Amphibian declines: an immunological perspective

Many, but not all, amphibian populations have been declining on all six con tinents on which they live. Although habitat destruction, direct applicatio n of toxicants, and introduction of predators/competitors are obvious cause s of amphibian declines, many amphibians are dying of infectious diseases i n relatively pristine habitats on several continents. In this paper, we rev iew the patterns of these disease outbreaks and the characteristics of amph ibian immune systems. Hypotheses are presented to explain the apparent susc eptibility of amphibians to these pathogens. Natural and man-made factors t hat can alter amphibian immune responses to pathogens are discussed. Additi onal research is needed on the biology of the specific pathogens, the patte rn of immune responses they elicit, and the nature of environmental stresso rs that may increase susceptibility to infectious disease. (C) 1999 Elsevie r Science Ltd. All rights reserved.