I'm sorry to hear about your bout with lung worm. Isn't it amazing a parasite that usually infects hoses and cattle can affect such a small animal. My great dane actually once had a bout with lung worm but after a couple rounds of panacure he was better but with some residual lung damage that made him continue to cough until he passed of degeneritive cardio myopthy. I'm sure some of the coughing at that point could have been contributed to the heart ailment but there was damage from the long term undiagnosed lungworm. Like you said, cysts aren't shed in every fecal, and it is very difficult to catch them, much like giardia and coccidia, but thankfully (in mammals anyway) treatment is usually effective and reasonable.