From the AmphibiaWeb site:
Although chytridiomycosis has devastated many amphibian populations worldwide, it remains unclear whether the fungal pathogen responsible (Batrachochytrium dendrobatidis) is a new emerging pathogen or an endemic pathogen which has been exacerbated by environmental changes.
A new paper in Ecology Letters by Walker et al. (2010) uses Bayesian modeling as well as genotyping to examines Bd on the Iberian peninsula, which was the site of the first European outbreak of chytridiomycosis. These authors conclude Bd is a novel pathogen in Iberia but that heterogeneity in population response is due to both biotic and abiotic factors.