Infections are becoming more aggressive or vice versa: what should we prepare for?
Viruses mutate and become more contagious and can pass through more barriers in the human body. But it is believed that many infections weaken over time. High Tech is looking into whether infections will become more aggressive, and if not, why.
A pathogen that lives in your body for years is a harmful neighbor or a bloodthirsty killer. There are enough arguments in favor of the first, but everything is not so clear.
Is it advantageous for a pathogen to be aggressive or vice versa soft?
One of the first researchers to suggest that a pathogen is more effective if it acts gently was the French chemist Louis Pasteur. The researcher during his observations noted that anthrax may become less aggressive.
Similar conclusions were made in 1875 by a researcher from Belgium, van Beneden: he observed parasites and decided that they were exploiting an alien organism, but they were doing it sparingly. The same conclusion was summed up by the bacteriologist Theobald Smith in 1904 and confirmed that all parasitic organisms do not set themselves the goal of causing irreparable harm to the host.
Based on these studies, it can be concluded that infections may become less severe over time.
Why do infections kill so many people, how can they be weak?
Bacteriologist Theobald Smith studied highly pathogenic bacteria, since viruses were not yet known at that time. The scientist called such bacteria new, which did not have time to get used to and adapt to life with a person.
This means that over time, highly pathogenic bacteria, in his opinion, will become less toxic and will be minimally protected from the host’s immune response. Such coexistence, according to Smith, means that no one will kill each other. Therefore, pathogenic bacteria, as we know them today, will cease to have a great negative impact on us.
Smith stated that most infections have relatively low mortality. Even if it is 25% or 50%, the person still wins. This is if you do not take into account the values of humanism, he emphasized. Means infections constantly lose. Nevertheless, the virologist did not undertake the task of predicting how many years later the virulence would decrease so much that the microbe would become completely harmless.
So was Smith right or not? How to understand that the virus has become less aggressive?
Proving this is not so easy, even today. To confirm or refute Smith’s ideas, we can use as an example two populations of pathogens, between which there are several generations. The next step is to compare their virulence.
But how to do this is not clear.
Virulence is the degree to which a microorganism or virus can cause disease or death. In other words, how much a particular infection harms the host. But this indicator can be calculated in different ways, it may depend on the characteristics of the disease and the project of a particular study.
For example, if scientists conduct an experiment on laboratory animals, then virulence is measured by the dose of the pathogen that can cause symptoms of the disease (ID50) or kill (LD50) half of the experimental group.
Another measure of virulence is the number of viral particles of an infectious agent required to infect an organism. In general, virulence depends on the properties of the virus, as well as on the susceptibility of a particular organism.
In the case of human infections, this is difficult to calculate: researchers do not often resort to experiments with infecting people, so doctors use different metrics to assess virulence. For example, someone takes into account the mortality of the host, someone the frequency of development of pathologies or individual side effects.
Is the coronavirus also getting weaker?
During the two years of the pandemic, many strains of SARS-CoV-2 have appeared, for example, alpha has become more contagious and deadly, beta has learned to avoid immunity, and a new variant, omicron, has become better than others to hide from antibodies. But it didn’t become more virulent.
If you build SARS-CoV-2 into the Smith system, then it will be a new virus that has not yet learned how to interact with people. Therefore, for now, at the first stage, the virus simply mutates and increases its properties arbitrarily. This will continue until it reaches a steady state. Then the virus will begin to evolve more naturally.
Nevertheless, the researchers note that in addition to reducing virulence, there is also the property of escaping immunity. Therefore, it is not yet possible to draw an unambiguous conclusion that SARS-CoV-2 is becoming more or less aggressive.
Is it possible to influence the virus, make it less “evil”?
Yes, mass vaccination not only does not affect the aggressiveness of pathogens, but also allows you to completely get rid of them. For example, this happened with smallpox, and scientists hope that the same will happen with polio in the future. But such an algorithm only works for vaccines that protect against infection, in other words, give sterilizing and lasting immunity.
According to experts, low rates of vaccination may affect the growth of virulence.
So far, we do not have a definitive answer whether pathogens are getting weaker or stronger: we must wait until researchers develop an accurate analysis algorithm and apply it until they see global shifts and changes in virulence. So far, the only way to slow the development of the pathogen is through vaccination.
