One of the most proposed causes for the declining amphibian populations has been the disease chytridiomycosis, which is caused by the skin infection by the fungus Batrachochytrium dendrobatidis. Although evidence for some populations linking the decline with the fungus has been limited, the mechanism by which the disease may kill the frogs was unknown, until now. A group of researchers from Australia and United States have published a paper in Science indicating that the fungus inhibits the transport of electrolytes, which ends up killing the frog.
Further studies should confirm and refine their findings.
Jamie Voyles, Sam Young, Lee Berger, Craig Campbell, Wyatt F. Voyles, Anuwat Dinudom, David Cook, Rebecca Webb, Ross A. Alford, Lee F. Skerratt, and Rick Speare. 2009. Pathogenesis of Chytridiomycosis, a Cause of Catastrophic Amphibian Declines. Science 326: 582. DOI: 10.1126/science.1176765.