bloomberg | More than a year after Covid-19 touched off the worst pandemic in more than a century, scientists have yet to determine its origins. The closest related viruses to SARS-CoV-2 were found in bats more than 1,000 miles from the central Chinese city of Wuhan, where the disease erupted in late 2019. Initially, cases were tied to a fresh food market and possibly the wildlife sold there. Other theories allege the virus accidentally escaped from a nearby research laboratory, or entered China via imported frozen food. Amid all the posturing and finger-pointing, governments and scientists agree that deciphering the creation story is key to reducing the risk of future pandemics.
1. Why don’t we know where it came from?
Where, when and how a pathogen crosses the species barrier and begins spreading in humans can be difficult, if not impossible, to pinpoint. Although SARS-CoV-2 is genetically similar to coronaviruses collected from a type of bat, it may have followed a long and convoluted path to Wuhan, a city of 11 million people. Scientists are tracing the earliest known cases to try to establish how they were infected, but the trail backward largely goes cold in early December 2019. Where a new disease starts spreading isn’t necessarily where it spilled over from the animal kingdom to infect the first human. HIV, for instance, is thought to have originated in chimpanzees in southeastern Cameroon, but didn’t begin spreading readily in people until the 1920s, when it reached the city of Kinshasa, hundreds of miles away. Scientists reported that finding in 2014, some three decades after the AIDS pandemic was recognized.
2. Who’s looking?
The World Health Organization was asked in May to help with the research, and a team of 17 international scientists, including one based in the U.S., concluded a four-week joint mission with 17 researchers from China in early February. Their findings are slated to be released in March. Other groups, including an expert panel convened by the medical journal The Lancet called the Covid-19 Commission, are also
3. What do we know so far?
Not much. Bats are the source of two coronaviruses that caused lethal outbreaks in people during the past two decades -- severe acute respiratory syndrome (SARS) and Middle Eastern respiratory syndrome (MERS) -- and the flying mammals are considered the reservoir host for SARS-CoV-2 as well as a plethora of other viruses. (A reservoir host is an animal that harbors a pathogen but isn’t sickened by it.) After SARS-CoV-2 emerged, Shi Zhengli, a virologist who heads a group that studies bat-borne coronaviruses at the Wuhan Institute of Virology, identified three closely related viruses collected during the previous 15 years. The closest, which is about 96% identical to SARS-CoV-2, was isolated from swabs and fecal material from Rhinolophus affinis, a species of horseshoe bat, in the southern Chinese province of Yunnan in 2013. Some researchers have linked that particular virus to a mineshaft in Mojiang county in Yunnan, where six men contracted a pneumonia-like disease in 2012 that killed three of them. Although SARS-CoV-2 and the virus from Yunnan may share a common ancestor, they’re not sufficiently similar to indicate SARS-CoV-2 was derived from the Yunnan virus. Sampling of bats in Hubei, the province of which Wuhan is the capital, haven’t found any positive for the pandemic strain. Coronaviruses sharing certain genetic features with SARS-CoV-2 have been found in other Rhinolophus bat species and pangolins, a scaly, ant-eating mammal, elsewhere in Asia, highlighting the broad distribution of related coronaviruses that may have contributed to SARS-CoV-2’s evolution. That’s led to multiple hypotheses for how and where it emerged.
probing the virus’s origins.