What are the new versions XD, XE and XF waiting for?


We are going to discuss, against the background of evolution, the appearance and development of new viral strains, focus on the Sars-Cov-2 virus, which we have been living with for two years now.

RNA viruses can be particularly variable

Evolution has two engines that drive it: genetic variability and natural selection. Genetic variability is caused by errors in the replication of genetic material. These errors are remarkably rare given the amount of genetic material that multiplies in each generation and the speed of the process. However, the huge number of constantly multiplying microorganisms or viruses is a rare occurrence. Thus mutations accumulate in the population.

Replication of genetic material is more accurate in organisms and structures that use deoxyribonucleic acid (DNA) as information support because the apparatus that carries it (DNA polymerases) may have error correction mechanisms.

However, when the genetic material is ribonucleic acid (RNA), the replication mechanism is more inaccurate and errors are more frequent. Consequently, RNA viruses are more prone to mutation than DNA viruses or bacteria and other cellular organisms.

There are highly variable RNA viruses that make up a population of different populations in the same infected person. This is the case, for example, with the hepatitis C virus. The term “quasi-species” is thus used to describe the coexistence of a large number of variants of the virus that are not mutually exclusive.

Coronavirus has the ability to adapt to different environments

Natural selection, on the other hand, is a process in which some organisms have greater reproductive success than others in a given environment and can move competitors to become dominant or exclusive.

As it is easy to understand, mutations that give the environment more reproductive success will become more common in the population and the organisms that have them will adapt better to this environment. In fact, it happens that the most successful reproductive variants predominate, and if the variant can colonize the new environment, it will do so and win in it, at least temporarily.

Coronaviruses are small RNA viruses with high variability. This allows them, as a group, to adapt to different environments (infect different types of animals) and to constantly generate new variants, the relative abundance of which will depend on their reproductive success.

In this way, since the SARS-CoV-2 coronavirus infected the first humans in Wuhan, from which the pandemic originated, new variants of the virus are constantly emerging. Its rise and fall are constant, as are the waves in the sea.

These variants are cataloged in lines that form detailed genealogies, allowing for strict epidemiological monitoring of the pandemic, as is done for others such as influenza or AIDS.

As of today, it is estimated that nearly 500 million cases of coronavirus have been reported worldwide, with more than six million deaths. Given the millions of virus particles that occur in each infected person and the frequency of mutations, the emergence of new variants of the virus is an inevitable event that will remain constant in the future.

The arrival of a new series of variations

Recently there was talk of a new series of variants of Sars-Cov-2, the name of which begins with the letter X: XA to XS. These variants are recombinants of the other strains already described above.

Their origin is not the same as I described in previous paragraphs, but they are produced during co-infection of the same cell with two coroviruses of different strains. When two viruses replicate in the same cell, their genetic material can combine to form a new virus that combines the characteristics of both parents. If this new virus is reproductive more successful than the rest of the population, it will dominate and become prevalent.

The new recombinant strains that have aroused public interest are called XD, XE and XF and are found mainly in France, Denmark and the United Kingdom.

All three contain material from strain BA.1 (icmicron) and, in the case of variants XD and XF, from the delta variant. Since these variants have been identified in certain quantities in these countries, it is expected that their prevalence will increase as they have sufficient reproductive success to stand out.

The available data suggest that these variants may be more contagious than the previous ones, but there is no significant data to suggest that they will be more viral than we know.

Recombination of the viral genome is a process that requires co-infection and the formation of a new and successful recombinant molecule. The process occurs because a large number of viruses and infections make its recurrence rare. The formation of new viruses by this system is the emergence of pandemic strains of influenza that occur recurrently in 20 to 30 years as a result of a mixture of influenza viruses of different origins.

The process facilitates the division of the genome (as well as RNA) into several molecules in the case of the influenza virus. In the case of coronavirus, the process must be more rare because its genome is organized into a single molecule and recombination is required and not just the packaging errors that produce genome mixtures in the influenza virus.

And this is the current situation: new options are emerging that enter the epidemic monitoring system of the Centers for Disease Control in Europe (ECDC) and North America (CDC).

The ECDC distinguishes three levels for organizing the progressive intensity of new viral variants: monitored variants (XD and omicron BA.3), interesting variants (icmicron BA.4 and BA.5 strains), and concern variants (delta). Variant and BA.1 and BA.2 omicron strains). Options XE and XF have not yet reached compliance levels to be classified as supervised options.

For its part, the World Health Organization also includes only the XD variant among those that are classified as further.

What the future effects of these new variants will be on the population and the evolution of the epidemic, we do not know exactly, because evolution is a combination of chance and necessity; But we can have certain expectations based on what we know from evolution and past epidemics.

What is to be expected from this option

We can define pathogen virulence as the number of severe or very severe cases relative to the total number of infected. With proper caution, virulence of pathogens is generally reduced during coexistence with the host.

This can be explained by the fact that the reproductive success of the pathogen is greater, the less damage it does to the host and, consequently, the more capable it is of transmitting the pathogen. A dead dog does not transmit rabies. For this reason, less viral variants are more prevalent than others that restrict or exclude the mobility of a sick animal or human and prevail in society over time.

On the other hand, the immune system learns to deal with this virus by controlling its multiplication and modulating the response (which is necessary in case of corovirus infection to worsen the disease).

Therefore, and in the end, we should expect that new variants of coronavirus will appear again, the spread of which in the press and forcing them under special supervision of international organizations. But we can reasonably expect these new options to be less viral. Thus, pandemic sequential waves should be smoother and the hospital response, if any, would not be significantly affected.

Antonio G. Pizabaro. Professor of Microbiology, Department of Health Sciences, Institute of Multidisciplinary Research in Applied Biology, Navarre Public University.

East article Originally published Ს Talk. You can read Here.

Source: El Diario


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