High in the Sierra Nevada mountains of Spain, an international team of researchers set out four buckets to gather a shower of viruses falling from the sky.
Scientists have surmised there is a stream of viruses circling the planet, above the planet’s weather systems but below the level of airline travel. Very little is known about this realm, and that’s why the number of deposited viruses stunned the team in Spain. Each day, they calculated, some 800 million viruses cascade onto every square meter of the planet. Most of the globe-trotting viruses are swept into the air by sea spray, and lesser numbers arrive in dust storms.
“Unimpeded by friction with the surface of the Earth, you can travel great distances, and so intercontinental travel is quite easy” for viruses, said Curtis Suttle, a marine virologist at the University of British Columbia. “It wouldn’t be unusual to find things swept up in Africa being deposited in North America.”
The study by Suttle and his colleagues, published this year in the International Society of Microbial Ecology Journal, was the first to count the number of viruses falling to earth. The research, though, is not designed to study influenza or other illnesses, but to get a sense of the virosphere, the world of viruses on the planet.
Generally it’s assumed these viruses originate on the planet and are swept upward, but some researchers theorize that viruses may originate in the atmosphere. (There is a small group of researchers who believe viruses may even have come here from outer space.)
Whatever the case, viruses are the most abundant entities on the planet by far. While Suttle’s team found hundreds of millions of viruses in a square meter, they counted tens of millions of bacteria in the same space.
Mostly thought of as infectious agents, viruses are much more than that. It’s hard to overstate the central role that viruses play in the world: They’re essential to everything from our immune system to our gut microbiome, to the ecosystems on land and sea, to climate regulation and the evolution of all species. Viruses contain a vast array of unknown genes — and spread them to other species.
Last year, three experts called for a new initiative to better understand viral ecology. “Viruses modulate the function and evolution of all living things,” wrote Matthew B. Sullivan of Ohio State, Joshua Weitz of Georgia Tech, and Steven W. Wilhelm of the University of Tennessee. “But to what extent remains a mystery.”
Do viruses even fit the definition of something alive? While they are the top predators of the microbial world, they lack the ability to reproduce and so must take over the cell of a host — called an infection — and use its machinery to replicate. The virus injects its own DNA into the host; sometimes those new genes are useful to the host and become part of its genome.
Researchers recently identified an ancient virus that inserted its DNA into the genomes of four-limbed animals that were human ancestors. That snippet of genetic …read more