Once inside our body, Covid-19 is difficult to fight, so let’s not let it in! We can protect ourselves, our loved ones, and the general population with one simple gesture: regular hand washing. How can such a simple gesture be effective against such a virulent virus?
What is a virus?
A virus is an object of nanometric size, about 100 nanometers in diameter. It is 100 times smaller than a human cell and 1 million times smaller than a tennis ball. This nanoparticle consists of a viral envelope, formed of a lipid membrane (i.e. fat) and proteins, encapsulating a macromolecule encoding the genome of the virus.
How does soap destroy viruses?
The active ingredients of soap are surfactants, molecules that can be likened to crow’s feet, usable on a nanometric scale to dismantle the virus. These molecules are composed of a part that likes water and another which likes fatty substances, they are called amphiphiles (“Amphi” means “double” in Greek). The membrane of the virus is a fatty substance, such as oil for example.
The hydrophobic part of the surfactants contained in the soap clings to the membrane of the virus and, upon rinsing, the hydrophilic part is attracted to the water molecules. The result of the forces exerted on the virus causes the rupture of its fatty membrane, breaking down the envelope, then the RNA molecule. The virus becomes inactive and is detached from the skin thanks to the action of surfactants, the rubbing of the hands, and the flow of water.
“Do the following experiment: Pour a little oil into the water. The two bodies do not mix. Now add soap and shake. What is going on? Micro drops of oil form in water under the action of soap. These particles are called micelles. In this form, the oil is soluble in water. ”
Why does the virus become inactive after washing my hands with soap?
A virus is not an autonomous organism: it needs a host cell to reproduce. The virus enters it by the same principle as a key in a lock. The S proteins (for Spike in English meaning tip), present in the viral envelope of coronaviruses, bind to certain cellular receptors. The virus is then internalized. Once inside the cell, the “father virus” divides itself into several “son viruses” which will in turn contaminate neighboring cells. Covid-19 is an RNA virus. This means that its genome is encoded as RNA, for ribonucleic acid. RNA, like DNA, is made up of a series of chemical bricks called the nucleotides. Compared to a DNA virus, Covid-19 saves time! Indeed, RNA allows the direct synthesis of proteins, whereas DNA must first be transcribed into RNA before being translated into proteins.
When we wash our hands with soap, as we have seen, the soap dismantles the envelope of the virus. The latter no longer has the key to enter our cells. The viral RNA is also destroyed because it becomes accessible to the surfactants of the soap: in fact, the RNA macromolecule has hydrophobic groups having a strong affinity with the part which likes the fatty substances of the surfactants. These will separate the chemical building blocks of RNA in the same way they act on the lipid membrane of the virus. The virus is now broken down into small parts that will bind to the surfactant molecules in the soap to create micelles, soluble in water.
The same thing happens as when we make the oil-soluble in water by adding soap. In conclusion, washing your hands with soap and water breaks down the virus and robs it of its ability to enter cells, rendering it inactive. It also rids the skin of virus fragments like it does with all other fats (dirt). The World Health Organization (WHO) recommends rubbing your hands for 20 seconds for effective action on the entire surface of the hands.
And the hydroalcoholic gel?
Alcohol in solution in water (60% to 90% by volume) distorts certain proteins in the viral envelope, making the virus unable to enter a cell.
On the other hand, unlike soap which “washes”, the hydroalcoholic gel is not effective on dirty hands. Alcohol is deactivated by the presence of excess fat present on the skin (visible stains). The hydroalcoholic gel should be used on a dry skin, not soiled and without wounds. Thus, WHO recommended handwashing with soap and water when we are at home and the use of hydroalcoholic gel when traveling for errands or work.
Why does the virus attach itself more to certain surfaces than to others?
An infected person can deposit respiratory “droplets”, vectors of the virus, on a surface (plastic, metal, cardboard, human skin). An uninfected person who touches this surface can contract the virus if they then put their hands to their mouth, nose or eyes. A published study in The New England Journal of Medicine in early March 2020 indicates that Covid-19 can be detected for up to 24 hours on cardboard and three days on plastic or stainless steel. Even if the virus stays alive for a while on a surface, very quickly it becomes too weak to infect us effectively. After a few hours it is not probably more active.
Adhesion of viruses to surfaces is mainly done via hydrophobic and electrostatic interactions. The virus has a more or less important affinity with certain types of materials according to its physicochemical properties, for example, the morphology of its envelope, or its “surface charge” which dictates the electrostatic interactions. For now, the link between the physicochemical properties of viruses and the contribution of different interaction forces is not yet well established, but the physics of the main interaction forces involved is known.
Hydrophobic interactions are frequent in our daily life: if you put a drop of water on a table, it is not absorbed by the surface. The coating of the table is hydrophobic and therefore has a good affinity with the lipid membrane of the virus.
To understand electrostatic interactions, we have to think that opposites attract, and that matter is made up of atoms. An atom is made up of positively charged elementary particles – protons – and negatively – electrons. In general, the material is neutral and tends to remain so. This means that it has as many positive charges as there are negative charges. Electrostatic interactions result from the movement of electrons from one body to another. They allow the matter to return to a state of neutrality during a charge imbalance. The chemical composition of a virus’s envelope can give it a neutral, positive, or negative surface charge.
If this charge is negative, the virus will have a good affinity with materials having a positive charge, that is to say that may have a defect of electrons on the surface like paper or nylon. If the surface charge of the virus is positive, it will be attracted to materials that may have excess electrons on the surface. like certain plastics such as PVC or cellophane film.
The development of a vaccine against Covid-19 is a long-term work. Altogether, we are starting a marathon aimed at slowing its spread. By understanding the virus, its physicochemical composition, its mechanisms of action, and its mode of propagation, we also understand the reasons that make barrier gestures effectively in protecting ourselves and others. Let’s put ourselves in the shoes of the virus and we will wash our hands the right way and at the right time.