Viruses are what viruses do, they don't have any of these properties that you could assign to them, they just do their thing (replicating using some combination of mechanisms provided by other organisms), and if they do it well they get to do it some more. There are no motivations, there is no plan, there is no function and they don't seek anything.
If they're too successful at what they do their host dies before they can be passed on, if they're not successful enough then the infection wave loses momentum and dies out. Effectively we have been helping them for the last year and a half do do this, without our help this particular virus would die out within a couple of weeks. It needs us for transportation and to be brought in contact with new viable hosts. On its own it can't do much of anything.
If they're too successful at what they do their host dies before they can be passed on, if they're not successful enough then the infection wave loses momentum and dies out. Effectively we have been helping them for the last year and a half do do this, without our help this particular virus would die out within a couple of weeks. It needs us for transportation and to be brought in contact with new viable hosts. On its own it can't do much of anything.