Essay on How Does Covid 19 Spread

COVID 19 The Pandemic

Severity of pandemics COVID 19 and MERS COV

As the world is witnessing the epidemic of COVID 19 a disease caused by the novel coronavirus (SARS-COV 2), as per the genetic and clinical evidence COVID-19 shows similarity to the previous pandemics that SARS-COV (2002) and MERS-COV (2011). The first case of COVID-19 was noticed in Wuhan, Hubei province, China, and MERS COV in Jeddah Saudi Arabia. All these viruses are of zoonotic origin. That means this virus has been transferred from animals that bats. Here we will be comparing even the severity of the epidemic COVID-19 and MERS COV. COVID-19 is more severe when compared with pandemics like MERS COV.

Viral shedding and Innate immune responses

COVID-19 has approximately 50% similarity when compared with MERS-COV (Middle East Respiratory Syndrome) according to the genome sequencing. And they belong to the beta coronavirus family. Both viruses are respiratory-related illnesses.

COVID-19 uses angiotensin-converting enzyme 2(ACE 2) as its main cellular receptor, which is broadly expressed in vascular endothelium, respiratory epithelium, alveolar monocytes, and macrophages.1 As all these are related to either heart or respiratory system or the immune system. The cellular receptor of MERS COV is dipeptidyl peptidase. The putative receptor of COVID-19, ACE2 is mainly expressed in a small subset of cells in the lung called type 2 alveolar cells. MERS COV infects the type I interferon Aerosolized uptake of COVID-19 leads to infection ACE 2 expressing target cells such as alveolar type 2 or other unknown target cells. The virus may decrease anti-viral interferon responses resulting in uncontrolled viral shedding. The stream of neutrophils and macrophages results in the hyper-production of pro-inflammatory cytokines. This situation is called a ‘cytokine storm.’ There are possibilities that COVID-19 can produce antibodies.2 As ACE 2 is expressed minimally in potential target immune cells.

In the case of MERS COV, there is also an inflow of high inflammatory neutrophils and monocytes-macrophages help in destroying the infected cells. But in the case of COVID 19 immune interference varies when compared with MERS COV. In the case of COVIID 19 transmission of the virus is reported to cover even asymptomatic individuals. This can be the reason for the delayed response of innate immune response.2 Innate immune response is a critical factor for diseases outcome.

Transmission

COVID-19 and MERS COV has similar symptoms. The most common symptoms are fever, fatigue and respiratory symptoms are cough, sore throat, and shortness of breath.

It is said that the natural reservoir of viruses is bats but there is an intermediate host between bats and human that is possibly camel in case of MERS COV and in case of COVID-19 is possibly Pangolin (as per the reports of February 7, 2020), the genetic characteristics had 99% similarity. Few cases had links with the seafood market, but few had no contact with it, and few how have not even visited China. This concludes that this virus can get transmitted to human beings. And this is the same in the case of MERS COV, the virus is transmitted between human beings. The primary mode of infection among human beings is through close contact, which is by spraying droplets from infected persons through coughing or sneezing.

COVID-19 is highly contagious because of asymptomatic and pre-symptomatic cases. In order to find the increase in infected individuals in the near future pathogens. There is a mathematical model that is to calculate the basic reproduction, R0, which is the average number of people one infected individual will pass the virus on to. The R0 of COVID-19 is between 2.2-2.6 and of MERS COV is less than 1. If the R0 is greater than one 1, the virus can be transmitted for a longer period. COVID-19 has an R0 between 2.2-2.6, with an epidemic doubling time is 6.4 days but MERS COV has higher doubling time. This also means that on average each infected individual has the possibility of transmitting the virus to 2.2 other individuals.2 For this reason, there has been a rapid spread of COVID-19 when compared with MERS COV.

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Case fatality rate

The case fatality rate, in epidemiology, is the proportion of people who die from a specific disease among all individuals diagnosed with the disease from a certain period. It's beneficial to determine the disease severity and the outcome of the disease. A higher percentage of CFR means poor outcomes. This is also used to see the effect of new vaccines or treatments on the infected individuals.

The CFR is not constant, there will be a possibility of varying in the CFR based on the infected number of individuals, treatment, change in time, and even the immune of the patients.

CFR formula, once the pandemic is ended, is,

• Case Fatality Rate= [deaths / infected individuals] * 100

But the case of COVID-19 is still going on. So, using the above formula will not represent the true case fatality rate. There is a separate formula for CFR of ongoing pandemic mentioned in the American Journal of Epidemiology study. That is,

• Case Fatality Rate= [deaths / (death + recovered)] * 100
• COVID-19: - CFR = [270,124/ (270124 + 1,335,111)] * 100 = 16.8277% ~ 17% (May 07, 2020, 22:29 GMT)
• MERS COV: - CFR = [858 / 2494] * 100 = 34.4026% ~ 34%

As we can clearly see that CFR of MERS COV is higher than COVID-19. This means that MERS COV is more severe than COVID-19. MERS COV had poor outcomes as its CFR is comparatively higher.

And it also said that the CFR of COVID-19 can still be lower, as there are asymptomatic cases of COVID-19. That means there are still infected individuals who did not show symptoms of COVID-19 or had mild symptoms but did not get hospitalized. They had just quarantined themselves and got recovered from the disease. That means there is an increase in the value of the denominator, which leads to a decrease in the CFR of COVID-19.

In a nutshell

Even though the incubation period for COVID-19 is around 14, MERS COV also has an incubation period in the same range. But the highest incubation period for COVID-19 is 24 days which is dangerous. And in the case of COVID-19, there are many asymptomatic cases, it is estimated that the transmission during the asymptomatic period is approximately 5%. The virus can be airborne for 3 hours and globalization also place a role in transmitting the virus faster when compared with MERS COV. As per pathophysiology, the influx of neutrophils and macrophages can help in producing antibodies but there are possibilities that they can destroy the other cells like type 1 and type 2 cells in the alveolar. That will lead to the collapse of the alveolar. In severe cases, the patient will develop other diseases like pneumonia, kidney failure, respiratory syndrome, and even death. All the factors lead towards the direction that, COVID-19 is more contagious.

Reference

1. (2019, November). Retrieved May 2020, from World Health Organization: https://www.who.int/emergencies/mers-cov/en/
2. Cao, W., & Li, T. (2020). COVID-19: towards the understanding of pathogenesis. Cell Research, 1-3.
3. de Groot, R. J., Baker, S. C., Baric, R. S., Brown, C. S., Drosten, C., Enjuanes, L., ... & Perlman, S. (2013). Commentary: Middle East respiratory syndrome coronavirus (MERS-CoV): announcement of the Coronavirus Study Group. Journal of virology, 87(14), 7790-7792.
4. Harrington, R. A. (2020, May 05). Retrieved May 07, 2020, from Encyclopaedia Britannica: https://www.britannica.com/science/case-fatality-rate
5. Prompetchara, E., Ketley, C., & Palaga, T. (2020). Immune responses in COVID-19 and potential vaccines: Lessons learned from SARS and MERS epidemic. Asian Pac J Allergy Immunol, 38(1), 1-9.
6. (n.d.). Retrieved May 07, 2020, from Worldometers: https://www.worldometers.info/coronavirus/coronavirus-death-rate/
7. Ninja Nerd Science. (2020, March 16). COVID-19 | Coronavirus: Epidemiology, Pathophysiology, Diagnostics. Retrieved from: https://www.youtube.com/watch?v=PWzbArPgo-o