Every day, millions of viruses and bacteria travel through the atmosphere. Researchers recently discovered that these viruses can be transported aloft and fall thousands of miles to the ground.
It’s not just rain or snow falling from the sky. According to a new study carried out by American, Canadian and Spanish researchers, the viruses present in the air would cling to the terrestrial layers located above us at several kilometers of altitude, before falling back on the earth. This work has been published in review International Society for Microbial Ecology Journal.
Up to 7 billion square bacteria per day
These findings confirm what we already knew, which is that viruses are not only present in water and soil, but also in the air. The authors of this study, however, took their research further, since they sought to determine how many viruses could be transported between 2,500 and 3,000 meters above sea level.
A team of Spanish researchers has placed sensors above the planetary boundary layer (interface zone between a body and the fluid) in the Sierra Nevada mountains, in the United States. Their research indicated that between 260 million and 7 billion square bacteria are deposited per day and per meter on the troposphere (layer of the Earth’s atmosphere located closest to the surface of the globe). The virus deposition rate is therefore 9 to 461 times higher than that of bacteria, scientists say.
How do bacteria cling in the air?
According to the researchers, these viruses remain attached to the atmosphere thanks to small organic particles and dust in the air but also fine rains such as spray, which facilitate transfer from one region to another. “Bacteria and viruses are usually deposited on Earth by rainy episodes and Saharan dust intrusions. However, rain is less effective in removing viruses from the atmosphere,” explains Isabel Reche, from the University of Granada. (Spain).
Some of these viruses can protect humans
This phenomenon would explain why we find identical genetic viruses in remote geographical areas. Curtis Suttle, virologist, University of British Columbia and one of the lead authors of the study explains: “This preponderance of viruses that travel through the atmosphere probably explains why it is possible to find a virus on a continent, before to see it land on another. “
The figures may appear alarmist, even catastrophic. Yet not all of these millions of viruses are inherently bad. Scientists, for example, have detected certain bacteriophages, i.e. viruses that kill bacteria that are harmful to humans and the environment.
“Significant downflows of bacteria and viruses from the atmosphere can have positive effects on the structure and function of receiving ecosystems. This could be likened to a kind of seed bank allowing ecosystems to adapt quickly to environmental changes ”, underline the latter in the conclusions of their study.
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