What you need to know before reading about COVID-19 and the virus that causes it
There are several types of coronaviruses but they’re not all like the one that causes COVID-19. The virus which causes COVID-19 or Coronavirus Disease is called severe acute respiratory syndrome coronavirus 2 or SARS-CoV-2.
Severe acute respiratory syndrome-related coronavirus is one species within one of four virus genera in the virus family called Coronaviridae. Corona comes from the corona or crown-like spikes on the surface of the virus.
In humans, coronaviruses “are included in the spectrum that causes the common cold as well as more severe respiratory diseases” like SARS and MERS (the latter two which were zoonoses, which means they transmitted from vertebrate animals to humans). The CDC says it’s rare for animal coronaviruses to infect people and then spread from person to person. But it has been seen before with:
- MERS-CoV (Middle East Respiratory Syndrome Coronavirus which causes MERS)
- SARS-CoV (a SARS associated coronavirus that causes SARS)
And now
- SARS-CoV2 (Severe Acute Respiratory Syndrome Coronavirus 2)
And when researchers see something transfer from vertebrate animals to humans it’s always a cause for concern.
Prior to COVID-19 the World Health Organization (WHO) has said “as the world is increasingly inter-connected, emerging zoonoses in one country can potentially constitute a threat to global health security. Ultimately, however, zoonoses matter not just because they are so common, but because they cause morbidity and mortality, high burden on health systems, but more importantly, it causes significant economic loses to the countries.” But it’s not the presumed zoonotic origin of the COVID-19 that is so threatening. It’s just that for nearly a decade the scientific community has acknowledged the “risk of a zoonotic pandemic” as a “major global threat to human health.”
The spread of the virus that causes COVID-19 is the “third documented spillover of an animal coronavirus to humans in only two decades that has resulted in a major epidemic,” according to the International Committee on Taxonomy of Viruses (ICTV). ICTV names the classification (or taxa) under which viruses fall under. The names are based on their “genetic structure to facilitate the development of diagnostic tests, vaccines and medicines” among virologists and the wider scientific community.
ICTV named the new virus SARS-CoV-2 “because the virus is genetically related to the coronavirus responsible for the SARS outbreak of 2003.” It’s important to note that the virus SARS-COV-2 and the disease it causes, COVID-19, have two different names (think of how HIV and AIDS have different names). ICTV said it hopes having different names “for the causative virus (SARS-CoV-2) and the disease (COVID-19)..will raise awareness in both the general public and public health authorities regarding the difference between these two entities . The CSG (ICTV’s Coronaviridae study group) promotes this clear distinction because it will help improve outbreak management and also reduce the risk of confusing virus and disease, as has been the case over many years with SARS-CoV (the virus) and SARS (the disease).”
So, we know that ICTV names the virus that causes COVID-19, SARS-CoV-2 because it is genetically related to the coronavirus that causes SARS but they’re not identical. “SARS-CoV infections have a higher mortality rate, while SARS-CoV-2 spreads much more rapidly.”
The ICTV CSG said it’s possible that the two identified severe acute respiratory syndrome related coronaviruses could be “poor representatives” for this type of virus. And as a result our current understanding of the fundamental aspects of this species of viruses is limited, and “as a consequence, our abilities to control zoonotic spillovers to humans.”
CSG said what could be helpful would be “extensive genetic analyses of large number of individuals representing diverse population from all continents … being translated into clinical applications.” They said such human-wise studies were “instrumental in identifying reliable predictive markers for specific diseases.” And therefore, “reasonable to expect genome-based analyses with a comparable species coverage will be similarly insightful for coronavirus.”
In general, viruses alone are very complex, let alone a virus that we know so little about.
Not all viruses are bad.
There are “friendly viruses,” we just don’t know that many of them. One example is bacteriophages, sometimes referred to as just phage. Yale Medicine said phage “can be weaponized to fight even the most difficult bacterial infections. This works because, unlike viruses that makes us sick, phages can only infect bacteria-and they are even selective about which bacteria they target. These phages are not rare; phages come from nature and are found nearly everywhere in the world.”
Viruses have their own genetic material (either DNA or RNA), but they need a host to replicate. That’s why they’re considered to be parasites of living cells.
They literally insert genetic material into a host cell and only after infecting that human cell are they able to reproduce. The viruses also mutate to adapt to the new host and escape from the immune system, generally speaking the stronger version survives.
When a virus infects a human, “they can embed small chunks of their genetic material into our DNA.” A 2016 study from the National Institute of General Medical Sciences said that “as a result of this ongoing process (which has been occurring for millions of years) viral genetic material comprises nearly 10% of the modern human genome, mostly derived from the retroviral genome during evolution.
Over time, the vast majority of viral invaders populating our genome have mutated to the point that they no longer lead to active infections.” For the virus itself, once they have injected their material into the host cell, they also pick up some of that host’s DNA, and they can also cause diseases that have long term effects for example how the human papilloma virus (HPV) can lead to certain cancers. But we face many viruses and like with a cold, our immune system overcomes many of them with limited damage. We do not have a cure for viruses, only treatments and vaccines. Vaccines do not cure viruses but they can prevent the virus infection and thereby prevent the disease.
Antiviral treatments treat viral infections, but they don’t work for every virus. The most successful antiviral treatments have been for HIV and are called anti-retroviral. Anti-retrovirals do not kill HIV, but in a way suppresses the virus. These treatments basically freeze HIV at its different life cycles so that it can’t replicate. The number of virus particles drop to an undetectable viral load in the blood, but the virus still successfully lives in the viral reservoir of the intestines.
Our immune system is our best defense against viruses. “For most viral infections, treatments can only help with symptoms” while the immune system fights the virus.
When the immune system recognizes something that isn’t supposed to be there (an unfamiliar antigen on a pathogen) it kills it. The immune system kills these invaders through multiple defense strategies either sending cells directly to attack the it, or by producing immune globulins called antibodies. Some antibodies destroy unfamiliar antigens directly, others make it easier for other cells to destroy, or prevent the entry or release of a viral particle to or from a cell. Once a healthy immune system has encountered an “invader” it remembers that invader, allowing it to develop a quicker response to defeating it in any future encounters (this is basically how active vaccines work). But that’s also why the first encounter may take longer for the body to destroy.
Researchers are working to identify a treatment for the virus and disease; a cure for COVID-19 or a way to eradicate the virus which causes it. New findings continue to emerge and are being published by the top scientific journals. There are hundreds of clinical trials being conducted around the world in hopes of finding a solution. Johns Hopkins Medicine said “why widespread and rapid transmission (of SARS-CoV-2) occurs is not completely certain.” We know that when it comes to the virus “human to human transmission occurs through close contact.” This is why public health officials have advised social distancing.
Aerosols is a common easy way for viruses to spread from person to person. Droplets of saliva are generated not only when we cough or sneeze, but also when we breath or talk. Researchers suggest wearing a mask as a means of preventing infectious saliva droplets from projecting into the air, and disinfecting indoor areas to block dissemination of those droplets.
ICTV’s Coronaviridae study group (CSG) said that while the “full spectrum of clinical manifestations associated with SARS-CoV-2 infections in humans remains to be determined, the independent zoonotic transmission of SARS-CoV and SARS-CoV-2 highlight the need for studying viruses at the species level to complement research focused on individual pathogenic viruses of immediate significance.” And that doing so will enhance our “preparedness for future outbreaks.”
The world is currently working together on sequencing as many samples of SARS-CoV-2 as possible. Doing so will help us to better understand the spread of the virus and therefore empower us to better control it.
This brief has been reviewed by Prof. Dr. Jorg Hofmann, Lead Scientist Diagnostics, Department of Virology, Institute of Virology at the Charite University Hospital Berlin.
