Detection of Batrachochytrium dendrobatidis ( Bd ) and chytridiomycosis. (A) infectious Bd zoospore 1000 × magnification stained with congo red. Infectious zoospores in the environment [20, 229–231] or in association with amphibian skin may meet with host resistance mechanisms such as mucosal antibodies, antimicrobial skin peptides, or mutualistic bacteria [61, 127, 180, 205]. (B) Small rod-shaped bacteria associated with sloughed skin from Rana muscosa are stained red with propidium iodide. Larger Bd zoosporangia are stained blue with calcofluor white. (C) Bd infecting frog skin 1000 × magnification stained with calcofluor white and propidium iodide. (D) A healthy infected frog, Pelophylax lessonae. (E) A diseased frog with chytridiomycosis. Note the skin shedding in water and splayed legs. If keratinized cells become infected, infections may be controlled by host responses that reduce Bd population growth resulting in host tolerance of low-intensity infection and no clinical signs of disease, as in (D). An alternative outcome of infection is uncontrolled Bd growth that leads to clinical chytridiomycosis (Figure 2E; reviewed in ). A simple definition of disease is uncontrolled infection.