Is this disinfection really effective？ Let’s see how Covid-19 was inactivated.

shell of nuts

The following article comes from Guoke Children’s Academy, written by Xiao Tian.

In recent days, the epidemic situation in COVID-19 has been raging. At present, the number of new cases is still rising, and the cumulative number of confirmed cases has exceeded 70,000. The situation is still very grim.

Although there have been many articles on popular science home disinfection, there are still many people who are not at ease and often come to ask, is this disinfection effective? Can you kill Covid-19?

This article pushed by Nut Mom today, starting from the mechanism of disinfectant, makes you clear about the inactivation process of get virus, and at the same time, you are no longer anxious and calm!

one

Structural characteristics of Covid-19.

Novel coronavirus, which caused the pneumonia epidemic, has been identified as an enveloped virus. Besides the capsid formed by protein and its genetic material (single-stranded RNA), it also has an envelope.

Schematic diagram of Covid-19 structure

On the surface of the envelope structure, there are three kinds of glycoproteins, namely:

Spike glycoprotein (S, SpikeProtein, receptor binding site, cytolysis and major antigen site)

Small envelope glycoprotein (e, EnvelopeProtein).

Membrane glycoprotein (M, MembraneProtein, responsible for transmembrane transport of nutrients, budding release of newborn virus and formation of virus envelope)

Covid-19 electron micrograph

If disinfectants, or other environmental conditions, can destroy the structure of Covid-19, it should be able to effectively inactivate it.

2

The Mechanism of Common disinfection products

At present, disinfection products on the market can be classified according to the site of action, which can be summarized into the following two categories:

Nucleic acid directly acting on internal genetic material: ultraviolet disinfection

Protein is inactivated by most chemical disinfectants and high temperature.

The deactivation of protein mainly changes and destroys its secondary or tertiary structure by heating, dehydration, oxidation, salification, deamination and charge change.

three

How to choose an effective disinfection products?

one

Direct destruction of RNA

Representative products: ultraviolet lamp, ultraviolet disinfection cabinet.

Common disinfection lamp products

Ultraviolet is an electromagnetic wave, which can be generally divided into:

UVA (ultraviolet a, wavelength 320 ~ 400 nm, long wave)

UVB (wavelength 280 ~ 320 nm, medium wave)

UVC (wavelength 100 ~ 280 nm, short wave)

It should be pointed out that the wavelength below 200nm is vacuum ultraviolet, which can be absorbed by air. Therefore, the wavelength that UVC can pass through the atmosphere is between 200 ~ 280 nm, which is also the wavelength band selected by UV lamps in the market at present. Among them, the sterilization effect is the strongest at 253.7nm.

After Covid-19 is irradiated with UVC, it can undergo photochemical reaction with its genetic material RNA, causing the cleavage of phosphodiester bond and hydrogen bond, forming pyrimidine dimer (such as uracil cyclobutane dimer, uracil hydrate, cytosine hydrate, etc.), thus causing the virus to lose its replication ability.

Ultraviolet lamp disinfection, although effective, is not recommended.

matters need attention

Purchase ultraviolet lamps with 253.7 nm wavelength for disinfection and sterilization (different from decorative ultraviolet lamps, etc.);

Ultraviolet ray penetration is poor, so it should be directly irradiated on the surface of the object during sterilization and disinfection, and the distance from the irradiated object should not exceed 1 meter.

When disinfecting indoors, doors and windows should be closed, and personnel should avoid it. The irradiation time should be not less than half an hour, and after disinfection, it should be fully ventilated.

Ultraviolet rays can damage the skin and cornea, so people should not directly touch or stare, especially children.

2

Destroy protein and inactivate it.

01

Physical heating

Representative products: steam disinfection cabinet/pot/machine, etc.

Common steam boiler

This kind of products use the high temperature of water vapor to break the disulfide bonds and hydrogen bonds in the protein molecule of the virus to destroy its secondary structure; Peptide bonds will also break after a long time.

In this way, protein will change from a regular spiral, spherical and other spatial structures to an irregular extended peptide chain, resulting in irreversible inactivation.

This kind of products are mainly aimed at some heat-resistant items, such as tableware, toys, baby bottles and other small items. It is not recommended to buy it. Boil it directly in a pot or steam it in a steamer, and the same effect can be achieved.

It should be noted that for Covid-19, the temperature should be at least 56℃, and the disinfection time should be at least half an hour to ensure that the virus is fully inactivated.

02

dehydrate

Representative products: medical alcohol

Ethanol (commonly known as alcohol) can kill viruses with envelope structure, so it is effective for Covid-19 this time.

Specifically, alcohol has a certain fat solubility, and according to the principle of "similar compatibility", it can destroy the lipid envelope composed of phospholipid bilayer; At the same time, protein can be dehydrated and denatured when it comes into contact with glycoprotein on the surface of virus envelope, thus inactivating the virus.

It should be emphasized that the reason why 75% alcohol is used is that when the alcohol concentration is too high, the dehydration reaction will be too fast, which will cause the protein in contact to condense rapidly, thus forming a protective dura mater on the surface of the virus to prevent further infiltration of alcohol. When the concentration is too low, it is not enough to kill the virus.

At the concentration of about 75%, the antivirus effect is the best. Alcohol will dissolve the protein envelope first, and then penetrate into the virus a little bit to degrade the genetic material.

The concentration of medical alcohol in the market is mostly 95% and 75%, and the latter has better disinfection effect. If it is the former, it can be diluted with water (100 ml of 95% alcohol and 27 ml of distilled water) to make about 75% alcohol.

If you can’t buy medical alcohol, more than 75% liquor can also be used to disinfect the surface of objects, but because there are other substances besides ethanol, the effect is definitely not as good as medical alcohol. This is an emergency measure and is not recommended for long-term use.

When in use, the alcohol solution can be sprayed in a watering can, or it can be wiped with an alcohol cotton ball made of cotton swabs. Hands, mobile phones, remote controllers, door handles, buttons, keys, keyboards and mice can all be disinfected with it.

matters need attention

Don’t spray alcohol on infants, avoid touching a lot of alcohol on the body, and prevent allergies or alcoholism;

When using alcohol, don’t be close to the heat source, and don’t spray directly into the air to avoid fire;

Do not spray alcohol on clothes to prevent static electricity from causing fire;

When disinfecting the surface of electrical appliances, remember to cut off the power supply, and all items should be reused after the alcohol volatilizes;

Alcohol should be stored in a dark, cool and ventilated place to avoid children’s contact.

03

oxidate

Representative product 1: chlorine-containing disinfectant

All chlorine-containing disinfectants have one thing in common-they can generate hypochlorous acid (HClO) with microbicidal activity after being dissolved in water.

Hypochloric acid has a small molecular weight and strong oxidizing property. When it comes into contact with Covid-19, it will first oxidize the envelope protein to denature it, and at the same time damage its protein shell, so that its protein cross-linking function will be lost, thus further destroying the biological enzyme system and genetic genes and making it inactive.

Common chlorine-containing disinfectants in the market include bleach, bleach, 84 disinfectant, etc., which can be used for household daily necessities (such as tables and chairs, bedside tables, sanitary ware, door and window handles, etc.). It should be pointed out that not all disinfection products with the word "chlorine" are chlorine-containing disinfectants.

Although the main components of this chlorine-containing disinfectant are different, here is a trick for everyone: the main components of the product are "sodium hypochlorite" or "calcium hypochlorite", that is, chlorine-containing disinfectant (of course, the main components of chlorine-containing disinfectant also include hypochlorous acid, trisodium phosphate chloride, sodium dichloroisocyanurate, trichloroisocyanuric acid, chloramine, etc., but the first two are commonly used in household products).

When using, some solid disinfectants (such as bleaching powder) need to be prepared into a solution with a specified concentration for use; Liquid disinfectants (such as 84 disinfectant) need to be diluted with water in a certain proportion before use. Just follow the instructions.

matters need attention

Chlorine-containing disinfectants are generally irritating to some extent, so masks and gloves should be worn and protected when configuring and repackaging;

Chlorine-containing disinfectants are highly oxidizing, so they should be stored away from high temperature, fire sources and children.

Chlorine-containing disinfectants should avoid contact with metal objects and colored clothes to avoid corrosion or fading;

In particular, it should be noted that chlorine-containing disinfectants should not be used with alcohol or toilet cleaner at the same time, which will produce toxic gases and cause harm to human body.

Representative product 2: peroxide disinfectant

Peroxide disinfectant refers to a kind of disinfectant which contains divalent peroxy group "-O-O-" in its molecular structure and can produce active oxygen with bactericidal ability, and the representative is peracetic acid.

It also kills Covid-19 because of its strong oxidizing ability. When exposed to the virus, it can be damaged by removing the electrons of the virus envelope protein, and it can also attack the nucleotide base and sugar-phosphate skeleton, thus destroying the biological structure and function of the virus.

Besides peracetic acid, peroxide disinfectants also include hydrogen peroxide (hydrogen peroxide) and chlorine dioxide.

This is a kind of safe and green disinfectant. Among them, the products containing peracetic acid have the pungent smell of acetic acid, which are mostly used for industrial and agricultural disinfection, and are generally not recommended for household use. Hydrogen peroxide is very suitable for home use, and can be used on tables, nightstands, sanitary ware, door and window handles, stair handrails and other surfaces.

When in use, according to the national standard GB26371-2010 hygienic standard for peroxide disinfectants, "on the surface of general objects, use 0.1% ~ 0.2% peracetic acid or 3.0% hydrogen peroxide for disinfection for 30 minutes, and then rinse with clear water to remove residual disinfectants", or operate according to the product instructions.

matters need attention

Peroxide disinfectants are highly oxidizing and irritating to skin and mucosa, so be careful not to let children touch them.

Peroxide disinfectants should be stored in a ventilated and cool place to avoid high temperature and metal to prevent explosion danger;

Hydrogen peroxide is unstable, and its disinfection ability will fail if it is stored for a long time. Therefore, it is recommended to store it in the dark and seal it tightly, and use it as soon as possible after opening.

It is worth mentioning that disinfection products (such as Di Lu, Verus, etc.) whose main component is "p-chloroxylenol" is controversial at present.

Dew disinfectant

P-Chloro-m-xylenol (PCMX for short) belongs to phenolic disinfectant, and there are few reports on its action on coronavirus. According to the experimental results in recent years, this kind of disinfectant is effective for SARS-CoV SARS virus, human coronavirus 229E and MHV coronavirus.

In view of the high homology between Covid-19 and SRAS virus, we infer that the disinfectant containing p-chloroxylenol may have a killing effect on novel coronavirus.

The best effective concentration of p-chloro-m-xylenol is 0.12%, and the specific products can be used according to the instructions or diluted with water.

Another one that is discussed more is the ozone machine.

Ozone machine, picture from Amazon.

In terms of mechanism, the strong oxidation of ozone is effective for viruses. Previously, there have been experimental reports on the inactivation of SARS virus by active oxygen and ozone, and a high inactivation efficiency has been achieved.

However, ozone is highly irritating, unstable in chemical properties, harmful to human body due to poor dose control, and the official has not given a clear conclusion at present, so it still needs to be used as a home disinfection method as appropriate.

That’s the summary of all the effective disinfection products for Covid-19. In view of the current outbreak of pneumonia, experts from the Health and Health Commission pointed out: "Disinfection is an important means to cut off the route of transmission and control the epidemic of infectious diseases."

I hope everyone will do a good job in home protection and scientific disinfection, so that the virus has no chance.

– END –

Author | Xiao Tian, mother of a four-year-old girl, master of biology, working mother, parent-child freelance writer; I like to record the baby’s growth in words and practice raising daily life with scientific concepts.

Editor | Octopus Mom, the mother of a two-year-old boy

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Original title: "Is this disinfection really effective? How on earth was Covid-19 inactivated? 》

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