Chytridiomycosis, caused by chytrid fungus, has driven the most devastating vertebrate disease event in recorded history, causing mass amphibian die-offs on every inhabited continent.
Amphibians dying from chytridiomycosis experience progressive loss of skin function, leading to electrolyte imbalance and ultimately cardiac arrest over days to weeks. The disease causes lethargy, abnormal posture, and skin sloughing as it progresses. Individual frogs, toads, and salamanders die in significant numbers — die-offs kill thousands of individuals at stream sites where previously hundreds or thousands of individuals gathered to breed. The global scale of the crisis represents one of the largest individual animal welfare emergencies caused by an infectious disease.