THE COVID-19 PANDEMIC A brief essay on transmission, infection, symptoms and treatment

Introduction

December of 2019, in Wuhan, a large metropolitan area inside China's Hubei province, an epidemic of unexplained low respiratory infections seemed to be emerging. On December 31, cases where reported to the WHO country office in China. The first cases were dubbed cases of "pneumonia of unknown etiology.” Soon after , the Chinese Center for Disease Control and Prevention (CDC) conducted a thorough outbreak investigation and eventually discovered that the disease may be attributed to a novel coronavirus belonging to the coronavirus family (CoV) and that it’s most likely origin was the Wuhan seafood market where an animal to human transmission most probably occurred (Cascella, 2020). By January 20, 2020 the first case had reported in the US and on January 30, 2020 the WHO declared the outbreak to be a Public Health Emergency of International Concern (CNN, 2020). Only a few weeks later on February 11, 2020 the WHO Director-General, announced that the disease caused by the virus would be named “COVID-19," as an acronym for “Coronavirus Disease 2019” and at that point the virus has began spreading around the globe as countries began taking their first measures. Additionally it seemed that virus had a more severe impact on elders and people with compromised immune systems, this was worrying as some people rained asymptomatic and continued to spread the virus without knowledge of doing so (Cascella, 2020). At this point, April 19, 2020, around 5 months after the initial reported cases, more than 2 million people around the globe have contracted the novel coronavirus while health care systems are struggling to cope with the huge numbers of patients admitted to hospitals eventually leading to an increased mortality rate (WHO, "COVID-19 situation reports", 2020). The situation is complicated and may be analyzed from many different perspectives and fields as the outbreak has temporarily changed the dynamics of how society operates. This essay will cover the basic biochemical processes involved in the transmission and infection associated with COVID-19 along with symptoms, complications, and treatment.

Transmission and Infection

In order to assess the transmission and virulence factors, whole genomic sequences of the virus where obtained directly through hospitalized patients or from cultures of the virus that where initially obtained from hospitalized patients in Wuhan. It was discovered that the SARS-CoV-2 virus is a betacoronavirus belonging to a new biological group in subgenus COVID-19 REPORT (BIOC1011) "1 Sarbecovirus in the Orthocoronavirinae subfamily. It was also discovered that SARS-CoV-2 shared about 79% of it’s nucleotide sequence with SARS-CoV. it shared 96% nucleotide homology with a SARS-like coronavirus obtained from an Intermediate horseshoe bat. Hence the virus being coined SARS-CoV-2 (Hamid, Mir, & Rohela, 2020). A team from the Berlin Institute of Health (BIH) recently researched how the virus infects cells and which specific cells in the respiratory tract and lung it infects. They discovered that SARS-CoV-2 spike proteins bind to an Angiotensin-converting enzyme 2 (ACE2) receptor on the cell surface (Lukassen, et al., 2020). ACE2 is an enzyme attached to the plasma membrane of cells in the in the lungs, arteries, heart, kidney, and intestines and one of it’s main functions is facilitating the lowering of blood pressure by vasodilation (NCBI, 2020). After binding to ACE2 the spike protein of the virus and the cell membrane fuse in a step crucial for viral infections. This fusing of virus and cell membrane relies on the presence of certain proteases and in the case of SARS-CoV-2 it depends on the serine protease TMPRSS2. Once fused the virus enter the infected cell and it’s genetic code instructs the cell to build more enveloped viruses in a process that basically destroys the infected cell (Belouzard, Chu, & Whittaker, 2009). It should also be noted that the density of ACE2 receptors on cells tends to increase with age and generally seems to be slightly higher in men than in woman, this could potentially explain why the older population seems to be more heavily impacted by COVID-19 and why infections tend to be slightly higher in the male population (Lukassen, et al., 2020). As tend to occur with other respiratory pathogens, including the rhinovirus and influenza viruses, transmission seemed to occur through respiratory droplets from coughing and sneezing. Some researchers believe Aerosol transmission may also occur in cases of exposure within small closed spaces, however more research is required to firmly provide evidence for that hypothesis. Analysis of data of the SARS-CoV-2 outbreak in China seemed to indicate that close contact with an infected individual is necessary for infection. Additionally inspections of data on the outbreak indicated that the average incubation time for the SARS-CoV-2 is 3 to 7 days, however it may also take up to 2 weeks for first symptoms to appear, this is partially why the virus spread so quickly and efficiently. Data of the outbreak in china also showed that the average infected person would theoretically infect 2.2 more people explaining why the number of infected people would double approximately every 7 days (Cascella, 2020).

Signs, Symptoms and Complications

Once infected with SARS-CoV-2 symptoms may start to appear 2-7 days after infection but may also appear as late as 2 weeks after infection leading the disease termed Coronavirus Disease 2019 (COVID-19). The CDC report that was conducted using data from outbreak in Wuhan indicated that the clinical spectrum of COVID-19 is very wide and ranges from paucisymptomatic (mild) cases to clinical conditions where patients must be hospitalized (Huang, et al., 2020). Therefore the authors of the Chinese CDC report divided the manifestations of COVID-19 by severity:

Mild disease:

This severity constitutes 81% of cases and are characterized by non-pneumonia and/or mild pneumonia. These patients usually present with symptoms of an upper respiratory tract viral infection, symptoms include a mild fever, dry cough, sore throat, nasal congestion, headache, malaise, muscle pain. The disease usually subsides within a week to two weeks. 

Severe disease:

This occurred in 14% of cases. Characterized by a respiratory frequency of more than 30/min, and a blood oxygen saturation (SpO2) of less than or equal to 93%, and/or lung infiltrates > 50% within 24 to 48 hours. The symptoms for sever cases range from respiratory symptoms such as cough and shortness of breath that may be present without signs of severe pneumonia to cases involving severe pneumonia which may often lead to complications. In severe cases of pneumonia symptoms included a Fever associated with severe dyspnea, respiratory distress, tachypnea, and hypoxia.

Critical disease (Complications):

Constitute 5% of cases. Cases were characterized by respiratory failure, septic shock, and/or multiple organ dysfunction (MOD) or multiple organ failure (MOF). The most common type of complication to occur is acute respiratory syndrome (ARDS) which may further classified by severity into mild, moderate and severe ARDS. If a person is diagnosed with ARDS a clinician must asses if the patient should be put on ventilator based on a set of criteria the asses respiratory function. If the state of ARDS persists there is very high probability that the patient might succumb to complete respiratory failure.

Sepsis:

In some cases, although rare, a person might enter sepsis or septic shock, a life threatening dysfunction of the bodies organs, caused by an unregulated immune response from the host. In the case of COVID-19 the cases of septic shock seem to be very serious and are characterize by a diverse range of signs and symptoms including, but not limited to, severe hypoxemia, tachycardia, altered mental state, thrombocytopenia and functional altercations of organs. In severe cases if symptoms persist the patient may die (Cascella, 2020).

Management of Symptoms and Treatment

Currently treatment for COVID-19 relies mainly on managing the occurring symptoms in patients. There is currently no specific antiviral developed for the treatment of COVID-19. For patents with a severe infection the main intervention is oxygen therapy and if respiratory failure occurs patients might need mechanical ventilation, while if a patient begins to succumb to septic, hemodynamic support is essential to improve oxygenation (Hui, et al., 2019).

Conclusion

The COVID-19 pandemic is surely shocking and the sheer speed at which the SARSCoV- 2 spread is alarming. Although the majority of COVID-19 cases are considered to be mild, the efficient transmission of the virus along with it’s long incubation period may lead to very large number of increasing infections within a very short time frame, this may strain the healthcare systems and if the number of severe cases surpasses a healthcare system’s carrying capacity the effects can be devastating, and ultimately lead to a high mortality rate. Therefore, for now, isolation and preventive measures seem to be the most impactful way of slowing down the infection rate and decreasing the strain on healthcare systems until a vaccine or antiviral medication specifically for COVID-19 is available. Much of the information in this essay should be assessed critically as research on the SARS-CoV-2 and COVID-19 is still in it’s very early phases and a lot of research still has not been published. The work referenced in this essay should also be continuously checked for any updates and edits as these may occur on a daily basis. However, the fast and efficient work done by researchers and healthcare workers must be acknowledged as this pandemic demonstrates the importance of the biomedical sciences in the progress, survival and well being of us as a species.

References:

ACE2 angiotensin I converting enzyme 2 [Homo sapiens (human)] - Gene - NCBI. (2020, April 20). Retrieved April 21, 2020, from https://www.ncbi.nlm.nih.gov/gene/59272

Belouzard, S., Chu, V. C., & Whittaker, G. R. (2009, April 7). Activation of the SARS coronavirus spike protein via sequential proteolytic cleavage at two distinct sites. Retrieved April 21, 2020, from https://www.pnas.org/content/106/14/5871.long

Cascella, M. (2020, April 6). Features, Evaluation and Treatment Coronavirus (COVID-19). Retrieved April 19, 2020, from https://www.ncbi.nlm.nih.gov/books/NBK554776/

Coronavirus Outbreak Timeline Fast Facts. (2020, April 16). Retrieved April 19, 2020, from https://edition.cnn.com/2020/02/06/health/wuhan-coronavirus-timeline-fast-facts/index.html

COVID-19 situation reports. (2020, April 18). Retrieved April 19, 2020, from https://www.who.int/emergencies/diseases/novel-coronavirus-2019/situation-reports

Mackenzie, J. S., & Smith, D. W. (2020). COVID-19: a novel zoonotic disease caused by a coronavirus from China: what we know and what we don't. Microbiology Australia, MA20013. Advance online publication. https://doi.org/10.1071/MA20013

Lukassen, S., Chua, R. L., Trefzer, T., Kahn, N. C., Schneider, M. A., Muley, T., … Eils, R.

(2020, April 17). SARS-CoV-2 receptor ACE2 and TMPRSS2 are primarily expressed in bronchial transient secretory cells. Retrieved April 21, 2020, from https://www.embopress.org/doi/10.15252/embj.20105114

Hamid, S., Mir, M. Y., & Rohela, G. K. (2020, April 14). Novel coronavirus disease (COVID-19): a pandemic (epidemiology, pathogenesis and potential therapeutics). Retrieved April 21, 2020, from https://www.sciencedirect.com/science/article/pii/S2052297520300317 Huang, C., Wang, Y., Li, X., Ren, L., Zhao, J., Hu, Y., Zhang, L., Fan, G., Xu, J., Gu, X., Cheng, Z., Yu, T., Xia, J., Wei, Y., Wu, W., Xie, X., Yin, W., Li, H., Liu, M., Xiao, Y., … Cao, (2020). Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet (London, England), 395(10223), 497–506. https://doi.org/10.1016/S0140-6736(20)30183-5 Hui, D. S., Chow, B. K., Lo, T., Tsang, O. T. Y., Ko, F. W., Ng, S. S., … Chan, M. T. V. (2019, April 11).

Exhaled air dispersion during high-flow nasal cannula therapy versus CPAP via different masks. Retrieved April 22, 2020, from https://www.ncbi.nlm.nih.gov/pubmed/30705129