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Coronavirus description and transmission

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Coronavirus description and transmission

Introduction

 

The video describes the evolution of the novel coronavirus based on other familiar and well understood viral illnesses that are similar to it. They include the common cold, severe acute respiratory syndrome (SARS), and Middle Eastern respiratory syndrome MERS. From these comparisons and existing data on COVID-19, one can make various deductions on the characteristics of the virus (Campbell, 2020).

 

Coronavirus description and transmission

The video uses a viral disease graph that describes infectious diseases and their evolution in general to explain COVID-19. The first confirmed case was on December 1, 2019, and by February, the WHO announced it as an epidemic of global concerns. Currently, the disease is in over 200 countries, with over 4 million cases and 300,000 deaths (Worldometer, 2020). However, it is thought to be less virulent, less lethal (with a less severe clinical appearance) than SARS and MERS, which means it can spread more easily (Petrosillo, Viceconte, Ergonul, Ippolito, & Petersen, 2020). The video illustrates disease evolution as a bell curve of symptomatic illness with a severity-time axis. The point of infection where exposure to the virus (etiological organism) occurs, thus introducing it to the body and resulting in the disease (Campbell, 2020).

 

The novel coronavirus is a respiratory virus whose human-to-human transmission is thought to occur through respiratory droplets transferred from an infected person’s cough or sneeze. The virus travels in the air through these droplets, whereby another person in close contact with the infected person can inhale them. It has also been found to persist on surfaces  (Harapan et al., 2020). Therefore, transmission can also occur when one touches an infected surface and transfers it to their mucous membrane.

 

Survival in cells, reproduction, and infection

 

The coronavirus enters the respiratory system and goes down into the lower airways (bronchi, bronchioles, alveoli), where the viral particles (virions) invade the cells. These viruses are obligate

intracellular parasites that can only live inside host cells. Reproduction or viral replication occurs when the virion hijacks the cell’s ability to produce proteins, forcing it instead to produce the virion’s proteins. The process is similar in such respiratory infections caused by RNA viruses. It begins with attachment and membrane fusion between the virion and the host cell, then releases of the viral RNA genome into the cytoplasm. It enters the nucleus where replication takes place. Then the genomic RNA exits back into the cytoplasm for assembly and coating by the envelope glycoproteins and nucleocapsid proteins. The process produces multiple virion-containing vesicles, which bud from the plasma membrane, spreading and infecting other cells throughout the lungs in a similar fashion (Yi, Lagniton, Ye, Li, & Xu, 2020).

 

Coronavirus can be classified as a droplet infection. Its movement from person-to-person involves shedding of virion particles from the respiratory epithelial cells into the mucus on the surface. From here, the infected person can cough, sneeze, spit, or breathe them out through the moisture droplets coming from the respiratory system’s mucous lining. Then another person can inhale them directly or get them from contact with a contaminated surface. The viral numbers continue to increase from the point of infection. This point is outside the symptomatic bell curve, which means that the virus exists, is multiplying, and could spread even when one is feeling okay and not showing any signs of illness (incubation period). Coronavirus thus exhibits infection and transmission in the pre-symptomatic or incubation stage. This characteristic is one of the significant risk factors contributing to the virus’s massive spread (ECDC, 2020; Campbell, 2020).

 

A study from the first cases estimates that the incubation period lasts between 1-14 days, often occurring for 3-7 days (Yi, Lagniton, Ye, Li, & Xu, 2020). Most countries are enforcing a 14-day isolation (quarantine) period for people thought to be infected, based on this incubation period.  As the virus increases, it begins to affect the body. Before the symptomatic period, and after incubation, the infected person may experience the prodromal phase, which is a period that presents with general signs and symptoms not indicative of any particular illness (Lumen Microbiology, 2020). Then the person becomes symptomatic due to the toxins and damages the virus causes during the period of illness shown by the bell curve peak (Campbell, 2020).

 

Immune response

 

Meanwhile, the body tries to protect itself and fight off the virus through the immune system. There is currently no immunity for COVID-19 in the human population, making everyone susceptible to the infection. The immune response is supposedly similar to other coronaviruses. When the virus invades, the host’s immune system recognizes it as a foreign body or antigen through pattern recognition receptors (PRRs). The virus activates various pathways and reactions in the body that limit its increase, spread, and damage. Some immune responses are immediate, and others are recruited or join later on. For instance, when the SARS-CoV virus escapes immune responses, the body engages the white blood cells and adaptive immunity (Yi, Lagniton, Ye, Li, & Xu, 2020). The lymphocytes recognize the foreign epitope, and they manufacture antibodies.

 

As the antibody synthesis process continues, they become more specific for the antigen and get better at combating it. Some cells kill the virus-infected cells, and others continue to defend cells that have not been attacked. The body develops specific acquired immunity when it generates particular antibodies to combat a particular infection. As the antibodies increase together with the viruses during the illness period until they are enough to overpower the disease. When they start killing the viral cells faster than they can reproduce, the patient begins to recover. The number of antibodies continues to increase for some time even after the symptomatic period is over. Even when they stop, the antibodies remain in the body for another period. They leave a residual population of memory cells that can remember the antigen. In case the virus attacks again, memory lymphocytes cause faster antibody synthesis, thus developing immunity (Campbell, 2020; Yi, Lagniton, Ye, Li, & Xu, 2020).

 

Symptoms, effects, and risks

 

The COVID-19 coronavirus is chemically different from other coronaviruses like those of MERS and SARS, so immunity acquired for the two cannot work against this novel COVID-19 coronavirus. The final stages of infection may involve a sequela, which is a period of aftereffects, such as post-viral fatigue that one may encounter after the body resolves the infection. The virus has a wide distribution of levels of severity. The most prevalent symptom during illness is fever, which appears in most patients at the onset of the disease. Other common symptoms may accompany the fever, including coughing and fatigue. Less common symptoms are shortness of breath, dizziness, headaches, chest pain, diarrhea, and nausea. Some patients may present with dyspnea and hypoxemia a week after disease onset. In severe cases, patients may develop acute respiratory syndrome, coagulopathy, metabolic acidosis, and septic shock. A few could also have cardiac complications such as cardiac injury afterward. The disease may also affect lung functions, and vulnerable patients would require a high flow of oxygen from ventilators to assist in respiration. The lung complications and lack of oxygen could lead to death. On the other hand, some people hardly present with any symptoms (Campbell, 2020).

 

Conclusion

 

The COVID-19 broke out in Wuhan, China, and has now infected millions of people worldwide and caused multiple deaths and other catastrophic effects. It is caused by severe acute respiratory syndrome (SARS) coronavirus 2 (SARS-CoV-2). Since it is related to the SARS coronavirus, which caused SARS, and other coronaviruses, it is thought to have similar transmission mechanisms and symptoms.  (Yi, Lagniton, Ye, Li, & Xu, 2020). This report summarizes the deductions of what this virus is and how it works, as explained in the video cited herein.

 

References

 

Campbell, J. (2020, January 30). Coronavirus, Disease evolution. UK: YouTube. Retrieved from https://www.youtube.com/watch?v=xotNiLJDT-c

ECDC. (2020). Coronavirus disease 2019 (COVID-19) pandemic: increased transmission in the EU/EEA and the UK- Seventh update. Stockholm: European Centre for Disease Prevention and Control.

Harapan, H., Itohd, N., Yufika, A., Winardif, W., Keam, S., Te, H., . . . Mudatsir, M. (2020). Coronavirus disease 2019 (COVID-19): A literature review. Journal of Infection and Public Health, 667-673. doi:https://doi.org/10.1016/j.jiph.2020.03.019

Lumen Microbiology. (2020). Characteristics of Infectious Disease. Retrieved from Microbial Mechanisms of Pathogenicity: https://courses.lumenlearning.com/microbial/chapter/characteristics-of-infectious-disease/

Petrosillo, N., Viceconte, G., Ergonul, O., Ippolito, G., & Petersen, E. (2020). COVID-19, SARS, and MERS: are they closely related? Clinical Microbiology and Infection, 1-6. doi:doi.org/10.1016/j.cmi.2020.03.026

Worldometer. (2020, May 18). COVID-19 CORONAVIRUS PANDEMIC. Retrieved from Worldometer: https://www.worldometers.info/coronavirus/?utm_campaign=homeAdUOA?Si

Yi, Y., Lagniton, P. N., Ye, S., Li, E., & Xu, R.-H. (2020). COVID-19: what has been learned and to be learned about the novel coronavirus disease. International Journal of Biological Sciences, 1753- 1766. doi:10.7150/ijbs.45134

 

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