I don't know anything about the Irish Guinefort, but I read the story
with a sense of deja vu, since it is an exact parallel of the Welsh
story of Beddgelert. This is a village in Wales - the name of which
means "grave of Gelert". The story is basically the same as "St.Dog",
but for snake, substitute wolf. [The Prince comes back to an empty
bloodstained cradle and assumed that his bloodstained hound,
Gelert, had eaten the child. After killing the dog the child is found
safe near the body of a wolf].
I know of no incidence of people connecting the site with healings,
though there is a, relatively modern, monument. And its a HUGE
tourist attraction. I'm quite sure that many people believe the story
implicitly, though there is no historical evidence.
I wonder if there are other European variants on the tale?
John Rylands University Library of Manchester