A scientific study has added a new vector to the usual transportation of viruses and bacteria horizontally from person-to-person: they now can literally fall on you from above.
Every day, more than 800 million viruses fall from the atmosphere and are deposited per square metre at a height of 2,500-3,000 m, the study found. That works out to about 25 viruses for every person in Canada, according to Curtis Suttle, a virologist at the University of B.C. and one of the senior authors of the paper.
Closer to sea level, the numbers would be even higher, Suttle said.
The viruses and bacteria are swept up into the troposphere on dust from soil and spray from the ocean. They hitch a ride on air systems moving above weather, but below the flight paths of jet planes.
Yes, the microbes are alive. But Suttle said they’re really nothing to worry about.
“They’re falling on us all the time,” he said in a phone interview. “For the most part, microbes are our friends. We would be inhaling tens of thousands of viruses a day.”
Viruses tend to be very specific in the species they infect. Viruses that target humans would be pretty-well non-existent, he said.
“We wouldn’t need to worry about them,” Suttle said.
He compared it with going swimming in the ocean. In a teaspoon of water — the amount that you might swallow during a swim — there are as many viruses as there are people in Canada. Unless there are specific contaminants in a body of water, people generally don’t get sick from swimming in the ocean.
“From our perspective, these viruses are absolutely benign,” he said.
The paper by Suttle and colleagues from the University of Granada and San Diego State University was published in the International Society for Microbial Ecology Journal. The data was passively collected during the course of a year on round, slightly-smaller-than-dinner-plate-sized collectors (each one had an exposed area of 667 centimetres squared) in Spain’s Sierra Nevada Mountains.
The study found that deposit rates for viruses were nine to 461 times greater than for bacteria.
Previous studies, Suttle said, have shown that bacteria collected in the same way will grow if added to water. Viruses are different because they need a specific host to infect and grow.
During rain and periods when dust from the Sahara was airborne, deposits of bacteria were significantly higher than deposits of viruses.
Suttle said what’s remarkable is that bacteria and viruses originating in Europe could end up in North America.
“One thing that has always been puzzling is that you find the same viruses and bacteria everywhere you look,” he said. “That’s not intuitive because they live in very specific environments.”
The findings help explain why genetically similar microbes are evenly distributed around the planet.
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