Does Chytridiomycosis Disrupt Amphibian Skin Function?

Chytridiomycosis, a disease caused by the fungus Batrachochytrium dendrobatidis (Bd), potentially disrupts osmoregulation or respiration across the skin of amphibians it infects, releases toxins into the host, or both. We investigated whether infection with Bd alters water balance or metabolic rate of the hylid frog Litoria raniformis. Frogs were held in laboratory conditions simulating those in which Bd epizootics had been observed in the field. We inoculated six frogs with infective Bd zoospores, held the subjects in individual containers, and compared their course of infection and associated physiological measures with those of six controls. Experimental subjects exhibited clinical signs of chytridiomycosis during the early period of infection, one week after they were inoculated, possibly due to invasion of Bd into the skin. These clinical signs were accompanied by significant inhibition of rehydration through the skin. However, we detected no changes in metabolic rate attributable to chytridiomycosis after one week. Five months after inoculation, all but one of the infected subjects had survived. Molecular testing confirmed that surviving frogs, although aclinical, still were infected. Control and infected subjects showed no difference in water balance or metabolism. These results provide evidence of inhibited rehydration in individuals exhibiting clinical signs of chytridiomycosis. However, aclinical chytridiomycosis does not severely affect amphibian skin function. Frogs that survive infection by Bd, even if they remain infected, may suffer no significant impairment in their physiological responses. The disease progression, with initial clinical signs of chytridiomycosis followed by apparent full recovery, is consistent with an adaptive immune response to Bd infection. Further research is needed to determine how Bd causes clinical chytridiomycosis and the immunological mechanisms by which hosts respond to Bd.