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A team of scientists are calling for further research into how sunlight inactivates SARS-CoV-2 after realizing there is a glaring gap between the most recent theory and experimental results.
UC Santa Barbara mechanical engineer Paolo Luzzatto-Fegiz and his colleagues noticed that the virus was inactivated up to eight times faster in experiments than the most recent theoretical model predicted.
“The theory assumes that inactivation works by having UVB hit the virus’s RNA, damaging it,” Luzzatto-Fegiz explained.
But the gap suggests that something more is going on, and understanding what it is may be helpful in dealing with the virus.
UV light, or the ultraviolet part of the spectrum, is readily absorbed by certain nucleic acid bases in DNA and RNA, which can cause them to bind in ways that are difficult to fix.
But not all UV rays are the same. Longer UV waves, called UVA, don’t have enough energy to cause problems. It is the mid-range UVB waves in sunlight that are primarily responsible for destroying microbes and endangering our own cells by the sun.
Shortwave UVC radiation has been shown to be effective against viruses such as SARS-CoV-2, although it is still safely enveloped in human fluids.
But this type of UV does not usually come into contact with the Earth’s surface, thanks to the ozone layer.
“UVCs are great for hospitals,” said Julie McMurry, co-author and toxicologist at Oregon State University. “But in other environments – for example, kitchens or subways – UVC would interact with particles to produce harmful ozone.”
In July 2020, an experimental study tested the effects of UV light on SARS-CoV-2 in simulated saliva. They noted that the virus was inactivated when exposed to simulated sunlight for 10 to 20 minutes.
“Natural sunlight can be effective as a disinfectant for contaminated non-porous materials,” Wood and colleagues concluded in the article.
Luzzatto-Feigiz and his team compared the results to a theory of how sunlight got there, published just a month later, and found that the calculations didn’t match.
This study found that the SARS-CoV-2 virus was three times more sensitive to UV sunlight than influenza A, with 90% of the coronavirus particles inactivated after only half an hour of exposure to sunlight. midday sun in summer.
By comparison, in winter, light infectious particles could remain intact for days.
Environmental calculations performed by a separate team of researchers concluded that the virus’s RNA molecules were directly photochemically damaged by light rays.
This is achieved more powerfully by shorter wavelengths of light, such as UVC and UVB. Since UVC does not reach the Earth’s surface, they based their calculations of environmental light exposure on the mid-wave UVB portion of the UV spectrum.
“The inactivation observed experimentally in simulated saliva is more than eight times faster than theory would have expected,” wrote Luzzatto-Feigiz and his colleagues.
“So scientists don’t yet know what’s going on,” Luzzatto-Fegiz said.
The researchers suspect that it is possible that instead of directly affecting RNA, long-wave UVA rays interact with molecules in the test medium (simulated saliva) in a way that speeds up virus inactivation.
Something similar is seen in wastewater treatment – where UVA reacts with other substances to create molecules that damage viruses.
If UVA can be harnessed to combat SARS-CoV-2, inexpensive and energy-efficient wavelength specific light sources could be useful to augment air filtration systems at relatively risk. low for human health.
“Our analysis highlights the need for additional experiments to separately test the effects of specific light wavelengths and average composition,” concludes Luzzatto-Fegiz.
With the ability of this virus to remain airborne for long periods of time, the surest way to avoid it in countries where it is rife is still through social distancing and wearing masks where distancing is not possible. is not possible. But it’s good to know that sunlight can help us in the warmer months.
Their analysis was published in The Journal of Infectious Diseases.
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