparticularly if theyre being raised on a farm or trafficked in the illegal wildlife trade.
If the virus jumped first to another animal, that might also explain how it adapted to be harmful to humansalthough Robertson says that the virus likely wouldnt have had to change much. Genomic analyses suggest that SARS-CoV-2 is a generalist virus rather than one specifically adapted to humans, explaining why it can easily jump among pangolins, mink, cats, and other species.
The WHO report points out that this is the path that previous coronaviruses have taken to infect humans. The SARS virus, for example, is thought to have passed from bats to palm civets before causing a human epidemic in 2002. Meanwhile, the virus that causes MERS has been found in dromedary camels throughout the Middle East.
Daniel Lucey, an adjunct professor of infectious diseases at Georgetown University Medical Center, says that the similarities between SARS-CoV-2 and its relatives SARS and MERS is a compelling argument that it might have started out the same way.
Now we have three coronaviruses that cause pneumonia and systemic illness and death, he says. Past is prologue.
But, if the theory holds true, its not clear what that intermediary animal might have been for SARS-CoV-2. The WHO team analyzed samples from thousands of farmed animals across China, all of which tested negative for the virus. Lucey argues that the WHO team didnt adequately test Chinas farmed minkone of the suspected intermediariesbut Rasmussen says the report itself acknowledges that it only scratches the surface.
Thats a fraction of the animals that are farmed or captured or transported for this purpose in China, she says. I think we havent done anywhere near enough sampling.
Theres a popular perception that we need some kind of justice or explanation and somebody needs to answer for this pandemic. But the real reason why we need to figure out the origin is so that it can inform our efforts to prevent another pandemic like this from happening.
ByAngela RasmussenVirologist at the Center for Global Health Science and Security at Georgetown University Medical Center
WHO ASSESSMENT: possible
Another theory holds that the virus may have come to humans through whats known as the cold chainthe supply line for distributing frozen and refrigerated foods. In this scenario, the virus might have actually originated outside of China but was imported either on the surface of food packaging or in the food itself.
This theory gained traction last summer after a couple of outbreaks in China, and there has since been some evidence suggesting that pathogens can survive longer in cold temperatures.
Still, while the cold chain might have played a role in new outbreaks, scientists say theres little reason to believe that it was the source of the pandemic. Theres no direct evidence that SARS-CoV-2 is responsible for foodborne outbreaks, while Rasmussen notes that COVID-19 rarely spreads through surfaceswhich was good news for those weary of wiping down their groceries.
Its not impossible, she says. You cant rule it out. But I dont think the evidence base is particularly strong for that.
Rasmussen says a more plausible way that the virus might spread through the food chain would be through wildlife thats farmed for human consumption. But, she points out, that bleeds over into the territory of the theory for an intermediate host.
Some critics claim that this theory is a red herring to push suspicion from China and onto other countries. Lucey considers this pathway the least likely of the four the joint team identified, arguing its implausible that the virus would have stayed viable on the packaging for as long as it took to import from Europe or elsewhere. He also questions why these infections would have turned up in Wuhan and nowhere else.
To me, its beyond far-fetched, he says.
WHO ASSESSMENT: extremely unlikely
The most controversial hypothesis for the origin of SARS-CoV-2 is also the one that most scientists agree is the least likely: that the virus somehow leaked out of a laboratory in Wuhan where researchers study bat coronaviruses. Originally promulgated by former President Donald Trump and his administration, this theory suggests that perhaps a researcher was infected in the labaccidentally or otherwiseor manipulated a coronavirus strain to create SARS-CoV-2.
Although there have been laboratory leaks in the past, the WHO report points out that theyre rare. The main evidence it cites to support this theory is the fact that researchers at the Wuhan Institute of Virology have sequenced the bat coronavirus straincalled CoV RaTG13, which is 96.2 percent similar to SARS-CoV-2, and its closest known relativeas part of their effort to prevent zoonotic viruses from spilling over to humans. A laboratory run by the Wuhan Center for Disease Control and Prevention has also worked with bat coronaviruses.
But thats just about the only evidence that supports this hypothesis. The WHO report says there is no record that any Wuhan laboratory was working with a virus more closely related to SARS-CoV-2 before the first cases of COVID-19 were diagnosed in December 2019, nor did any laboratory staff report any COVID-like symptoms suggesting that they had been infected. But scientists point out that the evidence both for and against the lab leak hypothesis is thin.
Lucey believes the lab leak theory is plausible, though less likely than zoonotic transmission, given the lack of evidence. He points out that there was no forensic investigation of the labs in Wuhan, and he questions why the WHO authorized the team to investigate the lab at all without the mandate to conduct such an investigation or team members with the subject-matter expertise to carry it out.
Theres not really any way to prove or disprove the lab leak theory based on whats been presented in this report, Rasmussen agrees, noting that to put the matter to rest there would need to be a forensic audit of lab records to look for the ancestral virus to SARS-COV-2. But my opinion is that the lab leak theory, while not impossible, is less likely to be the explanation.
Rasmussen explains that theres no evidence that SARS-CoV-2 is the result of genetic manipulation, nor is it likely that it could have been created by accident. Its incredibly difficult to culture a virus thats strong enough to cause human infections from a bat sample, she says. Meanwhile, similar viruses commonly occur in nature, making that the far likelier source.
Robertson says that supporters of the lab leak theory argue that SARS-CoV-2 has traveled too quickly and efficiently through the human population to be natural in origin. But if the virus is a generalist, as genomic studies show, he says its not surprising that it is so effective at infecting humans.
I think the evidence is pretty good that it didnt have to change much to be successful in humans, he says.
Although the WHO report may not have shed much light on the origins of SARS-CoV-2, Robertson says this is just the beginning of what can sometimes be a long process. But he says theres a public health imperative now to launch more rigorous follow-up studies.
Theres a virus somewhere out there thats very close to SARS-CoV-2, he says. That seems to be the bit thats terrifying.
Rasmussen says that the WHO report lays out a roadmap for further studies to discover the origins of the virus. It recommends better surveillance of captive and farmed animals to determine potential reservoir or intermediate hosts, as well as more sampling among batsboth in China and beyond, as there is also evidence of related coronaviruses circulating in regions such as Southeast Asia. The report also recommends in-depth epidemiological studies of the first COVID-19 cases.
Understanding how an outbreak got started helps scientists and governments pinpoint how to strengthen protectionswhether thats more rigorous surveillance for infections in animals and the food chain, or tighter biosafety protocols in laboratories.
Theres a popular perception that we need some kind of justice or explanation, and somebody needs to answer for this pandemic, Rasmussen says. But the real reason why we need to figure out the origin is so that it can inform our efforts to prevent another pandemic like this from happening.
See the article here:
We still dont know the origins of the coronavirus. Here are 4 scenarios. - National Geographic
- Sputnik V, a host of coronavirus mutations and a rocket stack - Nature.com - April 14th, 2021
- Coronavirus in Michigan: Heres what to know April 14, 2021 - WDIV ClickOnDetroit - April 14th, 2021
- COVID-19 patients with sedentary habits more likely to die, finds study - The Hindu - April 14th, 2021
- 2 more Mainers die and another 571 coronavirus cases are reported across the state - Bangor Daily News - April 14th, 2021
- Coronavirus vaccination required to attend Buffalo Bills games, officials say - WFLA - April 14th, 2021
- Six new coronavirus cases reported on Nantucket Wednesday - The Inquirer and Mirror - April 14th, 2021
- Coronavirus tally: Global cases of COVID-19 top 136.7 million and U.S. death tally heads toward 563,000 - MarketWatch - April 14th, 2021
- UJAR 2021: The impact of coronavirus on universal jurisdiction - FIDH - FIDH - April 12th, 2021
- Coronavirus in Michigan: Heres what to know April 10, 2021 - WDIV ClickOnDetroit - April 12th, 2021
- Pa. announces all adults will be eligible for a vaccine on Tuesday; Philly faces steep drop in Johnson & Johns - The Philadelphia Inquirer - April 12th, 2021
- Coronavirus hospitalizations plunge among Ohios most vaccinated age groups - cleveland.com - April 12th, 2021
- India's daily virus infections are world's highest but crowds gather for festival - Reuters - April 12th, 2021
- Tweaked COVID vaccines in testing aim to fend off variants - WKBN.com - April 12th, 2021
- COVID-19 in South Dakota: 187 total new cases; One new death; Active cases at 2,425 - KELOLAND.com - April 12th, 2021
- Madison Township bar accused of coronavirus health order violation - News-Herald.com - April 12th, 2021
- More than 2 million COVID-19 shots given in Alabama - FOX10 News - April 12th, 2021
- One new coronavirus case reported on Nantucket Sunday - The Inquirer and Mirror - April 12th, 2021
- Mens curling world championship playoffs on hold due to coronavirus - Home of the Olympic Channel - April 11th, 2021
- Coronavirus in Oregon: 761 new cases reported in highest daily count since February - OregonLive - April 11th, 2021
- Health experts give safety advice to all Missourians about receiving the coronavirus vaccine - ABC17NEWS - ABC17News.com - April 11th, 2021
- Teenagers and the coronavirus vaccine: What parents are asking - cleveland.com - April 11th, 2021
- NSU Spartans respond to two public health threats: racism and the coronavirus - WAVY.com - April 11th, 2021
- VERIFY: Are you better off if you get COVID-19 now versus a year ago? - KING5.com - April 11th, 2021
- City-County Health moving COVID-19 vaccinations to new location - Wyoming Tribune - April 11th, 2021
- Active cases of coronavirus rise in Ulster and Dutchess counties; Dutchess offers free rides to vaccination sites - The Daily Freeman - April 11th, 2021
- With California set to fully reopen by June 15, experts say its unlikely another coronavirus surge will overwhelm hospitals - KTLA Los Angeles - April 11th, 2021
- Hawaii DOH investigating 2 sports teams halted due to coronavirus - KHON2 - April 9th, 2021
- Ohio coronavirus case rate increases to highest point in a month; 52 counties on red alert - cleveland.com - April 9th, 2021
- Nearly half of new coronavirus infections nationwide are in just five states - WJW FOX 8 News Cleveland - April 9th, 2021
- Coronavirus or allergies? Heres how to tell the difference. - SILive.com - April 9th, 2021
- After coronavirus pause, UND football returns to practice in hopes of making a playoff run - Grand Forks Herald - April 9th, 2021
- Virus Variants Threaten to Draw Out the Pandemic, Scientists Say - The New York Times - April 9th, 2021
- What Washington parents should know about COVID-19 vaccines for 16- and 17-year-olds - KING5.com - April 9th, 2021
- The American Rescue Plan: Coronavirus State and Local Fiscal Recovery Funds - AAF - American Action Forum - April 9th, 2021
- Coronavirus tally: Global cases of COVID-19 top 132.5 million and U.S. death toll above 556,000 - MarketWatch - April 7th, 2021
- COVID-19: What you need to know about the coronavirus pandemic on 6 April - World Economic Forum - April 7th, 2021
- More transmissible coronavirus variants on the rise in Pa. and N.J., as case counts keep going up - The Philadelphia Inquirer - April 7th, 2021
- What you need to know about the coronavirus right now - Reuters - April 7th, 2021
- COVID-19 update: Active coronavirus cases grow within Humble ISD this week - Houston Chronicle - April 7th, 2021
- Jon Husted to meet with Asian American neighbors over coronavirus tweet: Overnight News Links - cleveland.com - April 7th, 2021
- Coronavirus: L.A. County surpasses 5 million vaccinations with 406 new cases and 23 new deaths reported as of April 6 - The Daily Breeze - April 7th, 2021
- Middle East And Africa Struggle To Shake Off Economic Effects Of Coronavirus Pandemic - Forbes - April 7th, 2021
- Brazil's COVID-19 death surge set to pass the worst of record U.S. wave - Reuters - April 7th, 2021
- How Vaccine Hesitancy Could Prolong the Pandemic - Healthline - April 7th, 2021
- 45 Pa. counties have substantial spread of COVID-19; positive test rate rises for third week in a row - PennLive - April 7th, 2021
- Trudeau says Canada is facing 'very serious' third wave of COVID-19 pandemic - The Union Leader - April 7th, 2021
- 293 infected in new coronavirus outbreaks at 75 schools, says Michigans April 4 school outbreak report - MLive.com - April 7th, 2021
- Will fourth wave of COVID-19 in East spread to California? - Los Angeles Times - April 5th, 2021
- Coronavirus in Michigan: Heres what to know April 3, 2021 - WDIV ClickOnDetroit - April 5th, 2021
- These are the latest COVID numbers in Georgia for April 4, 2021 - 11Alive.com WXIA - April 5th, 2021
- How Long Does Immunity from COVID-19 Vaccination Last? - Healthline - April 5th, 2021
- Brazils coronavirus nightmare: Bolsonaro is more isolated than ever - Financial Times - April 5th, 2021
- Two new coronavirus cases reported on Nantucket Sunday - The Inquirer and Mirror - April 5th, 2021
- Russia Claims to Be the First Country to Develop Coronavirus Shots for Animals - The New York Times - April 5th, 2021
- Coronavirus Tennessee: Cases, deaths and hospitalizations across the state in April - WATE 6 On Your Side - April 5th, 2021
- Analysis-In mutant variants, has the coronavirus shown its best tricks? - Reuters - April 5th, 2021
- Coronavirus cases are up in Ohio and reopening is in jeopardy - Mahoning Matters - April 5th, 2021
- Pennsylvania will study the impact of COVID on learning and teaching - The Mercury - April 5th, 2021
- Fauci Expects Surge In Vaccinations To Keep A 4th Coronavirus Wave At Bay - NPR - April 3rd, 2021
- Hawaii to receive $32M in federal aid to support coronavirus vaccinations - KHON2 - April 3rd, 2021
- Rick Carlisle cleared to rejoin Mavericks after coronavirus scare - The Official Home - Mavs.com - April 3rd, 2021
- These are the latest COVID numbers in Georgia for April 1, 2021 - 11Alive.com WXIA - April 3rd, 2021
- Undetected Coronavirus Variant Was in at Least 15 Countries Before its Discovery - UT News - UT News | The University of Texas at Austin - April 3rd, 2021
- India great Sachin Tendulkar admitted to hospital with coronavirus - The Guardian - April 3rd, 2021
- Coronavirus in Minnesota: 12 more deaths; hospitalizations on the rise - MinnPost - April 3rd, 2021
- 14-year-old Milwaukee boy dies of coronavirus complications - WXOW.com - April 3rd, 2021
- Moderna and Pfizer COVID-19 vaccines may block infection as well as disease - Science News Magazine - April 3rd, 2021
- Reopening last summer may have led to 45 coronavirus deaths a Scripps study shows - CBS News 8 - April 3rd, 2021
- Here's a list of the latest COVID data for Georgia: April 2, 2021 - 11Alive.com WXIA - April 3rd, 2021
- Coronavirus (COVID-19) Update: FDA Continues to Advance Over-the Counter and Other Screening Test Development - FDA.gov - April 1st, 2021
- Coronavirus tally: Global cases of COVID-19 near 129 million and U.S. death toll tops 552,000 - MarketWatch - April 1st, 2021
- Coronavirus in Michigan: Heres what to know April 1, 2021 - WDIV ClickOnDetroit - April 1st, 2021
- India Reports Its Highest Daily Number Of COVID-19 Deaths So Far This Year - NPR - April 1st, 2021
- Can I still spread the coronavirus after I'm vaccinated? - WBNG-TV - April 1st, 2021
- COVID-19 Confirmed As 3rd Leading Cause Of Death In US Last Year : Coronavirus Updates - NPR - April 1st, 2021
- Region may be experiencing third wave of coronavirus infections | INFORUM - INFORUM - April 1st, 2021
- Wednesday's coronavirus updates: 'We have the B117 variant in our community. It is more infectious, and it is causing more serious illness in younger... - April 1st, 2021
- UK COVID variant is now the predominant strain in many parts of the country | Connect the Dots - KHOU.com - April 1st, 2021
- Coronavirus surge could be worse than the last for the Americas: PAHO - Reuters - April 1st, 2021
- Gov. DeSantis to get COVID-19 vaccine this week - WFLA - April 1st, 2021