SARS-CoV-2 Background

Unless you’ve been on a meditation retreat for the last 2 months, you’ve heard of “COVID-19”, coronavirus, SARS-CoV-2 or the Rona as the Aussie’s say, but perhaps you still have questions. We are here to help. Here we review the SARS-CoV-2 pathogen which causes the disease COVID-19.

SARS-CoV-2 is a novel coronavirus that emerged in the city of Wuhan in Hubei Province, China in 2019. It is a member of the coronavirus family which includes other coronaviruses that have circulated in human populations for a long time and produce mild respiratory infections like the common cold. Two other coronaviruses emerged from animals (from bats and then bridging hosts) to humans in the past two decades: SARS-CoV-1 (known as SARS-Severe Acute Respiratory Syndrome Coronavirus 1) and MERS CoV (Middle East Respiratory Syndrome Coronavirus). SARS-CoV-2, Like its close viral ‘relatives’, uses a specific cell receptor to invade cells in our lungs and GI (gastrointestinal) tract, thus causing the disease known as COVID-19. Although some sources vary, most studies agree on a mean incubation period (the time period from when you are exposed to the virus until you start to experience symptoms) of about 5 days, with some people experiencing symptoms as few as 2 days after exposure and others as many as >14 days after exposure. Some infected people may experience very few symptoms or no symptoms at all (more on this later)! Since this virus invades our lower respiratory system, symptoms for COVID-19 mostly involve respiratory signs including a dry cough (cough that does not produce very much or no mucus) and difficulty breathing/shortness of breath. The GI tract infection can lead to diarrhea, nausea, vomiting, and loss of appetite, but these are not as common as respiratory symptoms. These infections cause our bodies to mount an immune response to kill virus-infected cells and limit spread and damage. This immune response results in the fever and fatigue associated with COVID-19 and may lead to further complications. Even after our immune system has cleared the virus, we could experience complications like secondary infections with pneumonia-causing bacteria.  

There are some key concepts to know about SARS-CoV-2 and COVID-19 vs the other coronaviruses we have seen before:

  • Although the fatality rate (number of people who die when infected with the virus) is relatively low compared to SARS-CoV-1, the infection rate is much much higher and so the virus spreads quickly
  • Unlike SARS-CoV-1 and MERS, many people infected with SARS-CoV-2 are likely to experience either mild symptoms or no symptoms at all, making the jobs of public health workers even harder because it is difficult to tell if someone is infected without testing.
    https://doi.org/10.1016/S1473-3099(20)30129-8

We will discuss some of these ideas at length later, but we hope that you understand enough about the basics of the SARS-CoV-2 coronavirus and the COVID-19 disease it causes so you feel prepared to read our later content.

Origins

The pathogen responsible for COVID-19, SARS-CoV-2, emerged in Wuhan, China, in late 2019. The virus is thought to have originated in a bat before it successfully infected what we call an intermediate host, and then finally transitioning from the intermediate host to a human. More research is needed to confirm this theory and fill in details such as which species of bat the virus came from and which type of animal was the intermediate host. Scientists generally call this a “spillover event”, which is defined as the event in which a pathogen is transmitted to a member of one species from another species. In the case of SARS-CoV-2, there were actually two spillover events necessary to bring the virus from bats to humans!

As we said before, SARS-CoV-2 was named because it is very genetically similar to SARS-CoV, another coronavirus that caused a pandemic in 2003. Both of these viruses, along with MERS-CoV (Middle Eastern Respiratory Syndrome-Coronavirus) cause respiratory infections in humans and are thought to have originally come from bats. Other coronaviruses exist, too, and are not associated with bats. For example, “coronavirus SW1”, a completely new coronavirus, was discovered in beluga whale in 2008 and is not currently known to infect humans. As you can already see, there’s a lot of coronaviruses roaming this planet, but only one of these is causing the current pandemic.

https://jvi.asm.org/content/82/10/5084

Coronavirus invades our lower respiratory system (trachea and structures in the lungs), which is why difficulty breathing, shortness of breath, and a dry, non-mucus-producing cough are the most common symptoms associated with COVID-19. Although it is rare, the virus occasionally invades the gastrointestinal tract and causes symptoms like nausea, vomiting, diarrhea, and loss of appetite. These infections cause our bodies to mount an immune response in an attempt to kill any of our cells that the virus has infected and minimize viral spread and damage. This immune response is responsible for the fever and fatigue associated with COVID-19 and can even lead to some lung damage. At this time, scientists and doctors do not know whether this lung damage is long-lasting or how severe it might be. 

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