why do viruses try to kill the thing keeping them alive?
In: Biology
Virologist here just adding some clarification on some of the comments. Abnormally virulent viruses, like many of the ones that come from other animals and haven’t evolved to humans, will tend to evolve towards lower virulence because they’re causing too much harm to their hosts to transmit effectively or stably. BUT the opposite can also be true. Viruses need to exploit resources to facilitate their growth and cause symptoms (e.g., coughs) to promote transmission. Also, when viruses are competing with each other for hosts (as they often do in nature), generally the one that exploits its host faster and transmits before the host is incapacitated wins.
So viruses can evolve to be nicer to their hosts (see “avirulence hypothesis” – which is outdated but is still commonly taught to medical students and appears in a lot of these comments), or can evolve to be worse to their hosts. The balance between these two is the basis of the “virulence-transmission trade-off hypothesis”, which is the currently accepted theory of virulence evolution.
As an extra: while we often think that viruses that come to humans from other animals are more virulent, it’s entirely possible this is just detection bias. There could be constant zoonoses occurring that are sub-clinical that we don’t detect. It’s an ongoing area of research and our opinions are often coloured by decades of medical research that (quite rightly) focused its attention only on the worst of the worst of new diseases.
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