Print PageBatrachochytrium dendrobatidis (Bd) has been implicated in the decline or extinction of hundreds of amphibian species. Bd consumes keratin, which is found in tadpole mouthparts and the skin of juvenile and adult amphibians. Bd may be able to grow on alternative hosts that also contain keratin or keratin-like compounds. We investigated whether Bd could infect and maintain an infection in mosquito fish (Gambusia holbrooki) and crayfish (Procambarus acutus), which have keratin in their gastrointestinal tracts. Mosquito fish and crayfish were housed individually and exposed to Bd (or a Bd- control) for two weeks. They were then transferred to clean water for five weeks (with weekly water changes). All animals were euthanatized and swabbed in two locations: outer surface and inside the gastrointestinal tract.
Results/Conclusions
All mosquito fish survived to the end of the experiment and all of the swabs were negative for Bd. There was 50% mortality in the crayfish exposed to Bd, compared to 0% in the controls. All of the dead crayfish were positive for Bd and all the surviving crayfish had at least one Bd-positive swab (83% of the internal swabs and 50% of the external swabs were positive). In a separate experiment, crayfish that were initially positive for Bd based on external swabs had either cleared or considerably reduced the infections 10 weeks post-Bd exposure. Transmission experiments with amphibians and crayfish are underway. We also used qPCR to quantify Bd levels in frog-biting midges (Corethrella spp) collected from Gamboa, Panama. Ten percent were positive for Bd (20 flies total) and additional flies are presently being screened. This study indicates that there are non-amphibian hosts or vectors for Bd. Heterogeneity in the presence or densities of these hosts or vectors might help explain apparent geographic variation in rates of spread of Bd-related amphibian declines.
