The emerging amphibian pathogen Batrachochytrium dendrobatidis globally infects introduced populations of the North American bullfrog, Rana catesbeiana

Abstract

Batrachochytrium dendrobatidis is the chytridiomycete fungus which has been implicated in global amphibian declines and numerous species extinctions. Here, we show that introduced North American bullfrogs (Rana catesbeiana) consistently carry this emerging pathogenic fungus. We detected infections by this fungus on introduced bullfrogs from seven of eight countries using both PCR and microscopic techniques. Only native bullfrogs from eastern Canada and introduced bullfrogs from Japan showed no sign of infection. The bullfrog is the most commonly farmed amphibian, and escapes and subsequent establishment of feral populations regularly occur. These factors taken together with our study suggest that the global threat of B. dendrobatidis disease transmission posed by bullfrogs is significant.

Figure 1

Histological evidence of Batrachochytrium dendrobatidis infection in a South American bullfrog. Multiple empty intracellular zoosporangia (sub-oval white structures) can be seen within the superficial, keratinized, layer of the epidermis. (a) A sporangium containing zoospores (arrow); (b) an empty zoosporangium with its discharge papilla clearly visible (arrow).