The Old World would be Europe, Africa, and Asia. The term is based on European perceptions of the world around starting with Columbus' "discovery" of the New World (the Americas). I believe Australasia is also considered the Old World as well.

Chytridiomycosis effects salamanders as well, though it is more widely known amongst frogs, which out-number all other amphibian orders and are not as secretive as the other two amphibian orders, Caudata amd Gymnophonia.