The amphibian chytrid Batrachochytrium dendrobatidis occurs on freshwater shrimp in rain forest streams in Northern Queensland, Australia

Chytridiomycosis is a disease of amphibians caused by the chytrid fungus Batrachochytrium dendrobatidis. It can be highly virulent and is unusual in that it appears to drive many host species to local extinction during outbreaks. One mechanism that could facilitate this is the ability to grow saprophytically or on alternative hosts. This is common in other chytrids but has not been demonstrated for B. dendrobatidis in the field. B. dendrobatidis can grow on arthropod exoskeletons in the laboratory, and freshwater shrimp can be the most abundant animals in tropical rain forest streams. We therefore used diagnostic quantitative polymerase chain reaction to determine the infection status of freshwater shrimp from areas in which they are sympatric with frog species that have suffered declines in association with outbreaks of chytridiomycosis. We detected B. dendrobatidis on three individual shrimp belonging to two genera and collected from two widely separated streams. Two of the individuals had high levels of infection. This indicates that the presence of alternative hosts is likely to contribute to the extreme virulence of chytridiomycosis outbreaks in some systems. The presence of alternative hosts may allow B. dendrobatidis to remain in the environment after local extinctions of amphibian hosts, preventing the recovery of amphibian populations.