字幕列表 影片播放 列印英文字幕 ♪♪♪ - 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.