The versions of the song that I came across were too 'witchy' and mysterious for me, until I found Colum's sensible and sensitive version.

Regarding the TB theory, anyone who's read the James Herriot books will realise the huge effort and expense that went into wiping out this curse. I remember , as a child, seeing large signs in meadows advertising "The Tuberculin Tested Herd....", so I'm ready to credit it as a plausible theory.