Why would it not be? It's like the distinction between "a crocodile" and "being mauled" or "a credit card" and "crippling debt"; while they may frequently co-occur, either can exist without the other. Further, recognizing that they are distinct allows you to build causal models, which are vital to taking productive action.
Various other viral (and even less commonly, microbial) challenges, though it's rare. HIV is special in this regard because it's the only example (so far as I know) that's transmissible.
