"Streets of Laredo" and "St. James Infirmary" are closely related, sharing the same old-world antecedents. Here's an interesting article on this topic from this week's New Orleans Gambit Weekly:

http://www.bestofneworleans.com/dispatch/current/cover_story.php

(This link, of course, will probably expire at some point. Posted, and currently avialable, on June 16, 2005.)