Dc ,he had fox lung worm and vet said he could have got it from eating something across the fields or got crap in his mouth when rolling in fox filth . I always did my best to keep him tip top and flea and worm him but went with what the vet prescribed back then thinking they new best but never again .
He was never one for slug,snail eating and I keep away from other dogs and parks etc ,apparently upto % of fox population as lungworm, poor sods . its a horrible thing .