Viruses Derived From Bats Are More Deadly to Humans Due to Their Ability To Fly, Inflammation Tolerance [Study]

Viruses from bats are the most deadly to humans. According to a new study, among the factors that made it worse is the animal's evolution that enabled them to fly.

Bat Diseases Are Worst For Humans

Diseases can occasionally spread from one species to another, including from animals to humans. Researchers have discovered why infections from bats are the most lethal to humans.

According to a new study, this has something to do with its evolution - particularly how it developed the ability to fly. As a result, zoonotic viruses originated from bat hosts have a greater case-fatality rate than viruses from other mammal or bird species. These include SARS and MERS coronaviruses, Hendra and Nipah henipaviruses, Ebola and Marburg filoviruses, and Nipah and Hendra henipaviruses, per Cara Brook, an assistant professor of ecology and evolution at the University of Chicago and the paper's senior author.

According to the study, another factor is the bats' intrinsic ability to tolerate inflammation, which developed along with their flight abilities.

They used a mathematical model supported by empirical data to provide a mechanism for this pattern. In essence, in this model, they showed how a virus could be expected to optimize its within-host virus growth rate by weighing the transmission gains brought on by high virus growth rates against the elevated virulence (disease brought on by these growth rates) that these growth rates incur.

They statistically showed how a few important characteristics of bat physiology and life history, including tolerance of immunopathology/inflammation and robust constitutive immune systems, which are assumed to have evolved in part from the evolution of flying, should select for high-growth rate viruses that can achieve transmission gains without causing extreme virulence to bat hosts.

Bats are, therefore, tolerant of the immunological responses their bodies produce when infected by more virulent viruses with quicker growth rates because of their resilience to inflammation.

The researchers demonstrated how much more dangerous bat-optimized viruses could be than viruses from other mammals using their model to "spillover," or infect, a fictitious human immune system.

They then let these viruses show how high virus growth rates designed for an animal reservoir can cause serious pathology in an immune system from a different species, like a human. Brook noted that it's critical to keep in mind that transmission and virulence of bat viruses trade-off, making it unlikely that viruses with the highest case fatality rates will also generate the greatest number of human infections or, consequently, the greatest burden of human mortality.

While the study predicts that bats and a few other mammalian groups would likely continue to host and be a source of viruses with high growth rates that may become virulent after spreading to humans, these viruses are not expected to be the most contagious either across species (from bat to human) or within the human population after the spillover event.

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Coronavirus Originated From Bats?

According to research, SARS-CoV and MERS-CoV originated in bats. Then, SARS-CoV and MERS-CoV both spread through infected dromedary camels to humans, while SARS-CoV originated in infected civets.SARS-CoV-2, which started the COVID-19 pandemic, has not yet been traced back to its original location.

Based on the available scientific evidence, SARS-CoV-2 most likely developed in nature and then spread to humans or through an unknown animal host. Public health and scientific institutions are making an ongoing international effort to identify the SARS-CoV-2's ancestors, which is crucial for averting pandemics in the future.

Unfortunately, erroneous and misleading claims regarding NIAID-sponsored research on naturally occurring bat coronaviruses have been made because the origins of the SARS-CoV-2 have not yet been determined. These accusations have specifically targeted studies at the Wuhan Institute of Virology in Wuhan, China, supported by a sub-award from NIAID recipient EcoHealth Alliance. Since the naturally existing bat coronaviruses investigated through this sub-award differed genetically from SARS-CoV-2, they could not have been the source of the COVID-19 pandemic.