Future coronavirus outbreaks are highly likely to originate in China from bats, experts had warned in 2019
Scientists from China had warned in 2019 that it is highly likely that future coronavirus outbreaks — such as the Severe Acute Respiratory Syndrome (SARS) and the Middle East Respiratory Syndrome (MERS) — will originate from bats and that there is an increased probability that it will occur in China.
Many experts believe that the COVID-19 virus was passed from bats to a mystery animal species that then passed it on to people.
"It is generally believed that bat-borne coronaviruses will re-emerge to cause the next disease outbreak. In this regard, China is a likely hotspot. The challenge is to predict when and where so that we can try our best to prevent such outbreaks," said the research team from CAS Key Laboratory of Special Pathogens and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan; and the University of Chinese Academy of Sciences, Beijing.
Based on their review, four experts from China had cautioned that the investigation of bat coronaviruses becomes an urgent issue for the detection of early warning signs, which, in turn, minimizes the impact of such future outbreaks in China.
The review — titled 'Bat Coronaviruses in China' — was published in the journal Viruses on March 2, 2019. It is a monthly peer-reviewed open access scientific journal of virology published by MDPI. According to available information, the paper was received on January 29, 2019, revised on February 26, 2019, and accepted February 26, 2019, for publication.
For the review, the team collected information from past epidemiology studies on bat coronaviruses in China, including the virus species identified, their host species and their geographical distributions. They also discussed the future prospects of bat coronaviruses cross-species transmission and spread in China.
Why bats?
According to experts, bats are the only mammals with the capability of powered flight, which enables them to have a longer range of migration compared to land mammals. Bats are also the second-largest order of mammals, accounting for about a fifth of all mammalian species, and are distributed worldwide.
"It is hypothesized that flight provided the selection pressure for coexistence with viruses, while the migratory ability of bats has particular relevance in the context of disease transmission. Indeed, bats were linked to a few highly pathogenic human diseases, supporting this hypothesis," said the study.
It added, "Some of these well-characterized bat viruses, including bat lyssaviruses (Rabies virus), henipaviruses (Nipah virus and Hendra virus), coronaviruses or CoVs (SARS-CoV, MERS-CoV, and swine acute diarrhea syndrome coronavirus or SADS-CoV), and filoviruses (Marburg virus, Ebola virus, and Mengla virus), pose a great threat to human health."
The researchers further explained that a comprehensive analysis of mammalian host-virus relationships shows that bats harbor a significantly higher proportion of zoonotic viruses than other mammalian orders. Viruses from most of the viral families can be found in bats. "Bats are now recognized as important reservoir hosts of coronaviruses," they added.
Why China?
Experts say China is the third-largest territory and is also the most populous nation in the world. "A vast homeland plus diverse climates bring about great biodiversity including that of bats and bat-borne viruses — most of the International Committee of Taxonomy of Viruses (ICTV) coronavirus species were named by Chinese scientists studying local bats or other mammals. The majority of the CoVs can be found in China," said the team.
Researchers explain that most of the bat hosts of these coronaviruses live near humans, potentially transmitting viruses to humans and livestock. Chinese food culture maintains that live slaughtered animals are more nutritious, and this belief may "enhance viral transmission".
The researchers further said two bat coronaviruses caused outbreaks in China and it is thus urgent to study the reasons to avoid future outbreaks.
During the past two decades, three zoonotic coronaviruses have been identified as the cause of large-scale disease outbreaks – SARS, MERS, and SADS. SARS and MERS emerged in 2003 and 2012, respectively, and caused a worldwide pandemic that claimed thousands of human lives, while SADS struck the swine industry in 2017.
They have common characteristics, such as they are all highly pathogenic to humans or livestock, their agents originated from bats, and two of them originated in China.
"15 years after the first highly pathogenic human coronavirus caused the SARS coronavirus (SARS-CoV) outbreak, another SADS-CoV devastated livestock production by causing fatal diseases in pigs," said experts.
They added, "Both outbreaks began in China and were caused by coronaviruses of bat origin. This increased the urgency to study bat coronaviruses in China to understand their potential of causing another virus outbreak."
Prediction model
To predict the next coronavirus that will cause a virus outbreak in the future, the team listed the general factors that may contribute to this outbreak.
"Firstly, bats host a large number of highly diverse CoVs. It is known that CoV genomes regularly undergo recombination during infection, and a rich gene pool can facilitate this process. Secondly, bat species are widely distributed and live close to humans. Thirdly, the viruses are pathogenic and transmissible."
"In this context, SADS-CoV and SARS-CoV outbreaks in China are not unexpected. By this model, there are other CoVs that have not yet caused virus outbreaks but should be monitored," said the analysis.
Researchers said that admittedly, the analysis may be affected by inaccurate or incomplete data. For example, not all research groups performed bat species identification or used Global Positioning System (GPS) during bat sampling, they explain. Bats in the north or west provinces were not surveyed either. "Nonetheless, we believe this analysis is a good starting point for further research," the team emphasized.
Experts said it is critical to answer a few questions — why there are so many genetically divergent CoVs in bats, the exact transmission routes of SARS-CoV and SADS-CoV from bats to humans or swine, and how can bats maintain coronaviruses long-term without showing clinical symptoms of diseases.
"The pathogenesis of most bat coronaviruses in humans remains unknown as the viruses have never been isolated or rescued -- apart from the viruses identified during the outbreaks, many viruses pose a threat to human health. While we start to unveil the mystery of unique bat immunity, there is still a long way to go before we can fully understand the relationship between bats and coronaviruses," they cautioned.