The Creatures Behind the Coronavirus Outbreak.
Research finds that the 2019 outbreak of coronavirus may be a combination of different strains found in bats and snakes. Whilst this may speed up the development of treatments in the future, scientists warn that disrupting bat habitats may potentially increase the spread of similar deadly diseases.
On December 31st, the first cases of severe pneumonia in the Chinese city of Wuhan were reported to the World Health Organization. On January 7th, the cause of these illnesses was identified as a novel strain of the coronavirus. On January 11th, authorities confirmed that the virus had claimed its first life.
Nearly two months later, the mysterious coronavirus, now called 2019-nCoV or COVID-19, has spread to 29 countries and taken the lives of 2,012 people with a fatality rate exceeding 12%. According to the latest figures, there have been more than 75,000 confirmed cases with approximately 60,000 people currently infected with the virus; however, due to the nature of this virus' incubation being between two days and two weeks, this number is considered to be inaccurate and expected to rise dramatically over the next few weeks.
Unfortunately, potential treatments against the virus are still months away from human testing and a vaccination is unlikely to be successfully developed for several years; however, academic research is beginning to shed light on the origin of the coronavirus outbreak. A recent study from researchers at Peking University in Beijing claims that the virus is a combination of different coronavirus strains found in bats and snakes.
By conducting an in-depth genetic analysis of this particular strain and comparing it to various local geographic locations and multiple potential host species, the scientists have determined that the virus may have originated in bats and then resided in snakes before being transmitted to humans.
According to Wei Ji, author of the paper in the Journal of Medical Virology, "Results derived from our evolutionary analysis suggest for the first time that snake is the most probable wildlife animal reservoir for the 2019-nCoV."
This finding has been somewhat supported by the discovery that the first patients infected with the 2019-nCoV had visited the same market in Wuhan where seafood, farm animals, poultry, bats and snakes were sold.
Despite this study being a significant step forward in understanding the genetic composition and evolution of this virus, it is the inclusion of bats within the origination of 2019-nCov that has many scientists concerned.
This is because bats are known carriers of other deadly diseases: they were considered to be the originating host animal of severe acute respiratory syndrome (SARS) which claimed the lives of 774 people in 2003 as well as the Ebola, Marburg, Nipah and Hendra viruses.
A new study from the University of California, Berkeley, has investigated why bats may be involved in so many outbreaks of deadly viruses and found some fascinating, yet worrying, results.
By modelling bat immune systems on a computer, the researchers were able to test how different cells responded to viral infections. They found that when bats are infected, cells quickly release a type of signalling protein called interferons that cause other cells to wall themselves off.
This may support the bats' own immunological defence against viral infections; it also encourages the virus itself to reproduce faster when inside a host, which in-turn makes the virus significantly more dangerous when it infects animals with tamer or slower immune systems like humans.
Whilst in this particular case, the coronavirus resided in snakes until being transmitted to the local population in Wuhan, the researchers note that many other similar types of virus found in bats also pass through an intermediary animal before human infection: SARS was transmitted to humans through the Asian palm civet; Ebola via gorillas and chimpanzees; Marburg through African green monkeys; Nipah via pigs; and Hendra via horses.
Another concerning factor regarding the role of bats in the outbreak of deadly viruses is the increased rate of infection associated with habitat disruption. As the researchers note, disrupting bat habitats appears to increase the stress levels of the animals, making them deposit more of the virus through their saliva, urine and faeces.
"Heightened environmental threats to bats may add to the threat of zoonosis," said Cara Brook, who works with a bat monitoring program funded by the U.S. Defence Advanced Research Projects Agency.
Disease ecologist and UC Berkeley professor Mike Boots adds, "The bottom line is that bats are potentially special when it comes to hosting viruses. It is not random that a lot of these viruses are coming from bats. Bats are not even that closely related to us, so we would not expect them to host many human viruses. But this work demonstrates how bat immune systems could drive the virulence that overcomes this."
The hope is that scientists will be able to apply next generation sequencing (NGS) of genes to track the evolution and spread of viral infections in both animal and human populations. Director of the Programme in Emerging Infectious Diseases at Duke-NUS Medical School in Singapore, Lin-Fa Wang notes that, "Coronaviruses in bats are particularly important to monitor as they remain an important source of emerging infectious diseases."
It is proposed that during times that are outbreak free, known as "peace time" by Wang, scientists should build up large sets of data on different forms of coronavirus so that they can create biochemical probes which track the spread of the virus. One of the issues with using next generation sequencing is that it is only possible to track identified viruses and the bat coronavirus, like all viruses, is constantly changing. If this method is going to be useful to the war against viruses like coronavirus, Wang argues that the library of information will need to be frequently updated, which needs an exceptional volume of resources.
Whilst there is a real fear that the virus will spread across the world to so many people that providing treatment, when developed, will be too difficult logistically, the research discussed here is a step in the right direction towards understanding 2019-nCoV and how scientists, who are risking their own health to study such viruses, should be supported as much as possible.
References:
Bei Li, Hao-Rui Si, Yan Zhu, Xing-Lou Yang, Danielle E. Anderson, Zheng-Li Shi, Lin-Fa Wang, Peng Zhou. Discovery of Bat Coronaviruses through Surveillance and Probe Capture-Based Next-Generation Sequencing. mSphere, 2020; 5 (1) DOI: 10.1128/mSphere.00807-19
Wei Ji, Wei Wang, Xiaofang Zhao, Junjie Zai, Xingguang Li. Homologous recombination within the spike glycoprotein of the newly identified coronavirus may boost cross‐species transmission from snake to human. Journal of Medical Virology, 2020; DOI: 10.1002/jmv.25682
Cara E Brook, Mike Boots, Kartik Chandran, Andrew P Dobson, Christian Drosten, Andrea L Graham, Bryan T Grenfell, Marcel A Müller, Melinda Ng, Lin-Fa Wang, Anieke van Leeuwen. Accelerated viral dynamics in bat cell lines, with implications for zoonotic emergence. eLife, 2020; 9 DOI: 10.7554/eLife.48401