Corona virus

1. 1
CORONAVIRUS
Introduction of coronavirus
coronaviruses are a group of related rna viruses that cause diseases in mammals and birds. In
humans, these viruses cause respiratory tract infections that can range from mild to lethal. Mild illnesses
include some cases of the common cold (which is also caused by other viruses, predominantly rhinoviruses),
while more lethal varieties can cause SARS, mers, and COVID-19.the name "coronavirus" is derived from
latin corona, meaning "crown" or "wreath", itself a borrowing from greek korṓnē, "garland, and wreath".
The name was coined by june almeida and david tyrrell who first observed and studied human
coronaviruses. The word was first used in print in 1968 by an informal group of virologists in the journal
nature to designate the new family of viruses.
Virus classification:
(unranked) virus
Realm riboviria
Kingdom orthornavirae
Phylum pisuviricota
Class pisoniviricetes
Order nidovirales
Family coronaviridae
Sub family orthocoronavirinae
Genera alpha coronavirus (type species: alphacoronavirus 1)
beta coronavirus (type species murine coronavirus)
gama coronavirus (type species avian coronavirus)
deltacoronavirus (type species bulbul coronavirus)
Structure
coronaviruses are large, roughly spherical, particles with bulbous surface projections.
Diameter of virus
 The average diameter of the virus particles is around 125 nm.
 The diameter of the envelope is 85 nm and the spikes are 20 nm long.
The envelope of the virus in electron micrographs appears as a distinct pair of electron-dense shells (shells
that are relatively opaque to the electron beam used to scan the virus particle). The viral envelope consists of
a lipid bilayer, in which the membrane (m), envelope (e) and spike (s) structural proteins are anchored. The
ratio of e:s:m in the lipid bilayer is approximately 1:20:300.
 On average a coronavirus particle has 74 surface spikes. Subsets of coronaviruses (specifically
the members of beta coronavirus subgroup a) also have a shorter spike-like surface protein called
hem agglutinin esterase (he).

2. 2
fig: structure of coronavirus.
Genome
coronaviruses contain a positive-sense, single-stranded rna genome. The genome size for
coronaviruses ranges from 26.4 to 31.7 kilobases. The genome size is one of the largest among rna viruses.
The genome has a 5′ methylated cap and a 3′ polyadenylated tail.
Replication cycle
1. Cell entry
infection begins when the viral spike protein attaches to its complementary host cell receptor.
After attachment, a protease of the host cell cleaves and activates the receptor-attached spike protein.
Depending on the host cell protease available, cleavage and activation allows the virusto enter the
host cell by endocytosis or direct fusion of the viral envelop with the host membrane.
2. Genome translation
 On entry into the host cell, the virus particle is uncoated, and its genome enters the cell
cytoplasm.
 The coronavirus rna genome has a 5′ methylated cap and a 3′ polyadenylated tail, which allows
the rna to attach to the host cell's ribosome for translation.
 The host ribosome translates the initial overlapping open reading frames orf1a and orf1b of the
virus genome into two large overlapping polyproteins, pp1a and pp1ab.
 The larger polyprotein pp1ab is a result of a -1 ribosomal frame shift caused by a slippery
sequence (uuuaaac) and a downstream rna pseudo knot at the end of open reading frame orf1a.
The ribosomal frame shift allows for the continuous translation of orf1a followed by orf1b.
 The polyproteins have their own proteases, plpro and 3clpro, which cleave the polyproteins at
different specific sites.

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 The cleavage of polyprotein pp1ab yields 16 nonstructural proteins. Product proteins include
various replication proteins such as rna-dependent rna polymerase, rna helicase, and
exoribonuclease.
3. Replicase-transcriptase
a number of the nonstructural proteins coalesce to form a multi-protein replicase-transcriptase
complex. The main replicase-transcriptase protein is the rna-dependent rna polymerase. It is directly
involved in the replication and transcription of rna from an rna strand. The other nonstructural
proteins in the complex assist in the replication and transcription process.
The exoribonuclease nonstructural protein, for instance, provides extra fidelity to replication by
providing a proofreading function which the rna-dependent rna polymerase lacks.
 The replicase-transcriptase complex is also capable of genetic recombination when at least two viral
genomes are present in the same infected cell. Rna recombination appears to be a major driving force
in determining genetic variability within a coronavirus species, the capability of a coronavirus
species to jump from one host to another and, infrequently, in determining the emergence of novel
coronaviruses. The exact mechanism of recombination in coronaviruses is unclear.
4. Assembly and release
the replicated positive-sense genomic rna becomes the genome of the progeny viruses. The
mrnas are gene transcripts of the last third of the virus genome after the initial overlapping reading
frame. These mrnas are translated by the host's ribosomes into the structural proteins and a number
of accessory proteins. Rna translation occurs inside the endoplasmic reticulum. The viral structural
proteins s, e, and m move along the secretory pathway into the golgi intermediate compartment.
There, the m proteins direct most protein-protein interactions required for assembly of viruses
following its binding to the nucleocapsid. Progeny viruses are then released from the host cell
by exocytosis through secretory vesicles. Once released the viruses can infect other host cells
How does this virus spread?
with cases of the new coronavirus reported, health officials are focused on slowing the spread. By
understanding how coronavirus spreads, you can take the right steps so you don't get sick and infect others.
Person-to-person transmission
Experts believe the virus that causes COVID-19 spreads mainly from person to person. There are several
ways this can happen:
 Droplets. When an infected person coughs, sneezes, or talks, droplets with the virus fly into the air
from their nose or mouth. Anyone who is within 6 feet of that person can breathe those droplets into
their lungs.

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 Aerosolized transmission. Research shows that the virus can live in the air for up to 3 hours. When
you breathe air that has the virus floating in it, it gets into your lungs.
 Surface transmission. Another way to catch the new coronavirus is when you touch surfaces that
someone who has the virus has coughed or sneezed on. You may touch a countertop or doorknob
that's contaminated and then touch your nose, mouth, or eyes. The virus can live on surfaces like
plastic and stainless steel for 2 to 3 days. To stop it, clean and disinfect all counters, knobs, and other
surfaces you and your family touch several times a day.
COVID 19
COVID-19 appeared in wuhan, a city in china, in december 2019. Although health officials are still
tracing the exact source of this new coronavirus, early hypotheses thought it may be linked to a seafood
market in wuhan, china. Some people who visited the market developed viral pneumonia caused by the new
coronavirus. A study that came out on jan. 25, 2020, notes that the individual with the first reported case
became ill on dec. 1, 2019, and had no link to the seafood market. Investigations are ongoing as to how this
virus originated and spread.
Incubation period for COVID-19
it appears that symptoms are showing up in people within 14 days of exposure to the virus.
Symptoms of COVID-19
COVID-19 symptoms include:
 Cough
 Fever
 Shortness of breath
 Muscle aches
 Sore throat
 Unexplained loss of taste or smell
 Diarrhea
 Headache
In rare cases, COVID-19 can lead to severe respiratory problems, kidney failure or death.
Diagnosis and treatment
 Diagnosis
If you develop symptoms of coronavirus disease 2019 (COVID-19) and you've been exposed
to the virus, contact your doctor. Tell him or her if you've traveled to any areas with ongoing
community spread of COVID-19 according to CDC and WHO. Also let your doctor know if you've
had close contact with anyone who has been diagnosed with COVID-19. Factors used to decide
whether to test you for COVID-19 may differ depending on where you live. Depending on your

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location, you may need to be screened by your clinic to determine if testing is appropriate and
available.
 Treatment
Currently, no medication is recommended to treat COVID-19, and no cure is available.
Antibiotics aren't effective against viral infections such as COVID-19. Researchers are testing a
variety of possible treatments. The FDA granted permission for some medications approved for other
diseases to be used to treat severe COVID-19 when no other options are available. Two malaria
drugs — hydroxychloroquine and chloroquine — and an antiviral drug, remdesivir, have been
approved for this use.treatment is directed at relieving symptoms and may include:
 Pain relievers (ibuprofen or acetaminophen)
 Cough syrup or medication
 Rest
 Fluid intake
There is no evidence that ibuprofen or other nonsteroidal anti-inflammatory drugs need to be
avoided. If you have mild symptoms, your doctor may recommend that you recover at home. He or
she may give you special instructions to monitor your symptoms and to avoid spreading the illness to
others. You'll likely be asked to isolate yourself as much as possible from family and pets while
you're sick, wear a mask when you're around people and pets, and use a separate bedroom and
bathroom.
Your doctor will likely recommend that you stay in home isolation for a period of time except to get
medical care. Your doctor will likely follow up with you regularly. Follow guidelines from your
doctor and local health department about when you can end home isolation.
If you're very ill, you may need to be treated in the hospital.
Is this coronavirus different from SARS?
SARS stands for severe acute respiratory syndrome. In 2003, an outbreak of SARS started in china
and spread to other countries before ending in 2004. The virus that causes COVID-19 is similar to the one
that caused the 2003 SARS outbreak: both are types of coronaviruses. Much is still unknown, but COVID-
19 seems to spread faster than the 2003 SARS and also may cause less severe symptoms.

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Coronavirus prevention:
You can reduce your chances of being infected or spreading COVID-19 by taking some simple precautions:
 Regularly and thoroughly clean your hands with an alcohol-based hand rub or wash them with soap
and water. Because washing your hands with soap and water or using alcohol-based hand rub kills
viruses that may be on your hands.
 Maintain at least 1 meter (3 feet) distance between yourself and others. Becausewhen someone
coughs, sneezes, or speaks they spray small liquid droplets from their nose or mouth which may
contain virus. If you are too close, you can breathe in the droplets, including the COVID-19 virus if
the person has the disease.
 Avoid going to crowded places. Because where people come together in crowds, you are more likely
to come into close contact with someone that has coivd-19 and it is more difficult to maintain
physical distance of 1 meter (3 feet).
 Avoid touching eyes, nose and mouth. Because hands touch many surfaces and can pick up viruses.
Once contaminated, hands can transfer the virus to your eyes, nose or mouth. From there, the virus
can enter your body and infect you.
 Make sure you, and the people around you, follow good respiratory hygiene. This means covering
your mouth and nose with your bent elbow or tissue when you cough or sneeze. Then dispose of the
used tissue immediately and wash your hands. Because droplets spread virus. By following good
respiratory hygiene, you protect the people around you from viruses such as cold, flu and COVID-
19.
 Stay home and self-isolate even with minor symptoms such as cough, headache, mild fever, until you
recover. Have someone bring you supplies. If you need to leave your house, wear a mask to avoid
infecting others. Becauseavoiding contact with others will protect them from possible COVID-19
and other viruses.
 If you have a fever, cough and difficulty breathing, seek medical attention, but call by telephone in
advance if possible and follow the directions of your local health authority. Because national and
local authorities will have the most up to date information on the situation in your area. Calling in
advance will allow your health care provider to quickly direct you to the right health facility. This
will also protect you and help prevent spread of viruses and other infections.
 Keep up to date on the latest information from trusted sources, such as who or your local and
national health authorities. Because local and national authorities are best placed to advise on what
people in your area should be doing to protect themselves.