Nature: WHO mentioned still five unsolved mysteries for COVID-19
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Nature: WHO mentioned still five unsolved mysteries for COVID-19
Nature: WHO mentioned still five unsolved mysteries for COVID-19. Where does COVID-19 come from? The investigators of the World Health Organization told the journal Nature about their investigation progress and questions to be answered.
After conducting a one-month tracing investigation of the source of the COVID-19 pneumonia in China, the World Health Organization’s investigation team concluded that the virus may have originated in bats and spread to humans through intermediaries. But where does the new coronavirus come from? There are still five unsolved mysteries.
Has the new coronavirus spread in Wuhan before the first confirmed case was discovered?
Confirmation of “Patient Zero” is vital to the traceability of the virus. Peter Ben Embarek, a WHO food safety scientist in Geneva and a member of the investigation team, said that it has been clear that the first person to be diagnosed with the COVID-19 virus is an office worker in Wuhan who has no recent travel history and began to show symptoms on December 8, 2019. But the virus may have spread in the city before he was infected, because the COVID-19 virus began to break out in Wuhan on a large scale in late December.
The previous evidence also confirmed this. Chinese researchers conducted an extensive survey of patients who attended various hospitals in Wuhan from October to December 2019. Fewer than 100 patients had symptoms of COVID-19 pneumonia. Subsequently, the blood of these 67 people was tested, and no antibodies produced after the new coronavirus infection were found in their bodies. This shows that there were no large-scale cluster infections in Hubei before December, and there were no abnormal peaks of deaths around Hubei Province.
But Peter Ben Embarek said that the analysis should be repeated using less restrictive symptom criteria to ensure that researchers find all potential cases of COVID-19 pneumonia.
Dominic Dwyer, a member of the research team, director of pathology at the Department of Health of New South Wales, Australia, and medical virologist, said that Chinese scientists should also look for evidence of past infections in about 200,000 blood samples kept in Wuhan Blood Center and other parts of China , Further confirming that the virus had spread among the population before December 2019, and not only in the population who went to medical institutions at that time.
Some scientists who did not participate in the World Health Organization investigation studied blood samples collected in Guangzhou, China a year before the outbreak, and found that some samples were positive for antibodies to the new coronavirus (close relatives of the new coronavirus were found in bats and pangolins in southern China). But Ian Lipkin, an infectious disease researcher at Columbia University in New York City who is engaged in analytical work, said that the test is not enough to prove that these antibodies are not caused by other viral infections, and there are still many experiments that have not been completed.
Did the new coronavirus spread to people outside of China before December 2019?
Previously, European researchers reported that antibodies to the new coronavirus were found in European blood bank samples collected in November 2019.
Ben Embarek said that this does not indicate that the virus originated in Europe, but it can prove that the virus had spread in Wuhan before the first case in Wuhan appeared. “At the time, Wuhan was an international city with very convenient transportation. There were direct flights to all parts of the world every day. If the virus spreads in Wuhan, it would be easy to take passengers to other parts of the world and then spread again in different regions.”
In addition, he suggested retesting blood samples in Europe to confirm whether it is a COVID-19 case.
What “role” did the South China market play in the spread of the epidemic?
The “intermediate animal” that passed the new coronavirus from bats to humans has not yet been determined, but researchers believe that it may be some kind of wild animal sold in the fresh market in the form of food. In the early stage of the outbreak, investigators turned their attention to the South China Seafood Market in Wuhan because it sold fresh and frozen animals and many early infected people had been there. However, other early cases unrelated to the South China Seafood Market were also found later, and this view was questioned. Although the virus was found in sewers and sewage in the market, no new coronavirus was found on animal carcasses.
Nevertheless, the South China Seafood Market was the only place where a large number of infected people came into contact with meat and animals at the beginning of the outbreak. Hung Nguyen-Viet, a WHO member and environmental and food safety researcher, said it is important to determine how the new coronavirus enters the market and whether it is present in animals.
The research team identified ten stalls selling wild or farmed animals that may bring the virus to the market from farms in southern China. Some wild animals, such as rabbits and ferrets, are easily infected with the new coronavirus or related viruses that cause severe acute respiratory syndrome (SARS).
Peter Daszak, a member of the WHO team, believes that these farms should be investigated to confirm whether there are infections in animals or workers. He also wants to know which animals are on sale in other markets in Wuhan. Daszak said that the first confirmed infected person mentioned in an interview with the team that his parents had been to the fresh market in the local community.
Did frozen wild animal meat play a role in early transmission?
The WHO investigation team concluded that the virus was probably transmitted to humans through live animals, but Ben Embarekr believes that the virus may enter the South China market through frozen wild animals infecting farms, and then caused an epidemic. Daszak doubts whether the frozen ferrets sold in the market may carry the virus. He said: “It may be on the skinned animal carcasses, not the meat in a plastic bag.”
Although Chinese researchers isolated viral RNA from the packaging of imported frozen fish, Ben Embarek said that the WHO investigation team concluded that these products are unlikely to be the first route for the new coronavirus to enter Wuhan.
Lipkin said that there is no evidence that the new coronavirus entered the market through infected frozen wild animals, and infected people who have been in contact with wild animals can easily spread the virus.
Before the outbreak, did the new coronavirus spread among animals in China?
In order to determine the animals that transmit the virus to humans, researchers need to find evidence of the new coronavirus in the species. Chinese researchers tested 30,000 animals in 2019 and 2020. These 30,000 animals include wild, farmed and domestic animals. Except for the virus found in some cats in Wuhan in March 2020, there is no evidence that other animals have live viruses or have been infected with the new coronavirus.
But Ben Embarek said that these investigations cannot represent the overall situation of Chinese animals, and more animals need to be tested for infection, especially animals in wild animal farms. Daszak said: “The number of tests that have been conducted is not enough to show that the wild animal farms are not carrying the new coronavirus.”
Daszak believes that the rapid outbreak in Wuhan in December 2009 indicated that the virus was most likely introduced through a wildlife trade. He said that future testing should focus on farmed wild animals.
(source:internet, reference only)
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