Amphibian chytridiomycosis, emerging diseases and pathogen pollution

Peter Daszak¹, Andrew A. Cunningham² & Alex D. Hyatt³

¹ Institute of Ecology, University of Georgia, Athens GA 30602, USA
² Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK
³ Australian Animal Health Lab, CSIRO, Port Arlington Road, Geelong, Australia, 3022

Amphibian chytridiomycosis is an emerging disease of panzootic proportions. Emerging infectious diseases (EIDs) are defined as diseases that have recently increased in incidence or geographic range, infected new host species or populations, are caused by recently evolved pathogens or are newly recognized. The recent, striking chytridiomycosis-associated amphibian mass mortality in Australia, Central and North America and the lack of presence of Batrachochytrium in archived specimens from these areas prior to the 1970s suggest that chytridiomycosis fits the EID profile. EIDs are a widely recognized phenomenon in humans, from A.I.D.S to re-emerging tuberculosis, drug-resistant microbes and Ebola virus. In this presentation, we will demonstrate that chytridiomycosis is a prime example in a growing cohort of wildlife EIDs, many of which threaten biodiversity on a panglobal scale. Human EIDs are driven to emerge by a range of ecological changes associated with globalization (increased human transport, increased global trade, urbanization). The causal factors driving wildlife EIDs are also predominantly anthropogenic and largely due to the movement of hosts and/or pathogens at an unprecedented scale ("pathogen pollution"). What factors have driven the emergence of amphibian chytridiomycosis? Our analysis of the available data suggest two potential causes of emergence - introduction and climate change - acting independently, or in consort with each other or a range of unknown factors. One of the striking features of chytridiomycosis is its association with local (population) extinction. We will hypothesize, with reference to our knowledge of the biology of Batrachochytrium, that this pathogen is able to avoid its own extinction as it moves into and decimates a population by aclinical infection of tadpoles and/or survival as a saprobe (outside the amphibian host). As our knowledge of the epizootiology and biology of chytridiomycosis increases, we will be able to test these hypotheses and greater understand the origins and impact of this devastating infection.