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How to correctly understand new coronary pneumonia?

1343 2020.03.27

How did this sudden outbreak of new coronavirus pneumonia occur and spread? What is the rate of death and transmission? How to reduce the possibility of infection?

Part 1 Infection

First we need to know how the virus infects patients.

For a virus to enter a cell, the cell must have its corresponding receptor (Receptor). For example, the common receptor for HIV is CD4 protein, which is usually on the surface of immune cells in the blood, so HIV can be transmitted through the blood without worrying about air transmission.

The receptor for the new coronavirus is angiotensin-converting enzyme 2 (ACE2). This means that for the virus to infect humans, it must first contact cells with the enzyme to complete receptor binding.

And we happen to have a lot of these cells exposed to the air-the mucosa.

The significance of the mucosa is to secrete mucus and keep it moist.

There are a lot of mucosal cells in our lips, eyelids, nasal cavity and oral cavity. When the virus contacts your oral mucosa in some way and binds with the receptor, the infection begins.

In order for you to understand what happened next, we have made a simplified rough process.

First, the envelope of the coronavirus fuses with the cell membrane, releasing viral genetic material—a single strand of RNA.

This RNA can be used directly as messenger RNA, tricking the ribosome in the cell to synthesize RNA replicase.

The RNA replicase will generate the negative RNA strand based on the viral RNA. This negative strand will continue to generate more viral RAN fragments and positive RNA strands with the replicase. These different RNA fragments will generate more different viral protein structures with the ribosome. .

Finally, the protein coat and RNA combine to form new coronavirus particles, which are secreted out of the cell through the Golgi apparatus and infect new cells.

Each infected cell produces thousands of new virus particles that spread to the trachea, bronchi, and eventually reach the alveoli, causing pneumonia.

After the infection is complete, transmission is not difficult. The saliva secreted by your three pairs of salivary glands will be mixed with respiratory secretions from the throat and other parts, allowing the virus-laden saliva to spread into the air with your sneeze and cough, and to contact other people's mucous membranes.

Mucosal infections and droplets spread, which is why coronaviruses spread so easily.

Part 2 Spread

The first is a sneeze. You will spit out more than 10,000 droplets, reaching a distance of up to 8 meters.

Then there is a cough, 1000-2000 droplets, up to 6 meters.

In the end, even quiet speech produces about 500 droplets per minute.

They quickly evaporate in the air and become smaller, becoming dry droplet nuclei. The epithelial cells are proteins that coat the coronavirus and float in the air, touching other people's mucous membranes.

Part 3 Masks

Wearing a mask is certainly a good way. The multilayer structure of the mask can effectively block large particles, and those nano-sized particles will be adsorbed on the internal fibers due to electrostatic effects.

So if we take the diameter of the particles as the abscissa and the filtering efficiency as the ordinate, the filtering effect of these masks is actually a U-shaped curve. .

It can be seen that the most difficult to filter is actually particles with a diameter of about 0.3 microns. This is why most masks use the 0.3 micron sodium chloride filtration capacity as a test indicator, and it is N95 that can filter more than 95% in the test.

N95's filtering effect is of course the best, but even the worst gauze masks can achieve close to 80% protection for particles above 10 microns, which is about one-tenth of our hair diameter.

How big is the size of the droplet core?

According to a 2007 paper, 82% of the droplet nuclei produced by cough are concentrated in 0.74-2.12 microns.

Looking at it this way, most ordinary nuclear medical masks are sufficient for droplet droplets. In a randomized trial involving more than 2,800 flu medical staff in the United States, the infection rate of influenza wearing N95 masks and medical masks was not even significant. difference.

Therefore, don't worry about the complicated mask types, brands and national standards. Rather than wearing N95, more importantly: did you wash your hands?

Wash your hands because your hands are likely to have a coronavirus alive.

Then when you rub your eyes and pick up booger, the virus will contact the mucous membrane cells and complete the infection.

So, wash your hands. Wash a little longer.

Part 4 courage

After the outbreak, many institutions have also released estimates of the R0 value of new coronaviruses, most of which are between 2-3.

R0 (Basic reproduction number) means the average number of people infected with a single infection without intervention.

The R0 of the new coronavirus is 2-3, meaning that each infected person will transmit the virus to 2-3 people. This is why pneumonia started to erupt early.

But with the strong intervention of the external environment, this average number of infections will start to decrease, and this plague will make all of us nervous.

As long as we step out of the house, go to the construction site, go to the office building, go to the assembly line, the risk already exists.

Of course, we should reduce the probability of bad luck as much as possible, but we praise courage because we humans always choose to do what we should when we know the risks.

Finally, let's take a look at the protagonist of this pneumonia-this deformed sphere with a diameter of about 0.1 microns.

Terrible? We already know its RNA sequence, its infection mechanism, transmission mechanism, clinical manifestations and lethality.

It's not that scary.

If we are scared, scared to lock up our neighbors, scared to attack strange helpers, scared to make everyone dare not speak in the name of rumors. That's really scary.

The praise of humanity is a praise of courage, praising all those who are still working hard, and hope that in the new year, we can all have more courage.