On Mutation of Viruses: Coronaviruses and Other Species

Viruses, mutations, strains - these three words are on everyone's lips today. The coronavirus pandemic, which has engulfed almost the entire planet, made us wonder where the diseases that radically change the life of mankind come from.

In the twenty-two years of the 21st century alone, we have experienced five epidemics that have posed a serious challenge to world medicine. Each of them is caused by viruses, but what is surprising is that after a certain period of time the virions (viral particles) return, but in a slightly modified structural form. So in 2002-2003, 27 countries of the world faced an epidemic of SARS, from which more than 800 patients died. And this was only the beginning, because further mankind was waiting for:

  • swine flu A / H1N1 in 2009-2010 - the death rate reached almost 19 thousand people;
  • H5N1 and H7N9 avian influenza 2003-2017 – more than 450 cases died;
  • Middle East Respiratory Syndrome (MERS-CoV) is an acute respiratory viral infection caused by the human pathogenic coronavirus MERS-CoV. The mortality rate is relatively low - 430 patients in 2012-2015;
  • Ebola hemorrhagic fever, in 2014-2016 and claimed 11,300 lives;
  • COVID-19 is the current pandemic caused by the spread of the SARS-CoV-2 coronavirus. Taking 5.6 million lives.

It is easy to see that some designations of viruses have something in common. This is not surprising, because they can be caused by mutated viruses of the same type. Let's try to figure out what a virus mutation is and why it happens.

What is a virus, its structure and features

The world of microorganisms is represented by several separate species, each of which is fundamentally different from the others. Viruses belong to this group, although they have their own characteristics that are not characteristic of the rest of the representatives of the animal and plant world invisible to the naked eye. Firstly, they do not have a cellular structure and protein-forming systems. Secondly, they have pronounced cytotropism and intracellular parasitism.

Scientists who study viruses have calculated that there are more than 10 of these microorganisms on Earth. They have different shapes, sizes and life cycles, but several properties unite all viruses:

  • the presence of a capsid - a protective protein structure;
  • genome, which consists of DNA or RNA and is located inside the capsid;
  • supercapsid - a shell that covers the capsid, but it is not present in all types of viruses.

When a virus enters a host cell, it begins to multiply rapidly. As a result, many copies of the causative agent of the disease appear, which then affect other cells of the body.

In the process of reproduction and transmission of the virus, sometimes there is a change in the genetic material that is in the genome. This is what is called a mutation.

The more viruses circulate and replicate more often, the greater the chance of new strains emerging.

Such a mutation can create viruses that are easier to adapt to the external environment, have a high contagiousness, and cause radically different symptoms and course of the disease. This process is called evolution.

The main causes of virus mutations

Every year new strains of viral infections appear in the world. This is explained by the evolution of viruses, which occurs very quickly and can occur in two ways:

  • recombination: in this case, microorganisms infect the same cell and exchange genetic material with each other;
  • mutation: a change in the sequence of DNA or RNA chains occurs within the virus itself.

Recombination is inherent in the influenza virus, because it has eight RNA segments at once, each of which carries from one to several genes. When two different strains of the same pathogen enter the body, new microorganisms with mixed segments are produced.

Mutation also produces new strains, but the process is very different. For the emergence of a new strain, simultaneous infection with two different pathogens is not necessary, since all changes occur when the virus is copied. It is known that DNA viruses change much less frequently than RNA. Scientists explain this feature with one important difference: for DNA viruses, in the process of copying, they need DNA polymerase, an enzyme that enters the host cells. It is she who detects and corrects errors, preventing the emergence of modified viruses, but virions are sometimes able to bypass this mechanism.

The RNA polymerase involved in the replication of RNA viruses does not have this ability, so no correction takes place. Accordingly, the likelihood of the emergence of new strains of viruses is high.

Viral diseases with multiple types of strains are actually not that many. The most famous and most common mutations occur in influenza, HIV, coronavirus. For example, during the entire existence of SARS-CoV-2, thirteen different forms have formed. The COVID-19 pandemic began with a form that was discovered in December 2019 in the Chinese city of Wuhan.

Consequences of virus mutation

Is mutation good or bad? This question cannot be answered unequivocally, because in each case the result is different. For some diseases, the mutation of virions becomes an opportunity to “feel” even more comfortable in the body, while for others, it leads to the fact that patients get sick easily and recover quickly.

In HIV infection, gene mutation to form new strains is one of the main causes of drug resistance. The thing is that to block HIV replication, a reverse transcriptase inhibitor is used, the mechanism of action of which is to combine with this enzyme in the virus. Without its participation, the virion cannot copy the genome, but some viral particles mutate precisely in the reverse transcriptase gene, so the drug does not work on them. For this purpose, for the treatment of HIV, a combination therapy of several drugs that affect different cycles of the virus development is used.

Influence on virus detection and vaccination process

Mutation, which results in new strains, poses serious challenges for laboratory diagnostics. It is important that the new forms do not fall out of the scope of the identification methods that are used today. The WHO Global Laboratory Network has established a task force to study the evolution of SARS-CoV-2. Its representatives take samples from patients with new, atypical symptoms and send it for further research. Such steps make it possible to monitor the emergence of new strains, their impact on humans, and the effectiveness of drugs on new forms.

To date, the diagnosis of coronavirus is performed by 100% effective methods, as it is determined by the RdRp (ORF1ab) and N genes, which do not mutate at all.

The situation with vaccination is a little more complicated : a new strain of coronavirus “omicron” appeared a few months ago, dealing a blow to the efforts of scientists and doctors who developed vaccines against COVID-19. Although less of a health hazard compared to previous forms, he questioned the efficacy of vaccination. Thus, tests of the Pfizer vaccine found that it protects against omicron by only 22.5%. This conclusion was made by the experts of the African Research Institute of Health in Durban (South Africa). To do this, they took blood plasma samples from 12 vaccinated patients who fell ill with this particular form of coronavirus. The study was based on the determination of neutralizing antibodies in the body. At the same time, they made the assumption that the vaccine would make the course of the disease easier, protect against the occurrence of complications.

In the past, the effectiveness of vaccination with a biotech drug was evaluated by British scientists. Their results were more optimistic: a third dose of mRNA vaccines from Pfizer and AstraZeneca increased the body's defense against omicron by 75%.

But not everything is so pessimistic. Despite an increase in the number of patients with coronavirus of the Omicron strain, there are few hospitalizations among those vaccinated. Of course, the outbreak of the pandemic is still ahead, but optimistic forecasts have been made: the evolution of SARS-CoV-2 is most likely nearing completion. The purpose of the virus is not to kill a person and die itself, but to continue its life cycle, for which it needs to mutate into a weaker form.

COVID-19 is unlikely to completely disappear from our lives. But its annual appearance during the season of respiratory diseases with milder symptoms will not be so dangerous. So the mutation of viruses can be a positive process.

Sources
  1. Website of the Ministry of Health of the Moscow Region. – Epidemics of the 21st century: 5 dangerous viruses of recent history.
  2. Pharmaceutical Encyclopedia. - Viruses.
  3. Internet portal “Hitech”. – Scientists have calculated the number of viruses on Earth. There are more of them than there are stars in the universe.
  4. Khan Academy website. – Introduction to viruses.
  5. News portal “Liga. Business”. – Coronavirus evolution: why the virus mutates and how to diagnose new strains.
  6. Wikipedia - SARS-CoV-2 strains. Pivot table.
  7. Khan Academy website. – Evolution of viruses.
  8. Network publication “Forbes.ru”. – Pfizer's vaccine against the Omicron strain was estimated to be 23% effective.
  9. News portal “Gazeta.ru”. - The infectious disease specialist spoke about optimistic forecasts for the Omicron strain.