If you fish much with your dogs its bests to let them get it. It takes about 3 days for it to show up. Call the vet and let them know that the dog got into some fish and they can tell you what to do. I used to duck hunt a lot and there was always dead fish around so when I got a new lab the first thing I did was let them chew on a fish. That way I knew when they got sick what it was. Once they get it chances are they will never get it again. I've been told they can never get it again, but I've also been told that different river systems carry different strains. I've never had a dog get it twice. The one I have now seems to be imune to it, she's licked the blood of many a fish and hasn't come down with it yet. I've had the pills for a couple of years waiting for her to get it.