Reporters : Han Yadong, Jing Peixuan, Sun Jiawei
Editor : Ding Baoxiu
Publisher : Central Commission for Discipline Inspection, National Supervision and Administration Commission website, re-produced on China News Network
Translation, editing : Gan Yung Chyan
/ KUCINTA SETIA
Image : Video Screenshot
At 8 p.m. on 17 June 2020, a minibus entered the southern part of the viral disease research centre of the China CDC at 100 Yingxin Street, Xicheng District, Beijing. Wu Guizhen, chief expert in biosecurity at the China CDC the Party Committee of the Viral Disease Institute, led a team of people in a hurry to the minibus and rushed to the Xinfadi agricultural product wholesale market, where the epidemic outbreak broke out. This is the third time that a viral disease research centre staff have entered Xinfadi to carry out coronavirus tracing.
On 11 June, after 57 consecutive days of no new confirmed cases in Beijing, local cases reappeared. Where did the sudden SARS-CoV-2 come from? What have been discovered by China CDC in Xinfadi? What are the latest developments in coronavirus tracing? The reporters from the website of the Central Commission for Discipline Inspection of the National Commission for Discipline Inspection interviewed experts on viral diseases.
Nuclear nucleic acid positive specimens were detected in the Xinfadi agricultural products wholesale market
On 14, 15 and 17 June 2020, experts of the Viral Disease Institute entered the new agricultural product wholesale market three times in succession.
It is understood that during the first time, experts from the virus research centre collected a total of more than 200 samples, among which many new coronavirus nucleic acid positive samples are detected. The second time, they followed the vines and collected more than 200 samples in other areas, many of which are positive. For the third time, they are scientifically testing samples collected from water systems on the market, fish farming preservation water, aqueducts, groundwater and other water bodies. At the same time, air samples have been collected to determine the risk of aerosol transmission. The samples are currently being tested.
Why can we collect so many positive samples in a short time? What does this mean?
Liu Jun said, "Many of us have participated in traceability work in Wuhan before, and we still have some experience."
As a team leader in Wuhan, the researcher Liu Jun, Assistant Director of the Institute of Viral Diseases and Deputy Director of the National Influenza Center, explained, "How did the coronavirus come about? There are some speculations: Contaminated seafood or meat products are transported to the market through the cold chain logistics to cause transmission, or infected people enter the market to cause transmission. For these two possible sources, we speculate that some environmental locations as well as items, food etc may have been contaminated by the virus."
Liu Jun added, "For example, we first tested frozen products such as fish and shrimp, as well as cutting boards, counters, and chopping boards that may be exposed to these frozen products in large quantities. The possibility of their contamination by viruses is very high. In addition, we also thought that after detoxification in the market, people infected with SARS-CoV-2 may contaminate the environment. For example, will the droplets from sneezing hit the wall or the surface of the refrigerator? Will the ground, the surrounding fish tanks, water ditches, etc. be polluted? These are the samples we have to focus on."
"On the other hand, the fact that we have detected so many positive samples also shows that the entire environment is contaminated with viruses." Researcher Wu Guizhen said. He revealed that when they first entered the new development site, they were detected at a seafood store on the ground floor. Some positive samples were included, including a whole salmon oral swab, and the adjacent ditch; the second time, positive samples were also collected two kilometres away from the aquatic market.
Liu Jun commented, "In the virus tracing work, sampling and testing of environmental samples including fish and shrimp shells, fish farming water, frozen products in the refrigerator and so on is very important. Different positive samples point to different conclusions: it may point to the environment and the animals or objects inside it are the source of infection, or it may point to the person infected by the novel coronavirus as the source of infection. For example, positive samples were found on the sealed frozen products, which further confirmed the possibility of virus transmission to the market through the cold chain logistics; and if the frozen products have been opened, this indicates that these frozen products may have been contacted by people before. Then the conclusions drawn are not the same."
On 18 June 2020, China CDC has completed and released the whole disease genome sequencing of dozens of positive specimens after intense and orderly work in the virus research centre, a P3 laboratory. There are three main types. Please click this news link for detailed information: https://staygate.blogspot.com/2020/06/china-cdc-publishes-xinfadi-viral.html
Seasonal closure of the seafood market can easily lead to the rapid spread of the coronavirus
Since the occurrence of the new epidemic, the official cumulative number of confirmed cases in Beijing has exceeded 100, reaching 158. Why is the epidemic outbreak concentrated on the wholesale market and a large number of cases occur in a short period of time?
As the leader of the coronavirus tracing team that went to Wuhan to carry out virus tracing work, Liu Jun had entered the Wuhan Huanan Seafood Market 20 times, and this time entered the agricultural product wholesale market in Xinfadi three times.
"I have been in both markets, because it is the seafood market, we can see that their environment is relatively cold. Microorganisms including viruses are afraid of heat or cold, and can survive for a long time in such an environment. And here is not only wet and cold They are still closed and have poor ventilation, which can also contribute to the spread of the virus. For example, if a person infected with SARS-CoV-2 sneezes, it is difficult to spread out, and the droplets may settle to the ground. After sweeping the ground, they pollute other places." Liu Jun said.
"So the ventilated and dry environment is not conducive to the spread of the virus, and the wet and cold environment is relatively easy to cause the rapid spread of the coronavirus." Liu Jun concluded.
Seasonal closure of the seafood market is conducive to the survival and spread of the virus, which helps explain why there are a large number of cases here in a short period of time. However, this does not mean that the seafood market itself is the source of the coronavirus.
"Where is the source of the virus and why the outbreak is concentrated in the seafood market? These are two different levels of problems. We cannot conclude that the virus must have originated here because of the concentrated outbreak of the virus in the seafood market." Liu Jun said.
Wu Guizhen said, "In the past, we have been looking for intermediate hosts when doing virus tracing. Now it may be time to re-examine whether the virus comes from wild animals. This epidemic rebounded in Beijing, and it was also a concentrated outbreak in the wholesale market. However, unlike the Huanan Seafood Market in Wuhan, the possibility of wild animals causing an epidemic in Beijing is very small. This leaves us with an important tip: Is it possible that the source is an infected person or contaminated food, and the seafood market? The environment has created an opportunity for rapid spread."
Liu Jun also believes that the coronavirus at Xinfadi may be caused by the transmission of contaminated seafood or meat products to the market through cold chain transportation, or it may be caused by the infected people entering the market. "There are different possibilities, but the possibility of the outbreak from wild animals is very small."
The newly detected SARS-CoV-2 strain is older than the strain currently circulating in Europe
On 16 June, Gao Fu, Director of the China CDC, speculated in a public speech: "SARS-CoV-2 will lurch in some dark and humid, relatively polluted, and bad environment, which is not what everyone thought. In the future, it will be suddenly exposed to many people within a certain period of time. This time, in Beijing the first patient may not appear in early June and the end of May. It is likely to be pushed a month in advance. There are already many asymptomatic infections or light patients in this area so that there can be so many coronaviruses in the environment."
"A large range of positive specimens have been detected in the environment of the Xinfadi agricultural wholesale market, and it does give us some hints: this virus has been in for a while. If it is said that it is only a short time, there may not be such a large pollution. This is the focus. Of course, this also needs more data to confirm." Zhang Yong, Assistant Director of the Viral Disease Institute, said.
Determining the time of virus epidemic, the main method currently adopted is genomic epidemiology. "First of all, the whole genome of the virus is sequenced. After sequencing, the different viruses are put together using bioinformatics analysis methods to see which virus has more mutations. The more changes are generally the viruses that have been updated after evolution, with fewer mutations. If it is closer to the original virus, it will be prevalent earlier, and it will be older. Of course, these are popular sayings. In addition, there are some specific algorithms that are calculated through mathematical models." Liu Jun introduced.
From the preliminary results of genomic epidemiology, this coronavirus strain came from Europe, but it is different from the coronavirus strain that is currently circulating in Europe. It is older than the strain that is currently circulating in Europe.
Zhang Yong analyzed how the coronavirus entered Xinfadi, "There are several possibilities involved. For example, the coronavirus is lurking in the imported frozen food. During the entire storage and transportation period from overseas to the territory, the virus has not evolved because it has been frozen, so no mutation has occurred; it is also possible that the virus is lurking in a dark and humid environment such as Xinfadi agricultural wholesale market, without being disinfected or sterilized, and suddenly exposed to infected people within a certain period of time, resulting in slower evolution. The result is that these strains are closer to the old European viruses."
Although the virus transmission path still needs more evidence to confirm or falsify, this preliminary speculation derived from genomic epidemiology may be able to uncover a new place for the comprehensive use of epidemiological investigations and big data technology. The mystery of the source of the coronavirus provides useful ideas.
Zhang Yong said, "Rheology and big data may find the connection between cases, but sometimes it is impossible to determine who infected them. Through laboratory testing and gene sequence analysis, we can know the transmission path between them. When we speculate about the possible transmission relationship between viruses, we can further find corresponding evidence through methods such as flow regulation. With the funding of the National Science and Technology Major Project, the Viral Disease Institute is leading the preparation of a nationwide virus-based genome. Virus network monitoring and tracing technology system to deal with the major problem of virus tracing relate to national security prevention and control of viral diseases."
How is an old coronavirus circulating in Europe brought to Beijing's Xinfadi agricultural wholesale market? Scientists continue to explore day and night.
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