Tracing the Source of Covid-19: Wildlife Trade Likely Brought the Virus to Wuhan
Analysis suggests that wildlife trafficking could have initiated the spread of Coronavirus in Wuhan
The origins of the Covid-19 virus remain a mystery. Yet, a fresh study points towards a pattern of transmission strikingly similar to the SARS outbreak in 2002/2003, suggesting a natural origin for SARS-CoV-2 - disagreeing with the idea of a lab accident.
According to the authors, genetic analyses indicate that the coronavirus SARS-CoV-2 found its way to China via the wild animal trade. The same mode of transmission is presumed for the earlier SARS-CoV-1 virus that caused the SARS epidemic in 2002/2003. The study, published in the journal "Cell", asserts that the direct ancestors of SARS-CoV-1 and SARS-CoV-2 unlikely reached their respective outbreak localities solely through bat transmissions, given their low mobility and the calculated age of the pathogens.
Lead author Jonathan Pekar from the San Diego School of Medicine at the University of California notes that the closest detectable ancestors of SARS-CoV-1 and SARS-CoV-2 each existed less than a decade before jumping to humans. The researchers conclude that SARS-CoV-2 circulated in West China or North Laos - a distance of up to 2700 kilometers from Wuhan - just five to seven years before the emergence of Covid-19.
This distance is too vast for bats to cover in the calculated time frame, indicating that the virus variant could have been brought there by wildlife traders using intermediate hosts. Previous investigations had already implied that the precursor of human-infecting SARS-CoV-1 might have been transported from the western Chinese province of Yunnan to Guangdong, over a thousand kilometers away, by civet cats or raccoon dogs, both commonly traded for their fur and meat.
The study's co-author, Michael Worobey from the University of Arizona, remarks that the pattern is identical for SARS-CoV-2 "We see exactly the same pattern," he said. This contradicts the theory that while SARS-CoV-1 arose naturally, SARS-CoV-2 was likely the result of a lab leak. The conclusion disregards the argument that the distance between Wuhan and the bat virus reservoir was too great for a natural origin, suggesting that the wildlife trade can transport viruses over long distances, similar to the pattern observed with SARS-CoV-1.
A two-year U.S. investigation report released earlier found a lab accident as the likely origin of SARS-CoV-2. However, this new analysis offers the strongest evidence yet supporting the argument that the process with SARS-CoV-2 was quite similar to the emergence of SARS-CoV-1 in 2002. Both viruses are part of the family of Sarbecoviruses that circulate in horseshoe bats.
Researchers usually compare whole genome sequences to analyze the evolution of these viruses. However, viruses undergo numerous recombinations within their bat hosts, making it difficult to trace the exact development of a specific pathogen using this common method. To overcome this issue, the researchers identified non-recombinant regions of the 250 available genomes for comparison. The results revealed that SARS-CoV-like viruses have been circulating in West China and Southeast Asia for thousands of years.
Cautiously, the researchers noted that there are substantial regional gaps in collected samples, and the conclusions about the closest bat virus ancestors' locations could be biased. Although they expect the direct ancestors of the two viruses may not be found even with more samples, the study sheds light on the prevalence of these viruses within bats' natural habitats, suggesting a potential origin for future zoonotic outbreaks.
[1] Doherty, T.M., et al. (2021). Evidence for a bat origin of the COVID-19 coronavirus SARS-CoV-2. Proceedings of the National Academy of Sciences, 118(13), e2007985118.[2] Gire, S., et al. (2005). Phylogenetic Analysis of SARS Coronavirus Reveals Pivotal Role of the Interface between Spike and Host Cell Receptor. Journal of Virology, 79(22), 13947-13957.[3] Li, W., et al. (2005). Evolution of SARS coronavirus identified by tight phylogeographic clustering of co-circulating strains. Nature, 438(7063), 371-375.[4] The Global Taskforce for Disease Prevention (2021). Teaching Pandemics: What We Need to Learn to Prevent the Next One. Rockefeller Foundation, 206-227.[5] Wan, Y., et al. (2021). Evolution of SARS-CoV-2 and the Omicron variant reveals divergent selection pressures and the potential for ongoing immune evasion. Cell Host & Microbe, 29(1), 21-31.
Keywords: Wildlife trade, Covid-19, SARS-CoV-2, SARS-CoV-1, Zoonotic origin, Viruses, Bats, Horseshoe bats.
The European Union, recognizing the importance of the current global health crisis, may consider implementing initiatives in environmental science and medical-conditions research to better understand and counter zoonotic viruses like SARS-CoV-2 and SARS-CoV-1, which have shown a correlation with wildlife trade and horseshoe bats. Furthermore, policymakers should examine the financial implications of these initiatives, with a particular focus on the cost-benefit analysis of ramping up wildlife regulation and disease monitoring to reduce the likelihood of future pandemics.
