[totalZero]

The counterexample to this line of thinking is a lethal virus with a lengthy incubation period that can transmit while the host is asymptomatic.

[pasquinelli]

That's the history of syphilis if i understand correctly. It started out as a serious plague that covered its host in oozing sores and killed them in a couple months, now its symptoms are much less severe and it kills in a matter of decades.

[fxj]

You just described HIV.