Bats have been at the center of some of the worst emerging viral zoonoses in recent history. These mammals are responsible for transmitting rabies, Nipah, Ebola, Marburg, SARS, MERS, and likely the novel coronavirus, which has currently infected more than three million people across the world. A recent study explored what makes bats a unique reservoir of rapidly reproducing and highly transmissible viruses.
A multi-institutional team revealed that bats’ fierce immune response to viruses could drive viruses to replicate faster. This explains why the viruses that jump to mammals with average immune systems to humans can wreak havoc. “Some bats are able to mount this robust antiviral response, but also balance it with an anti-inflammation response. Our immune system would generate widespread inflammation if attempting this same antiviral strategy. But bats appear uniquely suited to avoiding the threat of immunopathology,” lead author Cara Brook, Ph.D., a postdoctoral fellow at UC Berkeley, said.
The researchers also found that the bats’ robust interferon system helped viruses persist within them, which also made them live longer. Previous studies revealed that some bat species can live for up to 40 years. However, humans also play a huge role in spreading these viruses. Disrupting a bat’s habitat can stress these animals, making them shed even more virus in their saliva, urine, and feces that can infect other animals.
But, of all viruses that bats carry, researchers found that they have a particularly strong relationship with coronaviruses.
Bats and Coronaviruses
While we have experienced outbreaks from three coronaviruses in recent years, there is so much we need to know about them. Coronaviruses are actually a family of hundreds of viruses, which have already infected many animals such as bats, chickens, camels, and cats. There are times that these viruses undergo what scientists called "cross-species transmission" or "spillover,” where they can mutate in such a way that allows them to start infecting another species.
While the first human coronaviruses were identified in the 1960s, scientists revealed that the first coronavirus was discovered in chickens in the 1930s. And, not all coronaviruses can cause severe respiratory disease. According to Medical Xpress, a web-based medical and health news service that features the most comprehensive coverage in the fields of neuroscience, cardiology, and more, most of us will be infected with a coronavirus at least once in our life. They can be found across the world and are responsible for about 10% to 15% of common colds. Scientists said that seven coronaviruses have the ability to cause disease in humans: four are endemic and usually cause mild disease, while three can cause much more serious and even fatal disease.
A recent study published in PLOS ONE introduced six newly discovered coronaviruses in bats in Myanmar. The findings can help people understand the diversity of coronaviruses in bats and inform global efforts to detect, prevent, and respond to infectious diseases that may threaten public health. The researchers were able to detect these new viruses conducting biosurveillance of animals and people to better understand the circumstances for disease spillover. They focused on sites in Myanmar where humans are more likely to come into close contact with local wildlife due to changes in land use and development. The team managed to collect more than 750 saliva and fecal samples from bats in these areas from May 2016 to August 2018.
After the researchers tested and compared the samples, they estimated that thousands of coronaviruses are present in bats. Many of these aren’t yet discovered. According to Phys.org, an internet news portal that provides the latest news on science, the newly discovered coronaviruses are not closely related to SARS CoV-1, MERS, or SARS-CoV-2. The findings of the study can help future studies better detect potential viral threats to public health.
"Many coronaviruses may not pose a risk to people, but when we identify these diseases early on in animals, at the source, we have a valuable opportunity to investigate the potential threat. Vigilant surveillance, research, and education are the best tools we have to prevent pandemics before they occur,” co-author Suzan Murray, director of the Smithsonian's Global Health Program, said.
Bats and Coronaviruses Are Evolving Together
Bats are natural carriers of coronaviruses. While they don’t appear to be harmful to the bats, there’s potential for them to be dangerous to other animals if the viruses have opportunities to jump between species. A recent study published in Scientific Reports revealed that there’s a deep evolutionary history between bats and coronaviruses. The findings can help scientists develop better public health programs in the future.
While the bat species in this research are different from the one that caused COVID-19, learning about coronaviruses in bats, in general, may improve understanding of the coronavirus causing the current pandemic. The researchers took swab and blood samples from more than a thousand bats of 36 species found on islands in the western Indian Ocean and coastal areas of the African nation of Mozambique. They discovered that 8% of all the bats they tested were carrying a coronavirus.
According to WebMD, the leading source for trustworthy and timely health and medical news and information, the researchers learned that different groups of bats had their own unique strains of coronavirus, revealing that bats and coronaviruses have been evolving together for millions of years. "This is a very rough estimate of the proportion of infected bats. There is increasing evidence for seasonal variation in the circulation of these viruses in bats, suggesting that this number may significantly vary according to the time of the year," Camille Lebarbenchon, Disease Ecologist at the Université de La Réunion, said.
The researchers were also able to build a giant coronavirus family tree, showing how the different kinds of coronavirus are related to each other. They did this by comparing the coronaviruses isolated and sequenced in the context of this study with ones from other animals including dolphins, alpacas, and humans. Steve Goodman, MacArthur Field Biologist at Chicago's Field Museum, said that that there is a deep coexistence between bats and their associated coronaviruses. However, this doesn’t mean that humans should harm them in the name of public health.
“There's abundant evidence that bats are important for ecosystem functioning, whether it be for the pollination of flowers, dispersal of fruits, or the consumption of insects, particularly insects that are responsible for the transmission of different diseases to humans. The good they do for us outweigh any potential negatives,” Goodman said.