B2 中上級 2029 タグ追加 保存
By now you've probably heard of COVID-19, or coronavirus disease discovered in 2019,
which is responsible for a global pandemic. Thus far the main country affected has been
China, but it has spread to a number of other countries around the world to a varying degree.
The virus was initially referred to as the 2019-nCoV, or the 2019 novel coronavirus and
was informally called “Wuhan coronavirus”. The World Health Organization named the disease
COVID-19 because it doesn't refer to a geographical location, an animal, a person or group of
people - all of which can lead to stigma. They also wanted to make it pronounceable
and related to the disease - not an easy task! The virus was officially named SARS CoV-2,
or severe acute respiratory syndrome coronavirus 2, because it's genetically very similar
to the SARS coronavirus which was responsible for…well the Severe Acute Respiratory Syndrome,
or SARS, outbreak in 2002. So SARS-CoV-2 causes COVID-19.
Now, coronaviruses that circulate among humans are typically benign, and they cause about
a quarter of all common cold illnesses. But occasionally, coronaviruses that circulate
in an animal reservoir mutate just enough to where they're able to start infecting
and causing disease in humans, if they're given an opportunity. In 2002 SARS was a coronavirus
that hopped over from bats to civets, which is a cat-like mammal; and then over to humans.
And in 2012, there was MERS, which was a coronavirus that hopped over from bats to camels a few
decades ago and then circulated among camels for quite some time before infecting humans.
COVID-19 most likely also started with bats, but this time the intermediate host was probably
a pangolin, an animal that looks like a cross between an anteater and an armadillo. That's
based on the fact that scientists identified a coronavirus in pangolins that's a 96%
genetic match to SARS-CoV-2. Sadly, pangolins are heavily trafficked around the planet,
largely because people believe that their scales have healing properties. Because they're
moved around the world rather than left in the wild, there are ample opportunities for
a coronavirus to go from a pangolin to a human.
As of February 11, 2020, there have been 43,103 cases of COVID-19 and 1,018 deaths, with a
fatality rate of 2.4%, according to WHO. The vast majority of cases and deaths have occurred
in China. For a little perspective, the 2002 SARS outbreak resulted in 8,098 cases and 774 deaths,
so the fatality rate was around 9.6%. And the 2012 MERS outbreak results in 2,494 cases
and 858 deaths, bringing the fatality rate to 34%. Finally, for the 2014 Ebola outbreak,
which was not due to a coronavirus, there were 28,639 cases and 11,316 deaths. The fatality
rate was a whooping 40%!
At a microscopic level, coronaviruses are single strand positive sense RNA viruses with
protein spikes on their surface that look a bit like a crown under a microscope. In
fact, “corona” is latin for crown. Besides looking majestic, these spikes allow the virus
to invade cells lining the respiratory tract and lungs. After binding, the coronavirus
enters and takes over the cellular machinery to make more and more copies of itself so
it can spread to the surrounding cells and get into the mucus.
Sometimes the infection is mild, and some people don't develop any symptoms at all.
For others, they can develop symptoms that can range from mild symptoms like fever, cough,
and shortness of breath, all the way to serious problems like pneumonia. Severe lung damage
can cause acute respiratory distress syndrome, or ARDS, which occurs when the lung inflammation
is so severe that fluid builds up around and within the lungs. The severe infection can
cause septic shock, which happens when the blood pressure falls dramatically and the
body's organs are starved for oxygen. ARDS and shock are the main cause of death for
people with the infection, and this is more likely to occur in those over the age of 60,
smokers, and people with previous medical conditions like hypertension.
In addition to causing disease, coronaviruses can spread quickly. Usually the virus spreads
when people cough or sneeze, and tiny droplets containing the virus are released. These droplets
can land on another person's mouth, nose, or eyes, and that allows the virus to enter
a new person. Virus can also be found in a person's stool, and in rare situations coronavirus
has been transmitted from one apartment to another within a residential building. This
was seen in the 2002 SARS epidemic. At that time, faulty plumbing allowed virus-containing
fecal matter originating from one person's apartment to drift from drainage pipes back
up into fixtures like sinks and toilets within other apartments in the same building. This
created a terrible smell and allowed the virus-containing droplets to deposit on bathroom surfaces,
ultimately causing people in those apartments to get ill. Something similar may have happened
with COVID-19, and this is being actively investigated.
Once a person is infected, symptoms develop an average of 5 days later. This is called
the incubation period. However the incubation period varies from person to person, and in
some studies, the incubation period lasted as long as 24 days! Now there's debate about
whether or not asymptomatic people can spread the disease, because these people typically
have low levels of circulating virus. But even if they do, asymptomatic transmission
likely plays a minor role in the overall epidemic. Viruses are given a reproductive number or
R-naught based on how quickly they spread, and person to person transmission has been
confirmed both in and outside of China. An R naught of 1 means that an infected person
passes it on to 1 new person, an R-naught of 2 means that 1 person spreads it to 2 new
people, and so forth. If the R naught is below 1, the infection peters out, if it's 1 it
stays steady, and if it's above 1, then it continues to spread. The current estimate
for the SARS-CoV-2 R naught is between 2 and 2.5. Of course that's an average, with some
spreading the disease less, and others - called superspreaders - spreading the disease at
a much much higher rate. The exact cause of these superspreaders is unclear, perhaps they
are just in contact with more folks, perhaps their bodies naturally shed more virus, or
perhaps there's some other reason altogether.
To confirm the diagnosis, there should be a real time polymerase chain reaction or rt-PCR
tests, a quick test used in many labs and hospitals that can detect very small amounts
of viral RNA.
Treatment is focused on supportive care - providing fluids, oxygen, and ventilatory support for
really ill people. There's also some early data showing that three medications are highly
effective against SARS-CoV-2 in the laboratory setting. These medications are chloroquine,
an anti-malarial drug; ritonavir, an anti-HIV medication; and remdesivir, an antiviral drug
previously used against Ebola. Remdesivir was given to the first US patient with COVID-19
on day 11 of his illness as he was clinically worsening, and he began to improve the very
next day. Large scale clinical trials using remdesivir are already underway in China.
Unfortunately there's no vaccine currently available to protect against COVID-19. At
best, it looks like a vaccine will be many months away. So the goal is to avoid human
to human transmission, starting with isolating people with COVID-19. Coronaviruses don't
usually spread over long distances in the air, but they can travel roughly 3 feet or
1 meter from one person to another on tiny droplets of saliva, which are produced when
someone's coughing or sneezing. In addition, some strains of coronavirus can survive on
surfaces for over a day. With that in mind, if you're a healthy person living in a non-outbreak
area, the recommendation is to avoid travel to disease outbreak areas, generally stay
away from crowded places, and stay at least 6 feet or 2 meters away from anyone with symptoms.
Wearing a surgical mask is not recommended because the general risk of getting COVID-19
in these settings is so low. As always, careful hand washing is key and it should be done
with soap or alcohol-based hand sanitizers and scrubbing. Also, avoid touching your eyes,
nose, and mouth—this is the area, known as your T-zone is a common entry point for
viruses into the body.
For healthcare workers who are around people with COVID-19, the recommendation is to apply
droplet and contact precautions. That includes wearing personal protective equipment like
a clean, dry surgical mask, gloves, long-sleeved gowns, and eye protection like goggles or
a face shield. When performing a procedure that generates aerosol, like tracheal intubation,
bronchoscopy, CPR, or noninvasive ventilation, it's important to wear a N95 respirator.
This prevents 95% of the small particles, like respiratory droplets, from passing through.
To recap, the SARS-CoV-2 virus causes a respiratory disease called COVID-19. The virus probably
originated from bats, then went to pangolins as an intermediate host, and finally to humans.
The virus travels in respiratory droplets and enters the body via the mouth, nose, or
eyes. Once inside the body, it replicates in the respiratory system, causing symptoms
like fever, cough, and shortness of breath. Some people might develop more dangerous complications
like pneumonia, ARDS, and shock. Treatments are focused on supportive care, but certain
medications like Remdesivir are currently in clinical trials. In the meantime, the best
strategy is prevention -- this includes careful hand washing, avoiding traveling to disease
outbreak areas and crowded places when possible, avoiding touching your T-zone, and if you're
a healthcare worker to use personal protective equipment.


COVID-19 (Coronavirus Disease 19) - causes, symptoms, diagnosis, treatment, pathology

2029 タグ追加 保存
Tina Huang 2020 年 2 月 25 日 に公開
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