Doesn't have anything to do with summer, or salmon for that matter. Salmonids carry the fluke, even a good ol' rainbow will get'em sick. Remember, it's in the blood. Dogs can lick a fish all it wants, but it's injesting the blood that will bring on "salmon sickness". If it's going to be a fishing partner, you might as well get'em sick, treat it, and be good to go for the future. The trick is, you have to let them get quite sick, or they could get it again, BUT, as long as they get it good, you should be fine.

Take if from me, with a lab that literally lives on a hatchery, there is no 'avoiding' fish. He got sicker than all get out at around 6 months, and has never been ill since, even after eating daily morts, licking filleted carks, etc.