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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.

US dictionary Merriam-Webster will update the meaning of the word "racism" after being contacted by a Missouri black woman, who claimed the current definition fell short of including the systematic oppression of people of colour, according to media reports.

"A revision to the entry for racism is now being drafted to be added to the dictionary soon, and we are also planning to revise the entries of other words that are related to racism or have racial connotations," according to a statement of the 189-year-old dictionary shared by Kennedy Mitchum, a recent graduate of Drake University in Iowa, on her Facebook.

Mitchum, 22, emailed the dictionary last month, following the death of African American George Floyd in the custody of four Minneapolis police officers, Xinhua news agency reported.

"I kept having to tell them that definition is not representative of what is actually happening in the world," Mitchum told CNN. "The way that racism occurs in real life is not just prejudice, it's the systemic racism that is happening for a lot of black Americans."

Merriam-Webster's first definition of racism is "a belief that race is the primary determinant of human traits and capacities and that racial differences produce an inherent superiority of a particular race."

"It's not just disliking someone because of their race," Mitchum wrote in a Facebook post on Friday. "This current fight we are in is evidence of that, lives are at stake because of the systems of oppression that go hand-in-hand with racism."

Melbourne, Jul 24: Home-made cloth face masks may need a minimum of two layers, and preferably three, to prevent the dispersal of viral droplets associated with Covid-19, according to a study.

Researchers, including those from the University of New South Wales in Australia, noted that viral droplets are generated by those infected with the novel coronavirus when they cough, sneeze, or speak.

As face masks have been proven to protect healthy people from inhaling infectious droplets as well as reducing the spread from those who are already infected, several types of material have been suggested for these, but based on little or no evidence of how well they work, the scientists said.

In the current study, published in the journal Thorax, the researchers compared the effectiveness of single and double-layer cloth face coverings with a surgical face mask (Bao Thach) at reducing droplet spread.

They said the single layer covering was made from a folded piece of cotton T shirt and hair ties, and the double layer covering was made using the sew method described by the US Centers for Disease Control and Prevention (CDC).

The scientists used a tailored LED lighting system and a high-speed camera to film the dispersal of airborne droplets produced by a healthy person with no respiratory infection, during speaking, coughing, and sneezing while wearing each type of mask.

Their analysis showed that the surgical face mask was the most effective at reducing airborne droplet dispersal, although even a single layer cloth face covering reduced the droplet spread from speaking.

But the study noted that a double layer covering was better than a single layer in reducing the droplet spread from coughing and sneezing.

According to the researchers, the effectiveness of cloth face masks is dependent on the number of layers of the covering, the type of material used, design, fit as well as the frequency of washing.

Based on their observations, they said a home made cloth mask with at least two layers is preferable to a single layer mask.

"Guidelines on home-made cloth masks should stipulate multiple layers," the scientists said, adding that there is a need for more research to inform safer cloth mask design.