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In a study conducted in 117 countries, researchers have found that the world is experiencing the most dramatic reduction in the seismic noise (the hum of vibrations in the planet's crust) in recorded history due to global COVID-19 lockdowns.

Measured by instruments called seismometers, seismic noise is caused by vibrations within the Earth, which travel like waves and the waves can be triggered by earthquakes, volcanoes, and bombs - but also by daily human activity like travel and industry.

This quiet period was likely caused by the total global effect of social distancing measures, closure of services and industry, and drops in tourism and travel, the study published in the journal Science, reported.

The new research, led by the Royal Observatory of Belgium and five other institutions around the world including Imperial College London (ICL), showed that the dampening of 'seismic noise' caused by humans was more pronounced in more densely populated areas.

"Our study uniquely highlights just how much human activities impact the solid Earth, and could let us see more clearly than ever what differentiates human and natural noise," said study co-author Stephen Hicks from ICL in the UK.

For the findings, the research team looked at seismic data from a global network of 268 seismic stations in 117 countries and found significant noise reductions compared to before any lockdown at 185 of those stations.

Researchers tracked the 'wave' of quietening between March and May as worldwide lockdown measures took hold.

The largest drops in vibrations were seen in the most densely populated areas, like Singapore and New York City, but drops were also seen in remote areas like Germany's the Black Forest and Rundu in Namibia.

Citizen-owned seismometers, which tend to measure more localised noise, noted large drops around universities and schools around Cornwall, UK and Boston, US - a drop in noise 20 per cent larger than seen during school holidays.

The findings showed that countries like Barbados, where lockdown coincided with the tourist season, saw a 50 per cent decrease in noise.

"The changes have also given us the opportunity to listen in to the Earth's natural vibrations without the distortions of human input," the study authors wrote.

Earlier in April, a study published in the journal Nature, reported at least a 30 per cent reduction in that amount of ambient human noise since lockdown began in Belgium.

Toronto, May 7: Scientists have uncovered how bats can carry the MERS coronavirus without getting sick, shedding light on what triggers coronaviruses, including the one behind the COVID-19 pandemic, to jump to humans.

According to the study, published in the journal Scientific Reports, coronaviruses like the Middle East respiratory syndrome (MERS) virus, and the COVID19-causing SARS-CoV-2 virus, are thought to have originated in bats.

While these viruses can cause serious, and often fatal disease in people, bats seem unharmed, the researchers, including those from the University of Saskatchewan (USask) in Canada, said.

"The bats don't get rid of the virus and yet don't get sick. We wanted to understand why the MERS virus doesn't shut down the bat immune responses as it does in humans," said USask microbiologist Vikram Misra.

In the study, the scientists demonstrated that cells from an insect-eating brown bat can be persistently infected with MERS coronavirus for months, due to important adaptations from both the bat and the virus working together.

"Instead of killing bat cells as the virus does with human cells, the MERS coronavirus enters a long-term relationship with the host, maintained by the bat's unique 'super' immune system," said Misra, one of the study's co-authors.

"SARS-CoV-2 is thought to operate in the same way," he added.

Stresses on bats, such as wet markets, other diseases, and habitat loss, may have a role in coronavirus spilling over to other species, the study noted.

"When a bat experiences stress to their immune system, it disrupts this immune system-virus balance and allows the virus to multiply," Misra said.

The scientists, involved in the study, had earlier developed a potential treatment for MERS-CoV, and are currently working towards a vaccine against COVID-19.

While camels are the known intermediate hosts of MERS-CoV, they said bats are suspected to be the ancestral host.

There is no vaccine for either SARS-CoV-2 or MERS, the researchers noted.

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"We see that the MERS coronavirus can very quickly adapt itself to a particular niche, and although we do not completely understand what is going on, this demonstrates how coronaviruses are able to jump from species to species so effortlessly," said USask scientist Darryl Falzarano, who co-led the study.

According to Misra, coronaviruses rapidly adapt to the species they infect, but little is known on the molecular interactions of these viruses with their natural bat hosts.

An earlier study had shown that bat coronaviruses can persist in their natural bat host for at least four months of hibernation.

When exposed to the MERS virus, the researchers said, bat cells adapt, not by producing inflammation-causing proteins that are hallmarks of getting sick, but instead by maintaining a natural antiviral response.

On the contrary, they said this function shuts down in other species, including humans.

The MERS virus, the researchers said, also adapts to the bat host cells by very rapidly mutating one specific gene.

These adaptations, according to the study, result in the virus remaining long-term in the bat, but being rendered harmless until something like a disease, or other stressors, upsets this balance.

In future experiments, the scientists hope to understand how the bat-borne MERS virus adapts to infection and replication in human cells.

"This information may be critical for predicting the next bat virus that will cause a pandemic," Misra said.