Re: HOLY "s" I have aspergillus fumigatatus/aspergillus niger!!
Cardboard walls, ancient carpeting, and crap heating ducts? SURE. But other than the cardboard walls, everything can be torn out at low-to-no cost.
Concrete walls? Rip off whatever's on them, paint the hell out of them and you're done (been doing that recently myself, to great effect). Floors? Rip'em out, toss down some plastic linoleum if you're broke or something better if you have the cash - done.
...As to ducts, if you're thinking they are at fault, JUST SEAL THEM. Hell, weld 'em shut if you're feeling especially nervous.
...vehicles, though?! Ain't nothing but upholstery that can possibly get messed up in a vehicle, and that's easily replaceable. Well, ok, there's also the A/C system, but it's rather small and simple compared to a house's ducts - hell, you can just install an aftermarket A/C, brand new, for a grand. Or you can act like you don't have an A/C and use the windows.