SARS-Covid-19
​SARS-Covid-19
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single-stranded RNA virus
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Spike, membrane, and envelope surface viral proteins of coronavirus are embedded in host membrane-derived lipid bilayer encapsulating the helical nucleocapsid comprising viral RNA
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Histopathological investigation of tissues from SARS-CoV-2 infected patients showed virus-induced cytopathic effect with signs of acute respiratory distress syndrome in lung cells.
Figure X. Kumar, S., Nyodu, R., Maurya, V. and Saxena, S., 2020. Morphology, Genome Organization, Replication, and Pathogenesis of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Medical Virology: From Pathogenesis to Disease Control, pp.23-31.
Pathology
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The virus initially binds to its target cell via the spike protein binding to the ACE2 receptor (present on cells in the respiratory system), followed by other co-receptors.
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This causes the virus to be taken into the cell by Endocytosis.
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The next step in viral replication and infection of the cell is the mRNA from the virus to be released from the virus into the cell and delivered to the ribosome (where the RNA is translated into a proteins)
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the first step in the virus replicating itself to make the spike proteins and other proteins such as the Nucleocapsid, membrane, envelope and accessory proteins.
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As well as to replicate the viruses own genetic material.
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Due to the Coronavirus being an enveloped virus. All the proteins that are located on the virus’s outer envelope are transported to the endoplasmic reticulum (ER)
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Which then assessable on the ER membrane which then forms an ER-Golgi intermediate complex (the start of forming the envelope of the virus (the coating of the virus).
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While this process is occurring the viral (RNA) genome is combined with the nucleocapsid to form a complete nucleocapsid which is stored in virus core.
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This is then combined with the ER- Golgi intermediate complex to form a whole viral particle this is then released from the cell by Exocytosis to go on and infect another cell and repeat this process many times over.
Figure Y. Cevik, M., Kuppalli, K., Kindrachuk, J. and Peiris, M., 2020. Virology, transmission, and pathogenesis of SARS-CoV-2. BMJ, p.m3862.
​Progression of COVID-19 infection in terms of the amount of virus particles and illness
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There is a 5-day incubation period. Where the number of viral particles increase very quickly up until around day 1 of the onset of symptoms, with the number of viral particles decreasing after day 3 of the onset of symptoms.
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The mild illness starts at day 1 increasing to a peak in symptoms around day 5 and then improving to the absence of symptoms around day 10.
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If the illness becomes severe or critical the symptoms do not improve after the 5th day mark but will continue to get worse.
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Progressing to the patient needing to be hospitalised.
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On average by day 8 if the infection continues to get worse, they start developing shortness of breath. Which may lead to acute respiratory distress syndrome.
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This is a type of respiratory failure caused by the onset of rapid inflammation in the lungs, this needs to be treated by giving supplementary oxygen.
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If the disease continues to decline, then It could reach the critical illness stage needing ITU admission and ventilation to support the respiratory system to supply oxygen to the patient’s lung.
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The antibody response starts late 2nd day of the onset of symptoms and gradually increases.
Figure Z..Cevik, M., Kuppalli, K., Kindrachuk, J. and Peiris, M., 2020. Virology, transmission, and pathogenesis of SARS-CoV-2. BMJ, p.m3862.