Electrolyte depletion and osmotic imbalance in amphibians with chytridiomycosis.
Mounting evidence implicates the disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis, in global amphibian declines and extinctions. While the virulence of this disease has been clearly demonstrated, there is, as yet, no mechanistic explanation for how B. dendrobatidis kills amphibians. To investigate the pathology of chytridiomycosis, blood samples were collected from uninfected, aclinically infected and clinically diseased amphibians and analyzed for a wide range of biochemical and hematological parameters. Here, we show that green tree frogs Litoria caerulea with severe chytridiomycosis had reduced plasma osmolality, sodium, potassium, magnesium and chloride concentrations. Stable plasma albumin, hematocrit and urea levels indicated that hydration status was unaffected, signifying depletion of electrolytes from circulation rather than dilution due to increased water uptake. We suggest that B. dendrobatidis kills amphibians by disrupting normal epidermal functioning, leading to osmotic imbalance through loss of electrolytes. Determining how B. dendrobatidis kills amphibians is fundamental to understanding the host-pathogen relationship and thus the population declines attributed to B. dendrobatidis. Understanding the mechanisms of mortality may also explain interspecific variation in susceptibility to chytridiomycosis.
Voyles
Jamie
J
Amphibian Disease Ecology Group, School of Public Health, Tropical Medicine and Rehabilitation Sciences, James Cook University, Townsville, Queensland 4811, Australia. jamie.voyles@jcu.edu.au
Berger
Lee
L
Young
Sam
S
Speare
Rick
R
Webb
Rebecca
R
Warner
Jeffrey
J
Rudd
Donna
D
Campbell
Ruth
R
Skerratt
Lee F
LF
D000818:Animals; D001001:Anura / Q000382:microbiology*; D001219:Aspartate Aminotransferases / Q000097:blood; D008411:Chytridiomycota / Q000472:pathogenicity*; D004573:Electrolytes / Q000097:blood*; D004906:Erythrocyte Count / Q000662:veterinary; D005969:Glutamate Dehydrogenase / Q000097:blood; D006400:Hematocrit / Q000662:veterinary; D054884:Host-Pathogen Interactions; D006863:Hydrogen-Ion Concentration; D009181:Mycoses / Q000150:complications / Q000503:physiopathology / Q000662:veterinary*; D009994:Osmolar Concentration; D012867:Skin / Q000382:microbiology; D013997:Time Factors; D014883:Water-Electrolyte Imbalance / Q000382:microbiology / Q000662:veterinary*
D004573:Electrolytes; D005969:Glutamate Dehydrogenase; D001219:Aspartate Aminotransferases