Coronavirus SARS-CoV-2: what kind of virus is it?

The coronavirus called SARS-CoV-2 has spread at breakneck speed. It is highly contagious and can lead to the severe illness of COVID-19. It appeared in late 2019 and has infected millions of people ever since. But why was this pathogen not known before, and where does it come from? What are viruses, and how do they differ from bacteria? In the following article, we will inform you about the peculiarities of viruses, paying particular attention to the SARS-CoV-2 coronavirus and its route of infection.

Where does SARS-CoV-2 come from?

This question about the origin of the virus takes work to answer. The group of coronaviruses has long been known in animals, especially bats. There are various theories as to how SARS-CoV-2 came about.

Researchers suspect that the SARS-CoV-2 virus passed from animals to humans because it was first detected in people at a fish market in Wuhan (China). However, it is still unclear which animals are involved. According to a report by the World Health Organization (WHO), bats are conceivable as the original carriers of the virus. An intermediate host could have played a role in the transmission, but this has not. For example, pangolins, civets, mi,nk or martens are questioned.

It is also discussed whether the virus might have originated in Southeast Asia. Samples taken from bats were examined there in 2010, and viruses were discovered similar to today’s SARS-CoV-2 coronavirus.

Another possibility is that the virus entered Wuhan via refrigerated or frozen food. The WHO has also investigated this theory and considers it fundamentally possible. From the point of view of many researchers, however, there is not much to say about this thesis.

Another theory says the spread of SARS-CoV-2 could result from a laboratory accident. The experts at the WHO currently rate this hypothesis as extremely unlikely.

 

Is SARS-CoV-2 a new virus?

SARS-CoV-2 is an entirely new variant of the coronavirus that was previously unknown. However, there is a genetic relationship to SARS-CoV-1, which made headlines in 2003. Also, both coronaviruses, SARS-CoV-1 and SARS-CoV-2, use the same receptor (ACE2) on human cells in the airways. A receptor is a docking point of a cell, which is used by viruses, for example, to attach themselves to cells and then penetrate them.

It is suspected that SARS-CoV-2 may have arisen from spontaneous changes in the genetic material (mutations) of another, closely related virus. These changes may have allowed the viruses to spread from animals to humans.

What is the name of the receptor that helps the SARS-CoV-2 coronavirus to enter human cells?

The SARS-CoV-2 coronavirus uses the so-called ACE2 receptor as a docking point in the human body. The abbreviation stands for “angiotensin-converting enzyme 2”. The ACE2 receptor is found in the lungs, heart, kidneys, vessels and gastrointestinal tract, among other places. SARS-CoV-2 uses a particular spike protein to dock.

 

The group of coronaviruses – which other viruses belong to it?

Coronaviruses are named because of their crown-like appearance under the electron microscope (lat. Corona = “crown”). They range in size from 75 to 90 nanometers, are found worldwide, and belong to RNA viruses.

The genome of RNA viruses consists of ribonucleic acid. This has an essential function in converting genetic information into proteins. In addition to the RNA viruses, there is a group of DNA viruses whose genome consists of deoxyribonucleic acid (DNA). RNA viruses also include other pathogens, such as measles or Ebola viruses.

SARS-CoV-2 and two other subtypes – SARS-CoV-1 and MERS-CoV – belong to a separate group within the coronavirus family. All three representatives of this group can cause respiratory infections in humans, ranging from harmless colds to fatal, severe pneumonia :

• SARS-CoV-1 is a coronavirus unknown until 2003 and caused severe acute respiratory syndrome (SARS).
• MERS-CoV first caused respiratory infections (MERS, Middle East Respiratory Syndrome) in the Middle East in 2012, which, like SARS-CoV-1 and SARS-CoV-2, can take very different courses.
• SARS-CoV-2 first appeared in China in 2019 and causes the disease COVID-19, which usually causes mild, flu-like symptoms. If the course is severe, it can lead to pneumonia, sepsis (blood poisoning) or multi-organ failure. Longer-term symptoms after the acute illness has subsided are also possible. This includes, for example, shortness of breath.

How are coronaviruses structured?

An essential characteristic of the coronavirus is its shell, which surrounds the genome. This envelope protects the genome when the virus is outside a host cell. At this stage, the virus is infectious and is referred to as a virus particle or virion.

The shell consists of lipids (i.e. fats) in which proteins (proteins) are stored. It is destroyed by water and soap. For this reason, washing your hands thoroughly with soap is an adequate protection against infection with coronaviruses.

How does SARS-CoV-2 become infected?

The so-called spike proteins are embedded in the SARS-CoV-2 virus envelope, which protrudes outwards from the envelope. Via these proteins, the virus can attach itself to the so-called ACE2 receptor in some human cells, especially those in the respiratory tract.

It can then penetrate the target cells using a unique mechanism. There, it releases its genetic material, the RNA, and uses sophisticated machinery to cause the target cell to produce many new virions. It is assumed that every single infected cell releases 100 to 1,000 virions, which can then attach to other cells or be transmitted to other people via droplets. So-called aerosols, droplets a few micrometres in size emitted when speaking and breathing, play a vital role in transmission.

 

Is there a drug against SARS-CoV-2?

Research into a drug against SARS-CoV-2 is still in full swing. The anti-inflammatory glucocorticoid dexamethasone is one of the most promising drugs currently used to treat coronavirus infection.

Remdesivir, developed initially as an Ebola drug, is also used to treat an infection. It is said to inhibit the spread of the coronavirus in the body and positively affect the healing process. The prerequisite, however, is that the drug is administered as early as possible.

Other therapeutic approaches include monoclonal (i.e. artificially produced) antibodies and convalescent plasma, i.e. the blood plasma of people who have already survived an infection with the coronavirus.

Paxlovid is also considered promising for preventing the virus from multiplying in the body. The aim is to reduce the risk of hospitalization or death if the drug is administered early.

Is there a vaccination against SARS-CoV-2?

Vaccine development is now quite advanced. Various vaccines have been in use for some time and have been shown to have a high protective effect against severe disease progression. The vector vaccines from Johnson & Johnson and AstraZeneca are currently approved in the European Union, the mRNA vaccines from Moderna and BioNTech/Pfizer, and the protein-based vaccine from Novavax.

Viruses, bacteria, fungi – what’s the difference?

Many microorganisms can cause infectious diseases. These include bacteria, viruses, fungi and parasites. These pathogen groups are assigned to different groups of living beings in biology:

• Prokaryotes (nuclear, meaning there is no cell nucleus): bacteria
• Eukaryotes (nucleated, there is a nucleus): fungi and parasites

The tiny viruses occupy a unique position. Strictly speaking, viruses are not living beings since they do not have their metabolism. They, therefore, need foreign cells, the host cells, for their reproduction. Host cells can be plant cells, animal cells or human cells. Outside of their host cells, viruses can sometimes survive for a long time and remain contagious.

 

Why don’t antibiotics work against viruses?

All of the groups mentioned are distinguished by their unique design. This concerns, among other things, the presence, structure and composition of cell components such as:

• cell wall
• cell membrane
• nucleic acids (genetic material)
• Ribosomes (protein factory)

These differences in the anatomy of the cells are a prerequisite for the accuracy and effectiveness of many drugs, such as antibiotics. Antibiotics develop their effect on the cell wall or the ribosomes of bacteria. Because these components are absent from viruses, antibiotics are ineffective against infections caused by viruses. This is also the reason why antibiotics cannot be used in COVID-19.

What diseases are caused by viruses?

Viruses can cause a wide range of diseases in humans. These range from harmless illnesses such as the common cold, superficial gastrointestinal infections, cold sores or warts to severe infections such as hepatitis (inflammation of the liver), rabies or AIDS. Some childhood diseases, such as measles, mumps, rubella or chickenpox, are also caused by viruses.

How can viruses be transmitted?

Not all viruses are equally contagious. For some, intensive contact is necessary for transmission from person to person. With other viruses, it is sufficient if people are in the same room with others; direct transmission is irrelevant. A distinction is made between the following transmission routes:

• Infection via food: Food contaminated with viruses goes directly into the stomach and intestines and can disrupt the functioning of the digestive system.
• Smear infection: This transmission route is called contact infection because the disease occurs during touching. Shaking hands or contact with objects to which pathogens are attached, such as doorknobs or handrails on buses and trains, is sufficient for this. If the hands are brought to the face after touching these surfaces, infection can occur via the mouth, nose or eyes mucous membranes.
• Droplet infection: When infected people cough, sneeze, or speak, tiny droplets containing the viruses become airborne. Infections can occur if others inhale them or if they get directly onto the mucous membranes of the nose, mouth or eyes.

Coronaviruses, including SARS-CoV-2, are transmitted from person to person via droplets containing the virus and sometimes also via surfaces contaminated with the virus.