It\'s bothered me for a while now. I understand why a parasitoid would do this,

Question

It's bothered me for a while now. I understand why a parasitoid would do this, as it only temporarily requires the host, and that not all parasites kill their hosts.

There seems to be no evolutionary advantage in killing a host, because the parasite relies on the host for resources. Yet some organisms, usually microscopic pathogens, seem to fatally damage the host with no immediate benefit to themselves. Why is this?

I know this is asking for a broad soft answer, but I don't want the question to get bogged down by a specific species, although bonus points for using examples.

Explanation / Answer

I can think of several (non-exclusive and non-exhaustive) hypotheses:

Maladptive. It is maladaptive. Because it is a new virus coming from another species or because it is not adapted to our modern lifespan.

Benefit of the host immune system to the parasite. Some parasites might benefit from host immune defense (sneezing helps bacteria to spread) and death is a consequence of the selection for increasing disease symptomes to the host.

Pathogen's and host's fate. The pathogen's fate is not linked to the host's fate. This is espacially true if the pathogens spread well (easily jump from one host to another) I guess or for parasito

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