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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>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.
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