Personally, I am convinced this happens (based on my own 3-year experience with the same parasite strain) but I haven't found it in literature for any helminth.
The LE strain of "Schistosoma mansoni" has been maintained, at UFMG (Brazil), by successive passages between "Biomphalaria glabrata" and hamsters during about 50 years. The cercaria infectivitvity is so far OK. I don´t know the parasite species that you have worked, however this information, perhaps, can be helpful for you to think about your question.
Dear Raad, thank you for interesting links. Nevetheless, what I search is an example of cercariae attenuated without any chemicals, i.e. just by lab passaging.