Since the outbreak of the covid-19 pandemic, I have been waiting for a news article such as the following:
Or more precisely, I’ve been waiting to learn of a less violent version of SARS-CoV-2 (weaker symptoms) to be identified.
And what’s the downside? Well the new virus is more contagious.
So why was I waiting for the news of a weakened virus – you ask.
When examining the world of pathogens (disease agents) – hosts (patients) interaction, the pathogens can be divided into biotrophic and necrotrophic. Necrotrophic pathogens are parasites that kill their host and then feed on the dead matter. An example of such a pathogen is the bacterium Bacillus thuringiensis israelensis.
The bacterium produces a toxin that is released in mosquito larvae guts and kills them. The bacterium then consumes the larval corpse.
Biotrophic pathogens require their host to stay alive.The best example of biotrophic pathogens are viruses. The virus multiplies by injecting its genetic material into the host’s cells and therefore it cannot multiply itself without a live host. And this is the point where evolution kicks into play.
A virus must spread to new hosts, so the more contagious the virus is, the more likely it is to survive.
If the virus kills its host and carrier fast, it will multiply for a short time, and its chances of infecting new hosts will decrease. It’s important to remember that viruses mutate very quickly so virus populations change at an incredible rate. As time goes on, mutations that will keep the host alive longer but will be more contagious will be more successful and therefore will take over the previous virus population. This will continue until we reach a virus that does not harm the host but infects everyone.
In this way epidemics break out and disappear even if the population has not developed resistance or no vaccine is available.
The more difficult we make the infection process (by social distancing, wearing masks and also by “herd immunity” where much of the host population has been exposed), the more likely it becomes that a virus population that is less lethal and more contagious will evolve allowing the virus to infect over a longer time period. The result is that the virus “weakens”- or the hosts show weakened symptoms and are less susceptible to it.
This is good news. But we are not there yet. Currently, the virus strains are still dangerous and may be lethal and so we will all have wait for an effective vaccine before we are released from isolation, distancing and wearing masks. But know this fact, in the background, biology is doing its thing.