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At the end of December 2019, the Wuhan Municipal Health Commission reported cases of unidentified viral infection. pneumonia, which, along with other reports, alerted the World Health Organization (WHO) of a potential new health threat that has been identified as a coronavirus in January 2020 and was subsequently named SARS-CoV-2.
But it became clear that the virus appeared before the end of December 2019, possibly even months before. A joint WHO study by Chinese and international researchers identified 174 SARS-CoV-2 infections throughout December, with the first dating back to December 8. Although most researchers believe the virus first appeared in the fall or winter of 2019, it’s difficult to pinpoint the exact time without more data. Finding out when SARS-CoV-2 started to spread among people could help prevent or control future epidemics and pandemics providing insight into the kind of disease surveillance that would have been needed to prevent it, experts say.
By the time the virus was identified, it had already spread significantly and was more difficult to contain, said Sergei Pond, professor of biology at Temple University in Philadelphia. “You don’t want to wait eight weeks until you have a cluster of cases with unusual pneumonia,” Pond said. “You kind of want to have a surveillance system where you get it really early on.”
Related: 7 facts about the origin of the new coronavirus
The first case of COVID-19 that was confirmed by a lab test was in a man who started to experience symptoms on December 8, 2019, The Washington Post reported. Although there have been previous reports suggesting that the first case could be traced to December 1 or November 17, such as Previously reported live science, these reports were not confirmed by the WHO-China joint study, said Joel Wertheim, associate professor of medicine at the University of California, San Diego. Wertheim and his colleagues analyzed the genetic information of the virus and performed epidemiological computer simulations, which put the date of origin of the virus between mid-October and mid-November 2019, they reported in April in the journal. Science.
To draw this conclusion, the researchers analyzed the genomes of SARS-CoV-2 from the first wave of the pandemic in China. Because virus accumulating genetic changes over time, researchers could identify a fixed rate of genetic mutation, then work backwards until they find when the first person with a relatively unchanged form of the virus could have started spreading it among people. The researchers estimated that for SARS-CoV-2, this date was between November 17 and December 20, 2019.
But it was just then that the virus probably started to spread among people. Because SARS-CoV-2 native to an animal and was transmitted to humans, the animal coronavirus that originally infected the first person may have genetic differences from the current virus. This version may have been slow to become genetically recognizable as SARS-CoV-2, which means the virus may have started to spread even earlier, the researchers said.
To see how long it took for the virus to accumulate these kinds of changes, the researchers used a computer simulation of the spread of the virus. They concluded that the process would likely have taken anywhere from zero to 41 days, although the most common outcome was eight days. This process, they said, could have pushed back the initial spread of the virus to mid-October.
Wertheim stressed that the aim of the study was to establish how far back the virus is could started to spread, not necessarily at what do propagate. “That’s all you can do, and even then there’s a lot of guesswork going back that far,” he said.
Many researchers, including Pond, would agree that, based on current data, the timeline proposed by Wertheim and his colleagues in the study is likely, said Pond, who co-authored a separate study. examining the early developmental history of SARS-CoV-2, published in May in the journal Molecular biology and evolution. In this study, Pond and his colleagues used a kind of genetic analysis originally developed to reconstruct the evolution of human cancer cells. They determined that the version of SARS-CoV-2 that spread in December 2019 would take six to eight weeks to evolve from the initial human strain of the virus. Although the method used is different, this delay would also push back the origin around the same time as the other study – October 2019.
But Pond said there are also ways to get new information on when the virus first appeared. For example, many believed the virus had emerged from an animal at the Huanan Seafood Wholesale Market in Wuhan, but subsequent analysis revealed cases that could not be linked to the market, Previously reported live science. In contrast, Wertheim said the lack of confirmation from the joint China-WHO study for the Dec. 1 and Nov. 17 cases his study used could affect the estimate. Frozen blood samples from potential early cases or genetic sequence records could also provide additional information, Pond said.
“You can easily imagine a scenario where you get five or 10 more sequences ahead of time, and they change everything,” he said. Either way, Pond believes the virus is unlikely to have emerged before fall 2019 or, at the earliest, late summer 2019, as even the events that could lead to the viruses circulating undetected so early – as they begin to spread, die off and then die back – are very unlikely and become more and more so the further you go.
Some research has suggested an original date prior to October, but the studies have not been peer reviewed or published in scientific journals. In such to study, Harvard University researchers analyzed internet searches in Wuhan, China, from 2019 and found an increase in searches of “diarrhea“in August 2019 which correlated with an increase in traffic in a hospital parking lot in Wuhan the same month. Diarrhea is more common with COVID-19 that with the flu, the researchers therefore suggested that the increase could indicate the spread of the virus in August.
In one remark in response to this study, however, other researchers pointed out that the authors used an awkward Chinese translation for “diarrhea” and that the search term was increasingly used all over China, not just in Wuhan. Another study, which was posted on the preprint server medRxiv and was not peer reviewed, found traces of SARS-CoV-2 in wastewater in Barcelona, Spain, in March 2019. However, the results made little sense without any evidence from patients suffering from symptoms of COVID-19 in Barcelona at the time.
There are inherent problems in trying to find a more precise date of origin. Wertheim’s scans showed that initially the number of cases was likely so low that the virus went undetected. In fact, in computer simulations of the study that modeled the spread of SARS-CoV-2 from a single human case, the virus went extinct most of the time, and when it wasn’t the case, it sometimes relied on one person. to disseminate it again more widely. Of course, in a large, densely populated city like Wuhan, this scenario does not present a problem – it would be easy for one person to transmit the virus to many people. But it is likely that at first few people had the virus. In the midst of a severe influenza season, and since SARS-CoV-2 had a relatively low death rate compared to viruses like Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS), Wertheim said it was no surprise the virus had not been detected. when it started to spread.
Wertheim hopes that systems allowing for earlier detection could help prevent or mitigate the effects of future pandemics.
“In an ideal world, we would have some sort of systematic, interconnected way of reporting any unexpected illness in a way that can be seen across borders,” he said. “Something like that would have given us a head start on this pandemic and potentially could have stopped it in its tracks. “
Originally posted on Live Science.
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