The Corona virus dominates our everyday life – a lot is talked about, discussed and reported. And of course, I also receive daily questions on this topic in my consultation hour, specifically in connection with Multiple Sclerosis. I had already written two weeks ago that it is extremely difficult to make definitive statements in view of the limited data situation – much is based on speculation and this does not exactly contribute to reassurance.
Therefore, I thought it might be quite useful to gather some general information and facts at this point, which might help individuals to better assess the situation and form their own opinion and attitude.
So I would like to start with some very general information – I hope this is not too superficial, but I often find in conversations with my patients that it is quite helpful to anticipate some basic things and not always presuppose this knowledge.
- What are viruses anyway?
- What distinguishes them from bacteria?
- Why is it often so complicated to treat viruses with medication?
Well, viruses are particles that contain genetic information but do not have their own metabolism. To reproduce, they use the metabolism of cells of a host organism – e.g. the metabolism of human cells. Therefore, viruses are obligate cell parasites, they cannot reproduce outside living cells not. This fundamentally distinguishes viruses from bacteria, because these have their own metabolism and can reproduce without the help of a host organism. Accordingly, bacteria, although they are also very small, are many times larger than viruses. Bacteria can still be seen with skill with the light microscope, to make viruses visible one needs an electron microscope. Because viruses are so small, special filters are also needed in respiratory masks to protect oneself effectively (e.g. when a doctor has to treat an infected person – and that’s why it would be nice if we had enough of these so-called FFP2/3 masks in the practices/clinics).
Viruses need a host
Virus particles are very simply constructed. Ultimately, it is just a piece of genetic information (DNA or RNA) that is surrounded by a protective coat, the so-called capsid. This “packaging” consists of amino acids. The capsid is therefore a protein (protein molecule), which also has antigenic properties – this means that an immune response can develop against it and thus it also plays a role in vaccine development. Some viruses also have a shell. This shell material also consists of proteins and lipids (“fats”) – these shell proteins also have antigenic properties.
Viruses can be classified according to their host specificity (i.e. whether they prefer to infect animal organisms or humans) or according to their organotropism – this means which organ system they prefer to infect (e.g. hepatitis viruses prefer liver cells, and corona viruses the cells of the upper respiratory tract).
During an infection, the virus enters the host cell. For this purpose, virus particles bind to certain receptors (attachment sites) on the cell membrane and are then smuggled into the cell interior. In the phase of attachment, the viruses are free and can be neutralized by antibodies, which have been formed e.g. by a vaccination. If this specific immunity does not yet exist (as is currently the case with the Corona Virus SARS CoV2), the risk of infection, i.e. the penetration of the virus into the host cell, is high.
Primary and secondary damage from viruses
Once inside the cell, the viruses begin to reproduce using the cell metabolism of the host cell, this so-called replication of the viruses occurs in different ways. Each virus has optimally adapted itself to the cell metabolism of its host in order to reproduce as effectively as possible. The infection thus sets in motion a multitude of processes that end with the production of new virus particles.
The production of new virus particles often leads to an “overload” of the host cell and its synthesis apparatus and then ends in the death of the host cell and the release of the new virus particles. This direct damage caused by the viral infestation is also referred to as primary damage and is distinguished from so-called secondary damage – namely the damage that occurs when the body’s own immune system reacts to the cell death and the “intruder” with an inflammatory reaction. For example, the severe respiratory syndrome that occurred during the SARS-Corona epidemic in 2002 is probably due to secondary immunopathological processes. The secondary damage caused by viral infections is also the reason why we sometimes even use targeted immunosuppressive drugs for severe viral infections.
Probably now you will understand the correlation, why in the past the thesis was pursued that Multiple Sclerosis (MS) is caused by a viral infection.
Medicines and vaccines against viruses
Furthermore, the explanations above should make it clear to you why it is absolutely not trivial to develop a drug against a specific virus. Because human-pathogenic viruses (i.e. viruses that make humans sick) use the synthesis apparatus of human cells, you cannot simply stop the reproduction, because you would inhibit your own cell metabolism, which is vital. Therefore, research focuses on preventing the introduction of the virus and blocking the assembly of the virus particles – and that is anything but simple. In any case, much more difficult than with bacteria, which have their own, specific metabolism that can be inhibited by antibiotics, without simultaneously blocking essential functions in the human body. However – just by the way – we are currently risking this advantage through unreflecting and unrestrained antibiotic use in animal breeding and the associated development of resistance.
Another important defense strategy is the development of a vaccine, e.g. by generating an immune response against the protein components of a virus (capsid, shell). But this is also anything but trivial and requires above all time.
I hope that the explanation is helpful in the context of the current Corona discussion. In the following article I will try to roughly explain how the immune defense against viruses works. The knowledge of this process is of interest in view of the evaluation of certain MS drugs in times of Corona.
