Emerging infectious diseases and amphibian population declines.

Emerging infectious diseases have been reported increasingly as causes of death in freeliving wild animals (1). These diseases are a particular threat to wildlife species whose population, habitat, or range has been diminished or artificially manipulated to promote species survival (e.g., captive breeding, translocation, and release programs) (2-4). An early example of an emerging disease panzootic was the introduction of rinderpest in African domestic cattle in 1889 (5). More recently, epizootics and panzootics of wildlife have been increasingly reported in terrestrial (1) and marine (6) habitats and are probably underreported (1,4,7-9). Recent advances in theoretical and experimental hostparasite ecology have demonstrated a major role for infectious agents in the population biology of wild animals (10,11). We discuss recent data on two newly emerging infectious diseases of amphibians and, by reference to host-parasite ecology, propose hypotheses to explain their origin and impact.