CORONA PANDEMIC: HOW VIRUSES REALLY WORK

Since the topic of viruses is very popular due to the current Corona pandemic, some general factual background information on viruses is included here. From a biological perspective, it is exciting to understand in more detail what processes the small particles in our body produce. Without our cell mechanisms they would not be able to spread at all, which is why it is to their advantage not to cause too much damage to our organism. They could also bring us medical benefits, for example in cancer research.

What is a virus? Why are viruses not living beings?

According to the official definition, living things are made up of cells. They engage in active metabolism, growth, reproduction and respond to stimuli ¹ . Viruses are not cells and do not have their own metabolism , because their existence consists only of a protein capsule that contains genetic information. Although some viruses have a shell around their capsule that resembles a cell membrane, this still does not allow them to carry out independent metabolism ² . So a virus cannot eat and excrete waste like animals and humans or even bacteria in a primitive form. By the way, viruses are not referred to as parasites, as the term is limited to living beings and is more commonly used for bacteria, protozoa and worms, which are harmful to the infected organism.

How do viruses reproduce?

The goal of viruses is to maintain their own existence. It is of great advantage to multiply over a large area as quickly as possible. Since, as explained above, this cannot happen independently, a foreign cell is called a so-called host needed. When it comes to viruses, these are primarily people and animals and their cells. A virus therefore absolutely needs cells from a living being in order to nest there and use the host cell for its own reproduction ² .
There are two main mechanisms that the pathogen uses: On the one hand, transmission from one host to another, on the other hand passive reproduction within the respective host.

Step 1: Transfer

There are several ways a virus can travel from one host to another:

1. Aerosol droplet infection :
   The viruses are transported out into the air via tiny droplets of secretion from the respiratory tract (lungs, nose, mouth). There they usually fly around invisibly in the immediate vicinity of the carrier (e.g. a human). Sneezing and coughing in particular release many of these secretion droplets. Because they are so light, they can stay there for a few minutes and their range is 1-3 meters depending on the species ³ . Examples of this type of transmission are classic influenza (flu) viruses and the SARS-CoV-2, which is currently spreading everywhere and can trigger corona disease.
2. Direct transmission :
   A virus is passed on through direct salivation or physical contact. For example, the herpes virus, which can cause fever blisters on the lip, is transmitted when kissing. With this virus, this only happens at the time of the outbreak, i.e. when the symptoms are currently occurring ² .
3. Sting or bite from an animal :
   Viruses can also spread using a so-called vector, a transmitter. The animal itself or its cells only serve to bring the viruses to the actual host without the vector itself becoming ill. A popular example of this is the rabies virus, which causes the disease rabies. Animal bites infected many people between 1989 and 2011 ² .
4. Body fluid or blood during sexual intercourse: 
   Viruses that are transmitted in this way have optimal development conditions when they are exposed to no light but a lot of moisture. They are transmitted during sexual intercourse via body fluids exchanged there. They are also found in the blood, and there is another route through smaller cuts or injuries. HIV, the virus that causes AIDS, is a prime example of this ² .
5. Fecal-oral:
   The viruses are transported to the outside via the stool and absorbed orally by the next host. This transmission route is conceivable if there are poor hygiene conditions, such as those known from earlier times or from third world countries. This should not happen if the toilets are clean and you wash your hands regularly after using the toilet. Hepatitis A viruses use the fecal-oral route of spread ² .
6. Indirect smear infection:
   Surfaces of objects serve as platforms for the viruses to reside on until another host comes and touches the object. All you have to do is unconsciously touch your face and you have already picked up the virus.

Many viruses can be transmitted via several of the routes mentioned. The current virus SARS-CoV-2, for example, spreads via aerosol droplet infection, direct transmission from hugs and indirect smear infections on surfaces.

Step 2: Propagation

After a virus has been transported from one host to the next via one of the above-mentioned routes, it uses the mechanisms of the host cells to reproduce itself. This process is described using an infected human cell:
Our cells have a cell nucleus in which the so-called DNA is located, on whose strands our genetic material is located. This enormous store of information is constantly used for metabolic processes and everything that happens in our body. Most cells divide in the normal cell cycle to destroy old ones so we can grow and stay healthy. In addition, small sections of DNA are copied onto the so-called RNA, which transports the overwritten information from the cell nucleus. There it is used to give the cell organelles instructions for specific metabolic processes. All of this is relatively complex and abstract; for the virus to multiply, it is enough to know that we have important information on the DNA and RNA.

Viruses also have such information in their capsule. These are available either as DNA or as RNA. The virus uses proteins on its surface that can dock onto receptors on the respective human cells. Our cells usually cannot recognize that it is a foreign body and open the gate. The viruses transfer their genetic information into our cells and these then begin to copy this actually foreign DNA or RNA and follow the “instructions”. As a result, our cell then assembles several copies of the respective virus, which multiplies quickly. You can imagine this intrusion like a Trojan horse that sneaks in the bad guys unnoticed ² .

To what extent are viruses important for the human organism?

Many viruses we know can cause symptoms and illnesses in us. For example, the human immunodeficiency virus (HIV) attacks important cells in our immune system, whose function is then disabled. In healthy people, the affected T helper cells protect the organism from pathogens such as bacteria, other viruses, fungi, etc. As soon as they can no longer do this job, we are extremely susceptible to illness. An acquired immune deficiency syndrome develops, which is also known as AIDS. This leads to those affected developing secondary diseases, such as tuberculosis or pneumonia, which the immune system can no longer combat. This can ultimately be fatal without the right medication ⁴ .
But not all viruses are a danger to us and they may even be able to help us cure diseases in the future:

Viruses, evolution and their benefits for humans

Scientific research has shown that a significant portion of our human genome comes from viruses. These have obviously already been incorporated into the DNA of our monkey family tree and later also of modern humans. Researchers assume a viral share of 8 – 43% ⁵ . If even a small number of these are true, it is obvious that viruses have played a central role in determining which genome sequences are in our genome. Since evolution is based on the “survival of the fittest” principle, these originally alien phases should not have harmed us. They may even have made a positive contribution to our development.
Certain viruses could have another benefit for our healthcare system: viruses are being programmed so that they attack cancer cells. Cancer researchers have taken advantage of the fact that the genetic material of a virus can penetrate our cells almost unnoticed and change their gene activity. Certain viruses can be weakened and modified in the laboratory so that they specifically kill tumor cells or inhibit their activity. This is associated with fewer complications than chemotherapy, because it also damages healthy cells ⁶ . Research into these modifications of viruses to fight cancer is still ongoing, but it gives us hope for better support in healing.

Conclusion

Viruses are tiny particles that do not belong to any living organism. They need a host to reproduce and other hosts to spread. There are many viruses that can cause disease, many that do not harm us, and possibly some that are useful to humans.

How we can protect our body and our immune system from pathogens such as viruses, and what our own immune cells do every day, will be explained in the next article.

¹ Doccheck Flexikon: Living beings. [https://flexikon.doccheck.com/de/Lebewesen; March 25, 2020].

² Bütikofer, Markus; Hopf, Zensi; Rutz, Guido; Stach, Silke and Grigoleit, Andrea (2015): Human Biology 1: Basics, Metabolism and Defense Systems. Zurich: Compendio Educational Media. pp. 139-141, 242.

³ Dochcheck Flexikon: droplet infection. [https://flexikon.doccheck.com/de/Tr%C3%B6pfcheninfection; 03/28/20].

⁴ Zschokke, Samuel (2018): Human Biology I: Anatomy and Physiology – Infectious Diseases. Basel: University of Basel.

⁵ Heinemann, Pia (2016): How viruses sneaked into the human genome. In the world. Berlin: Axel Springer SE.

⁶ Till, Ulrike (2018): Using viruses to fight cancer. SWR.