Why do pathogens kill the host they’ve infected?

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If reproduction of itself is why pathogens infect hosts, wouldn’t it be best for them to infect and keep the host alive rather than causing death? Do they just reproduce too much and kill the host without understanding that it would result in the host dying and themselves with it?

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21 Answers

Anonymous 0 Comments

IIRC the pathogens typically evolve to stay in a certain species with it staying alive. When it crosses into a different species with a less compatible immune system is when the death happens

Anonymous 0 Comments

It would be better, since there’d be a chance for a re-infection, and the host species generally won’t take extraordinary countermeasures. I mean, if you were a bug, you’d be better off being the common cold than Ebola. But the bugs don’t “understand” *anything* and they can’t adjust their effect.

What we see is evolution in action, as different strains compete — more infectious strains have a big advantage, while less lethal strains have a slight advantage.

Anonymous 0 Comments

IIRC the pathogens typically evolve to stay in a certain species with it staying alive. When it crosses into a different species with a less compatible immune system is when the death happens

Anonymous 0 Comments

>Do they just reproduce too much and kill the host without understanding that it would result in the host dying and themselves with it?

pretty much. bacteria, viruses, etc aren’t able to think or plan. They will go about their business as best they’re able to in the environment they’re in, and if that would result in killing the host there’s not really any way for them to stop themselves. A pathogen might gain a mutation that makes it more or less likely to kill its host. All else equal, being less lethal would make it better at reproducing, and over time mutations like that will stop the species from evolving to kill its host too quickly. However, evolution is really all about “good enough,” so as long as a pathogen isn’t *too* deadly to spread, it might stay that way.

Another factor is that microbes can affect different hosts in different ways. A microbe might be completely harmless in one species but deadly to another. In cases like that, it’s likely that the microbe is common enough in the species it’s harmless to that killing hosts of another species won’t hurt its chances very much. This general concept also applies to organisms that commonly live in soil or water and only sometimes infect animals, like tetanus or cholera. Other pathogens, like anthrax, can form spores that can survive and cause new infections long after the host dies, which also allows the species to survive even when quickly killing hosts.

Anonymous 0 Comments

IIRC the pathogens typically evolve to stay in a certain species with it staying alive. When it crosses into a different species with a less compatible immune system is when the death happens

Anonymous 0 Comments

It would be better, since there’d be a chance for a re-infection, and the host species generally won’t take extraordinary countermeasures. I mean, if you were a bug, you’d be better off being the common cold than Ebola. But the bugs don’t “understand” *anything* and they can’t adjust their effect.

What we see is evolution in action, as different strains compete — more infectious strains have a big advantage, while less lethal strains have a slight advantage.

Anonymous 0 Comments

It would be better, since there’d be a chance for a re-infection, and the host species generally won’t take extraordinary countermeasures. I mean, if you were a bug, you’d be better off being the common cold than Ebola. But the bugs don’t “understand” *anything* and they can’t adjust their effect.

What we see is evolution in action, as different strains compete — more infectious strains have a big advantage, while less lethal strains have a slight advantage.

Anonymous 0 Comments

>Do they just reproduce too much and kill the host without understanding that it would result in the host dying and themselves with it?

pretty much. bacteria, viruses, etc aren’t able to think or plan. They will go about their business as best they’re able to in the environment they’re in, and if that would result in killing the host there’s not really any way for them to stop themselves. A pathogen might gain a mutation that makes it more or less likely to kill its host. All else equal, being less lethal would make it better at reproducing, and over time mutations like that will stop the species from evolving to kill its host too quickly. However, evolution is really all about “good enough,” so as long as a pathogen isn’t *too* deadly to spread, it might stay that way.

Another factor is that microbes can affect different hosts in different ways. A microbe might be completely harmless in one species but deadly to another. In cases like that, it’s likely that the microbe is common enough in the species it’s harmless to that killing hosts of another species won’t hurt its chances very much. This general concept also applies to organisms that commonly live in soil or water and only sometimes infect animals, like tetanus or cholera. Other pathogens, like anthrax, can form spores that can survive and cause new infections long after the host dies, which also allows the species to survive even when quickly killing hosts.

Anonymous 0 Comments

>Do they just reproduce too much and kill the host without understanding that it would result in the host dying and themselves with it?

pretty much. bacteria, viruses, etc aren’t able to think or plan. They will go about their business as best they’re able to in the environment they’re in, and if that would result in killing the host there’s not really any way for them to stop themselves. A pathogen might gain a mutation that makes it more or less likely to kill its host. All else equal, being less lethal would make it better at reproducing, and over time mutations like that will stop the species from evolving to kill its host too quickly. However, evolution is really all about “good enough,” so as long as a pathogen isn’t *too* deadly to spread, it might stay that way.

Another factor is that microbes can affect different hosts in different ways. A microbe might be completely harmless in one species but deadly to another. In cases like that, it’s likely that the microbe is common enough in the species it’s harmless to that killing hosts of another species won’t hurt its chances very much. This general concept also applies to organisms that commonly live in soil or water and only sometimes infect animals, like tetanus or cholera. Other pathogens, like anthrax, can form spores that can survive and cause new infections long after the host dies, which also allows the species to survive even when quickly killing hosts.

Anonymous 0 Comments

>Do they just reproduce too much and kill the host without understanding
that it would result in the host dying and themselves with it?

They don’t understand anything, they’re not sentient.

They’re not trying to kill you, they’re just spreading. Turns out for a lot of microorganisms, the symptoms of them spreading will kill you.

And of course, in terms of evolution, it doesn’t matter if the pathogen kills you *after* you’ve already spread it.

But yes, there’s a reason the most deadly viruses don’t tend to spread as much as the less deadly ones. If a virus makes someone vomit blood and then die within a few days, people are going to stay away from them and it won’t spread very far.

If most people aren’t heavily affected by a virus, they’ll keep spreading it around. Even better if it’s mild enough that they carry on their day to day lives.

But they’re not intelligent. They can’t choose to do this.