Postillions are the preferred vector for human-to-human transmission of SARS-CoV-2. While this Covid-19 virus contracts by air, it is one of the unknowns related to this disease, its ability to stay in the air.
Each virus has its own transmission characteristics, which can be divided into three main categories, recalls François Renaud, a biologist in the evolution of infectious diseases: vector transmission, which needs a vector, like the mosquito to infect ( chikungunya, zika…); through contact with human fluids, such as HIV; and by air and postilion. This last category being “the most difficult to control”, underlines this CNRS researcher at the laboratory of infectious diseases of Montpellier.
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Virions, infectious viral particles
SARS-CoV-2 is an encapsulated RNA filament that enters a cell to reproduce there and contaminate others. It then colonizes the cells of the respiratory tract, its preferred target, within which it produces virions, infectious viral particles. When a sick person coughs or sneezes, he “expects a cloud of postillions that are all missiles carrying virions designed within the respiratory system,” said the biologist. “These postlets are also expelled when we speak, in smaller quantities but also potentially contagious,” said Christophe Bécavin, specialist in the mechanisms of entry of the virus into the body.
A healthy person will therefore become infected by inhaling the droplets emitted by someone contaminated. The Covid-19 can also be contracted by “handling” when an infected droplet falls on an object that is touched, before bringing our hand to the level of our mucous membranes.
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Shields
Can a single postilion suffice to infect? “We don’t know, because we still don’t know what the minimum charge is to catch Covid-19,” said Christophe Bécavin, a CNRS researcher at the Institute for Molecular Pharmacology. Likewise, if a postilion lands on a surface, it will be infected more or less long depending on the material, the “quality” of the virus contained in the droplet decreasing over time.
Can the virus survive as an aerosol? The American Academies of Science recently shared information tipping the scales in favor of transmitting the virus through bioaerosols, rather than just droplets sprayed directly onto the face or surfaces. In a study, researchers from the University of Nebraska notably found portions of the genetic code of the virus in the air expelled by Covid-19 patients. “They found virus RNA after two hours. We do not know, however, if he was still infectious, “said Christophe Bécavin.
Many doctors, as well as the Academy of Medicine, recommend the widespread use of the mask covering the mouth and nose. “We have to start from the most unfavorable hypothesis,” argues Dr Rochoy, co-initiator of the “Stop postillons” collective.
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