[ars]

> But what if a mutation occurs that results in it becoming a deadly disease

It seems dangerous to me as well, but I should point out that viruses don't typically do that - they are either dangerous or not. They might change how infectious, or which species they target, but it rare to go from harmless to dangerous.

It's also not in their interest to be dangerous, it's better for them to simply be infectious without causing serious illness.

[abandonliberty]

You're right, Some of the most evolutionary fit viruses are the HERVs.[1]

Unfortunately viruses (and genes for that matter) don't mutate intentionally for their best interests.

[1]https://en.wikipedia.org/wiki/Endogenous_retrovirus

[task_queue]

Cancer is not in an organism's interest, but mutations can still occur and cause it.