The aggressiveness can be really very high, Ebola Zaire
> for example kills 9 out of 10 human hosts in <14 days. I'd speculated that,
> for the virus, this is not too good an idea as if you want to spread your
> genetic material if your are too pathogenic then you eventually loose your
> host. Whereas AIDS although equally agressive allows the host to live thus
> allowing its (somewhat rapid) propagation.
>True, probably the most successful virus would be one that could replicate
without causing any pathogenesis. Who knows perhaps we are infected with
many more viruses than we know.