Xinhua News Agency, Beijing, March 30 A joint study on novel coronavirus traceability between China and the World Health Organization (WHO) was officially released in Geneva on July 30. According to the report, it is “highly unlikely” that novel coronavirus has passed from laboratory to human, and “relatively to very likely” that it has been introduced to humans via an intermediate host.
There are four approaches and five levels
On January 14 of this year, 17 Chinese and 17 foreign experts formed a joint expert group, divided into epidemiology, molecular traceability, animal and environment three working groups. They carried out a 28-day global traceability research in Wuhan, China, and wrote a research report on the basis of this.
Based on the existing scientific evidence and findings, the panel assessed the qualitative risk of the possible introduction of novel coronavirus into four transmission routes in humans, and rated it on five levels of “highly unlikely”, “unlikely”, “likely”, “relatively likely” and “very likely”.
According to the report, novel coronavirus is “likely to very likely” to have passed directly to humans from primitive animal hosts, “likely to very likely” to have been introduced to humans via intermediate hosts, “likely” to have passed to humans through cold-chain food, and “highly unlikely” to have passed to humans through laboratory events.
The original source remains a mystery
To detect and confirm early cases of COVID-19, the epidemiology working group evaluated surveillance data on respiratory disease incidence in Wuhan and surrounding areas at the end of 2019. None of these studies showed that novel coronavirus affected the incidence of respiratory disease in the months before the COVID-19 outbreak.
According to the evaluation of more than 76,000 respiratory disease case records from 233 medical institutions in Wuhan in the two months before the outbreak of COVID-19, none of these cases were caused by novel coronavirus infection, so it is unlikely that “substantial transmission” of novel coronavirus will occur in Wuhan during October to November 2019.
The study also found that many of the early cases were linked to the Wuhan South China Seafood Market, but many were linked to other markets and some early cases were not linked to any market at all. In December 2019, transmission of the virus within the wider community could lead to cases not associated with the South China seafood market. This evidence may indicate that the South China seafood market was not the original source of the outbreak.
Potential early transmission in other countries
The Molecular Traceability Working Group analysed genomic data on viruses collected from animals. It has been shown that the coronavirus closest to novel coronavirus exists in bats and pangolins, suggesting that these two mammals may be the host of novel coronavirus, but the virus similarity is not enough to make it a direct ancestor of novel coronavirus. In addition, animals such as minks and cats are highly susceptible to novel coronavirus, suggesting that other animals may be potential hosts.
The working group also conducted an in-depth analysis of sequence data from virus samples collected between December 2019 and January 2020 to understand the diversity of virus sequences during the first phase of the outbreak. Several samples from patients with a history of exposure to seafood markets in South China had the same viral genome sequence, suggesting that the patients came from the same cluster of infections. However, the data also showed that there was already a diversity of virus sequences in the early days of the outbreak in Wuhan, indicating the existence of an unsampled chain of transmission outside the South China seafood market.
The Working Group also evaluated data from published studies in different countries showing that the spread of novel coronavirus generally precedes the initial detection of cases there by several weeks. Suspected positive samples in other countries were found even before the first case in Wuhan, suggesting the possibility of undetected transmission in other countries. Investigating these potential early coronavirus transmission events “is important,” the report concluded.
The relationship with the cold chain is unclear
In the sampling and testing of Chinese wild animals, the Working Group on Animals and Environment did not find the presence of novel coronavirus. The Working Group on Animals and the Environment has analysed coronaviruses related to novel coronavirus found in animals such as Chrysanthemum bats and pangolins. No novel coronavirus antibody or nucleic acid positive results were detected in more than 80,000 samples of wild animals, domestic animals and poultry collected from 31 provinces, autonomous regions and municipalities in China before and after the outbreak.
By the time the South China seafood market was closed, 73 out of 923 environmental samples from the market had tested positive for coronavirus, indicating widespread environmental contamination of the virus, consistent with the conclusion that novel coronavirus could spread to humans through contaminated products.
Novel Coronavirus has been found in frozen foods, packaged products, and cold chain products. Some recent outbreaks in China have been linked to the cold chain, and Novel Coronavirus has been found on parcels and products exported to China from some other countries, indicating that viruses can be carried over long distances through the cold chain. The supply chain in the South China seafood market includes cold-chain products and animal products from 20 countries, some of which tested positive for the novel coronavirus in samples taken before the end of 2019, and some of which have a close relative of the novel coronavirus. Although there is evidence that some commercially marketed animals are susceptible to novel coronavirus, none of the animal products sampled from the market for this study tested positive for novel coronavirus.
Report put forward further research Suggestions joint panel, including the establishment of global unified database, in the broader global continue to look for possible early cases, by the global scientists are looking for could be many more virus host animal species, to learn more about cold chain and frozen food role in the spread of the virus process, etc.