Six Weeks into the 2019 Coronavirus Disease Outbreak: It Is Time to Consider Strategies to Impede the Emergence of New Zoonotic Infections
The emergence of the 2019 coronavirus disease (COVID-19), also known as novel coronavirus pneumonia, has brought global attention to the potential for zoonotic infections to cause widespread epidemics and pandemics. Coronaviruses, which were previously known to cause mild upper respiratory infections in humans, have demonstrated their capacity for severe disease with the outbreaks of severe acute respiratory syndrome (SARS) in 2003 and Middle East respiratory syndrome (MERS) in 2012. The current COVID-19 outbreak, which began in late 2019, underscores the need for strategies to prevent the emergence of new zoonotic infections.
Coronaviruses are a diverse group of viruses that infect a wide range of domesticated and wild mammals and birds. These animals often serve as carriers and reservoirs for coronaviruses. Prior to the COVID-19 outbreak, six coronavirus species were known to cause disease in humans. Four of these species are endemic in human populations and typically cause mild common cold symptoms in immunocompetent individuals. The remaining two species, SARS-CoV and MERS-CoV, are zoonotic in origin and can cause severe, potentially fatal infections in humans. The COVID-19 virus, now designated as 2019-nCoV, is the seventh coronavirus species known to infect humans and is also zoonotic in origin.
Both SARS-CoV and MERS-CoV are believed to have originated from bats, with intermediate hosts playing a crucial role in their transmission to humans. SARS-CoV is thought to have been transmitted to humans via masked civets, while MERS-CoV was transmitted through dromedary camels. Similarly, the genomic sequence of 2019-nCoV is strikingly similar to that of SARS-like coronaviruses found in bats, suggesting that bats are the natural reservoir for 2019-nCoV. It is hypothesized that a coronavirus species in bats crossed the species barrier to an intermediate mammal host, likely a masked civet, which was sold at a wet market in Wuhan, China. Subsequent mutation and transmission to humans initiated the COVID-19 epidemic.
The basic reproductive number (R°) is a key epidemiological metric that indicates the average number of secondary infections generated by a single infected individual. The R° of SARS-CoV was estimated to be around 3, while the R° for 2019-nCoV is currently estimated to be between 2.2 and 2.7. However, a phenomenon known as “super spreading” has been observed in approximately 10% of individuals infected with SARS-CoV and MERS-CoV, where a single individual can spread the virus to more than 10 others. While super spreaders have not yet been identified in the COVID-19 outbreak, clinicians and researchers must remain vigilant for their potential existence and take measures to identify and isolate such individuals to prevent further transmission.
Mathematical modeling studies have provided important insights into the transmission dynamics of 2019-nCoV. Researchers at the University of Hong Kong estimated that the basic reproductive number for 2019-nCoV is 2.68, with a 95% confidence interval of 2.47 to 2.86, and that the epidemic doubling time is 6.4 days, with a 95% confidence interval of 5.8 to 7.1 days. Another study suggested that the basic reproductive number for 2019-nCoV could be as high as 6.47, highlighting the potential for rapid spread of the virus.
The zoonotic origins of 2019-nCoV, as well as those of SARS and MERS, have brought attention to the role of unregulated wet markets in China, where live wild animals are traded for human consumption. These markets increase the potential for viral infections to jump from animal reservoirs to human populations. In response to the COVID-19 outbreak, China implemented a complete ban on the market trading and sale of wild game meat on January 26, 2020. This measure is expected to help prevent zoonotic transmission of 2019-nCoV and reduce the risk of future zoonotic outbreaks.
The economic and human costs of zoonotic outbreaks are substantial. The SARS epidemic in 2003 cost the global economy approximately $54 billion, while the 2015 MERS outbreak in South Korea resulted in a $2.6 billion loss for the country’s tourism industry. The 2014 Ebola outbreak in Guinea, Liberia, and Sierra Leone cost these countries approximately $300 million. The global economic and human costs of the COVID-19 outbreak are expected to be significant, further emphasizing the need for preventive measures.
Efforts to contain the COVID-19 outbreak have been extensive and focused, but much work remains to be done. International cooperation and the implementation of proven public health strategies will be essential for managing the current outbreak. However, it is inevitable that new zoonotic infections will emerge in the future. Therefore, it is imperative for local and international health and wildlife regulatory authorities to establish and enforce robust control mechanisms to reduce human exposure to wild game meat and their products.
In Asia, the consumption of wild game meat is often motivated by beliefs in its medicinal value and health-enhancing effects, as well as its use as a status symbol. The existence of local and international wildlife trade for meat and animal products needs urgent and decisive change. It is hoped that the efforts by China, in partnership with the international community, will yield positive results in controlling the COVID-19 outbreak. Additionally, urgent attention to and curtailment of the unregulated trade in wild game, meat, and products are essential to prevent future zoonotic outbreaks and the associated human and economic losses.
In conclusion, the COVID-19 outbreak has highlighted the ongoing threat of zoonotic infections and the need for comprehensive strategies to prevent their emergence. By addressing the root causes of zoonotic transmission, such as the trade and consumption of wild game, and by implementing effective public health measures, it is possible to reduce the risk of future outbreaks and protect global health and economic stability.
doi.org/10.1097/CM9.0000000000000760
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