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  • ♪♪♪

  • - All viruses carry

  • some kind of genetic material, DNA or RNA.

  • COVID-19's genetic material is RNA

  • encased by a protective shell called a capsid.

  • This is all surrounded by an envelope made of lipids

  • which are essentially fats and proteins.

  • Spike proteins protrude out of the virus.

  • The RNA has all the instructions

  • for how this virus needs to replicate

  • if it had the proper machinery,

  • but it lacks this machinery to replicate

  • so it has to infect a cell.

  • Once the virus enters your body,

  • it looks for cells with the right receptors.

  • Specific spike proteins

  • bind to a specific type of receptor called ACE2

  • which stands for angiotensin-converting enzyme 2.

  • When the virus binds to this receptor on a cell,

  • it's then able to enter and release its RNA into the cell.

  • The cell has its own replication machinery like a ribosome

  • for making its own RNA into protein.

  • But now, the virus can hijack the cell's ribosome

  • and turn its own viral RNA into protein

  • that makes up the components necessary for a new virus.

  • Essentially, it turns the cell into a virus-making machine

  • and in the process destroys the cell.

  • Once it makes a ton of virus,

  • it breaks out of the cell destroying the cell

  • and all the new viruses will move on to other cells

  • to repeat the process.

  • So how does infection lead to the common symptoms

  • of fever, cough, and difficult in breathing?

  • ACE2 is found especially on cells

  • that line the upper respiratory tract

  • called goblet cells and ciliated cells.

  • These cells are the front-line defenders.

  • Goblet cells produce mucus

  • which traps bacteria and pathogens.

  • Ciliated cells then sweep the debris and mucus out

  • clearing away the unwanted particles.

  • When the virus attacks goblet and ciliated cells,

  • this causes inflammation and irritation in the airways

  • that will stimulate dry coughs.

  • If you're healthy, chances are your immune system

  • will be able to eventually fight off the infection here

  • before it's able to spread down

  • to the lower respiratory tract.

  • But if your immune system can't stop it

  • in the upper respiratory tract,

  • the virus will travel down to invade the lungs

  • and specifically to alveoli.

  • Alveoli are air sacs in the lungs

  • where gas exchange between O2, oxygen,

  • and CO2, carbon dioxide, occur.

  • The virus attacks the cells in the alveoli

  • and when the body detects the virus,

  • it signals an immune response that go into overdrive.

  • Immune cells are sent to the alveoli

  • which cause them swell and fill with fluid.

  • The overactive immune response

  • can damage more alveolar cells

  • causing more cells to die and slough off

  • filling the lungs with more debris and fluid.

  • This interrupts the proper transfer of oxygen

  • into the bloodstream

  • and causes alveoli to eventually collapse.

  • This is why difficulty in breathing

  • is one of the symptoms of COVID-19 infection.

  • Additionally, specific proteins are released

  • as an immune response into the blood

  • where they travel up to the brain

  • to a region called the hypothalamus.

  • One of the things the hypothalamus regulates is temperature.

  • The protein signals your hypothalamus

  • to increase body temperature leading to fever.

  • Less oxygen in your blood may mean your vital organs

  • don't have enough oxygen to keep working.

  • This can lead to organ failure causing them to shut down.

  • Respiratory viruses like COVID-19

  • are spread by respiratory droplets

  • that are released when someone coughs or sneezes.

  • These droplets can stay aloft for six feet

  • so they can easily be transmitted

  • to somebody standing nearby breathing in those droplets

  • or the droplets can land on surfaces

  • and survive on surfaces for around 24 hours.

  • The virus can then be transmitted by touching those surfaces

  • and then touching your nose, eyes, or mouth.

  • The incubation period is the time of infection

  • to appearance of symptoms

  • and it can be anywhere from two to 14 days.

  • This means you could be infected and show no symptoms.

  • But if you're not social distancing,

  • you will go on to infect others

  • without even knowing you're sick yet.

  • Soap may seem too simple to work against such a tough virus

  • but it actually does.

  • Soap has molecules that have a hydrophilic head,

  • meaning it's attracted to water,

  • and a hydrophobic tail that's repelled by water

  • and attracted to oil.

  • When you mix soap and water,

  • the hydrophobic parts are attracted to the oil particle

  • you're trying to wash off.

  • They stick to the oil particle

  • and when you rinse with water,

  • the hydrophilic parts follow the water

  • taking along with it the oily substance.

  • Remember that viruses have an outer envelope

  • that consist of lipids which act like oils.

  • Soap breaks apart the virus and gets it off your hands.

  • But it takes 20 seconds for this to completely work.

  • So far, testing is done by collecting samples from patients

  • using nasal swabs.

  • RNA is extracted from that nasal swab sample.

  • Since RNA is the genetic information of the virus,

  • it can be used to identify the virus

  • just like how our DNA is unique to identifying us.

  • Once the RNA is extracted,

  • scientists add an enzyme called reverse transcriptase

  • to turn the RNA into DNA.

  • Next, they use a polymerase chain reaction, or PCR,

  • to make more copies of the DNA.

  • To do this, scientists add primers

  • which are short sequences that can be designed

  • to attach only to fragments

  • that make the sample DNA uniquely COVID-19.

  • Fluorescent dyes are added in the mix

  • and fluorescence will correspond

  • to how much of that identifying fragment

  • is preset in the sample.

  • Thus, the amount of fluorescence

  • tells us the amount of virus in that sample.

  • If there's no virus, you'll get virtually no fluorescence.

  • While vaccines and potential treatments

  • are still being developed,

  • those infected may need supportive care in severe cases.

  • Supportive care means using ventilators

  • to help patients breathe and treating complications

  • resulting from a distracted weakened immune system.

  • But there's only so many ventilators

  • and hospital beds available.

  • If everyone gets sick at the same time,

  • we won't have enough resources, hospital beds,

  • doctors and nurses able to help everyone who needs it.

  • This is why spreading out the rate of infection

  • is so critical to allowing our healthcare system

  • to not become oversaturated.

  • This is why you've probably heard

  • that flattening the curve is so important.

  • That curve refers to the huge influx of cases

  • we're seeing without preventative measures being followed

  • like quarantining and social distancing.

  • If everyone gets sick in a short period of time,

  • this quickly over saturates the healthcare system,

  • meaning we won't have enough resources

  • to save the lives of those who can die from this infection.

  • But if everyone stays home,

  • we can delay the number of cases over time

  • and help keep the healthcare system from over saturating

  • so we can help as many people as possible.

  • How do epidemiologists describe how contagious a disease is?

  • For example, if one existing infection

  • will cause one more new infection and so on,

  • this would be an R-naught of one.

  • If an R-naught is over two,

  • that means every one infection

  • can cause two more infections.

  • So why is COVID-19 such a big deal?

  • For comparison, the average R-naught of the seasonal flu

  • is around 1.3.

  • The R-naught of the devastating 1918 Spanish flu was 1.8.

  • The R-naught of COVID-19 is estimated to be 2.2.

  • Even if we round down to two,

  • you can see how quickly just one infected person

  • can spread the virus to tons of people.

  • But if just one person

  • takes their social responsibility seriously and stays home,

  • look how much spread they can prevent.

  • This is why everyone needs to follow the CDC guidelines

  • and stay home so we can delay the number of cases.

♪♪♪

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Covid-19。 圖解科學摘要 (Covid-19: An Illustrated Scientific Summary)

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    致平馬 發佈於 2021 年 01 月 14 日
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