世卫组织新冠病毒溯源联合研究报告（英）-世卫组织-2021.2-120页_3mb

Summary of WHO-convened Global Study of Origins of SARS-CoV-2: China Part

Core Content

The WHO-convened Global Study of Origins of SARS-CoV-2: China Part was conducted from 14 January to 10 February 2021 as part of the One Health approach to understand the zoonotic source and introduction route of the virus into the human population. The study aimed to prevent future zoonotic outbreaks and reduce the risk of transmission from animals to humans.

Main Findings

Epidemiology

• Surveillance data from late 2019 and early 2020 showed no evidence of SARS-CoV-2 affecting morbidity in Wuhan prior to the outbreak.
• All-cause mortality and pneumonia-specific mortality in Wuhan and Hubei Province increased rapidly in late 2019 and early 2020, indicating widespread transmission by January 2020.
• National Notifiable Disease Reporting System (NNDRS) reported 174 cases with symptom onset in December 2019, but none were confirmed as SARS-CoV-2 after further testing and review.
• Many early cases were linked to the Huanan Seafood Wholesale Market, but others were not, suggesting that the market may not have been the original source of the outbreak.

Molecular Epidemiology and Bioinformatics

• The genomic data of SARS-CoV-2 showed high homology with RaTG13, a coronavirus found in horseshoe bats, and to a lesser extent with pangolins.
• Bats and pangolins are considered potential reservoirs for SARS-CoV-2, but no direct progenitor has been identified.
• Mink and cats are highly susceptible to SARS-CoV-2, indicating that additional animal species could serve as reservoirs.
• The time to most recent common ancestor (tMRCA) of SARS-CoV-2 was estimated to be between late September and early December 2019, suggesting the outbreak may have started before the first confirmed cases in Wuhan.

Animal and Environment Studies

• Over 80,000 samples from wildlife, livestock, and poultry across 31 provinces in China were tested, but no positive results for SARS-CoV-2 were found.
• Environmental sampling at the Huanan market revealed 73 positive samples out of 923, indicating widespread surface contamination.
• Cold-chain products from 20 countries were found to have SARS-CoV-2 sequences or close relatives, suggesting potential pathways for virus introduction.
• Frozen food and packaging can carry SARS-CoV-2 over long distances, and further studies are needed to trace these products back to the Huanan market.

Possible Pathways of Emergence

The study evaluated four possible pathways for the emergence of SARS-CoV-2:

1. Direct zoonotic transmission – Considered possible-to-likely.
2. Introduction through an intermediate host – Considered likely to very likely.
3. Introduction through the cold/food chain – Considered possible.
4. Introduction through a laboratory incident – Considered extremely unlikely.

Key Recommendations

• Conduct further studies on trade and history of animal and product trade in other markets, especially those epidemiologically linked to early human cases.
• Perform surveys on susceptible animals in South-East Asia and other regions to identify potential reservoirs of SARS-CoV-2-related viruses.
• Trace frozen products back to the Huanan market and investigate their role in virus transmission.
• Serologically test farmers, suppliers, and workers with occupational exposure to animals and cold-chain products for unusually high antibody titres.
• Convene a global expert group to support future traceability research on the origin of epidemics.

Conclusion

The study concluded that while direct zoonotic transmission and intermediate host involvement are the most likely pathways, further research is needed to confirm these hypotheses. Cold-chain products and further animal surveys are also recommended to explore alternative transmission routes and prevent future outbreaks.

Key Contributors

• WHO and Chinese experts worked together on epidemiology, animal and environment, and molecular epidemiology.
• International experts from 17 countries were involved, including GOARN and OIE.
• Key individuals included Prof. Huang Fei, Prof. Liu Jiangmei, and Dr. Wu Yang, among others.

References

• Huang CL et al. (2020). Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet.
• Nishiura H et al. (2020). Initial cluster of novel coronavirus (2019-nCoV) infections in Wuhan, China. J Clin. Med.
• Hu B et al. (2017). Discovery of a rich gene pool of bat SARS-related coronaviruses. PLoS Pathog.
• Latinne A et al. (2020). Origin and cross-species transmission of bat coronaviruses in China. Nature Communications.
• Zhu N et al. (2020). A novel coronavirus from patients with pneumonia in China. New England Jjournal of Medicine.
• Wu F et al. (2020). A new coronavirus associated with human respiratory disease in China. Nature.
• Chan JF et al. (2020). A familial cluster of pneumonia associated with the 2019 novel coronavirus. Lancet.
• Petersen E et al. (2020). Comparing SARS-CoV-2 with SARS-CoV and influenza pandemics. Lancet Infect Dis.

Summary and Recommendations

• The Huanan market may not have been the original source of the outbreak, but its role in transmission remains unclear.
• Bats and pangolins are potential reservoirs, but no direct progenitor has been confirmed.
• Cold-chain products and further animal testing are needed to explore alternative transmission routes.
• Global collaboration is essential for traceability and preventing future zoonotic events.

This study provided valuable insights into the origins and transmission of SARS-CoV-2 and highlighted the need for continued research and international cooperation to enhance preparedness for future outbreaks.