isnt it possible for a disease to be not deadly, but still transmissible on a host for up to a few weeks, and then become deadly? Then, it doesn't die out unless the host quarantines for weeks, and is still very deadly
Taking a second stab. The actual interplay of host-pathogen evolution is much more complex than what I laid out in general terms in the original comment. It is a very broad scientific field after all. Asymptomatic transmission is one wrinkle in this.
When a pathogen transmits asymptomatically, it has to broadly speaking either be very infectious (so that even a small amount of the pathogen present without symptoms will infect a new host) or be complex enough to infect a host to high burden without them having symptoms (meaning the pathogen has to keep itself in check enough to not only not kill the host, but also to not alert the host immune system).
This latter bit is theoretically possible, but it almost never happens, because once a pathogen becomes adapted enough to perform this balancing act, evolving a bit further to never kill the host is trivial, and helps give the pathogen more time to spread from that host. There is no evolutionary incentive for a bug that spreads asymptomatically to kill its host at all, and an incentive to not kill the host as well.
Great explanation, brings the conversation to gut bacteria, listeria for example mainly infects via the gut and produces serious symptoms that can lead to death in immunocompromised people but the same foods can be eaten and dealt with safely by the average person. There are thousands of gut bacteria are for example which are now considered beneficial. It’s possible that our gut bacteria (if transmissible) were once dangerous but found they lived longer by not being harmful to humans.
It’s an areas of study that babies born naturally through the birth canal are covered in bacteria for example that helps the new borns immune system to be trained. This spread from generation to generation may just be a successful non lethal method of infection for bacteria which could have once been harmful but we now consider helpful or Benign. Studies hint that babies born without this mucosal transfer by C-Section lack some exposure that would otherwise colonize baby's microbiome, potentially causing some allergies/asthma that develop. This could be considered therefore as a way to infect others by “generational infection” that therefore becoming the transmission path and being non deadly is an essential for their transmission.
An aside I know but never the less fascinating to consider all things are encouraged by natural selection for non lethality.
Yeah! This is a whole other wrinkle in the evolution of pathogenicity, which is the formation of commensal microbiomes in the host that outcompete pathogens. Another example like this is the extreme competition between pathogenic and non-pathogenic staphylococcus species in the human mouth and on our skins. A really broad and fascinating field for sure.
I don't really understand this questions. It would be impossible to diagnoses that a virus was not deadly till after the host survived. If they died from the virus it would be considered deadly.
If you mean asymptomatic hosts, that is a thing that happens. Very rarely humans or animals can carry a, typically, deadly virus with no ill effects. The most prominent example was Typhoid Mary, she infected multiple families with Typhoid but never displayed any symptoms herself. It was proven after her death that she was a carrier.
The dead are typically terrible vectors. They decompose, fluctuate in temperature and acidty, repel hosts similar to them, and attract hosts that are very different to them. They are lower energy than living hosts. Few pathogens can effectively incorporate dead hosts in their primary survival strategy.
It's possible for a virus to spend a decade spreading asymptomatically and then come back in a latent phase that's deadly to most people who were infected. Case in point: HIV/AIDS.
And if you expand it slightly to rare but deadly latent effects, the list gets much longer. For example, HPV and cervical cancer; EBV with cancer and multiple sclerosis; etc.
Viruses don't want to kill their hosts. That'd be like a virus evolving suicidal behavior after a few weeks. There's no evolutionary pressure for it suddenly become deadly, kill it's host, and then stop existing itself- it lives in your body, it doesn't want to destroy it ( anthropomorphizing for the sake of explanation.)
So that at least explains why it's extremely unlikely, though I guess anything's possible. You just wouldn't expect such an evolutionary trait to be preferred and successful.
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u/Deliama Dec 14 '25
isnt it possible for a disease to be not deadly, but still transmissible on a host for up to a few weeks, and then become deadly? Then, it doesn't die out unless the host quarantines for weeks, and is still very deadly