For me, it entirely depends on the location of where the mouse was caught. City vs Country.
In the city, you live in close proximity to other people, houses, and businesses all of which have a higher likelihood for opting for the mass baited poison traps instead of the "BAM" traps. Sorry, Emerilisms are addictive.
So theoretically a mouse that's just dined on some Poison a la Rat, and in a few hours could run into your home where he just can't help himself and gets caught in the traditional style trap, before letting the poison go to work.
In the country, I can't even SEE my nearest neighbor's house and the mouse would more than likely succumb to the poison before ever reacing inside my house to get caught in a trap.
So generally the mice I catch here at home, go in a baggie in the freezer for future use. To opt for as much safety as possible, I freeze them for 2 weeks to a month before ever considering using them, to make sure whatever parasites they might be harboring are rendered dead and harmless.
I don't use them as a sole source of my snakes' diet, I raise my own mice for that job. But I use them more as a scenting aid for a finicky eater or to perk up appetites after brumation or breeding. It seems my snake knows wild mouse from domestic, and just can't resist it...even males more interested in l'amour than food.
So if you live in the city or near enough to someone else where a mouse could make it to your house within a few hours of dining on poison, throw it out. If you're like me and live in the sticks, I use them occasionally.
In the course of two years of fecal tests, I've yet to have anything out of the ordinary show up. Maybe I'm just lucky, who knows. =)