In situ treatment of juvenile frogs for disease can reverse population declines

Abstract

Effective management of wildlife populations threatened by disease requires accurate predictions about the consequences of intervention. However, generating such predictions is challenging, especially for organisms with complex life histories that are also threatened by climate change, such as montane amphibians. Cascades frogs (Rana cascadae) in northern California have experienced dramatic declines associated with the fungal pathogen Batrachochytrium dendrobatidis (Bd), and remnant populations are also threatened by changing climate conditions. We evaluated the population-level impacts of treating Cascades frog metamorphs with the antifungal chemical itraconazole using a field experiment and population simulations. We explored the influence of larval habitat on these treatment effects by including metamorphs from different larval habitat types. We found that frogs treated with itraconazole were more than four times more likely to survive their first winter than untreated controls and had reduced Bd infection intensity compared to other surviving frogs from the same cohort in the following year. We also found an effect of larval habitat type on Bd infection in recently metamorphosed frogs, with the lowest levels of infection occurring in frogs emerging from larval habitats that tend to be intermediate in temperature and drying rate. Applying the differential apparent overwinter survival of treated and untreated metamorphs to population projections suggests that intermittent antifungal treatment of metamorphs has the potential to restore population viability. Our results indicate that in situ treatment of individual hosts may be a useful component of a comprehensive management strategy to reduce the risk of pathogen-mediated population declines and extirpations.

Successful Drug-Mediated Host Clearance of Batrachochytrium salamandrivorans

“…Their protocol differed from ours in concentration (0.6 μg/mL), mode of application (spraying), duration (application 2×/d for 10 d) and husbandry conditions (no daily transfer to disinfected cages). Itraconazole has also been used for in situ mitigation of B. dendrobatidis , which increased population survival in the midterm ( 9 , 10 , 12 ). The exceptionally high levels of DNA copies we detected in some specimens along with severe skin lesions during the first days of treatment demonstrate that itraconazole is capable of effectively clearing even high infection loads of chytridiomycosis caused by B. salamandrivorans in S. salamandra salamanders ( 2 , 8 ) ( Figures 1 , 2 ).…”

“…Therefore, drug-mediated treatments can be critical in certain hosts. Furthermore, drug-based treatment protocols have been applied as viable mitigation strategies in wild amphibian populations ( 9 , 10 ).…”

Keeping the Heat On: Weighted Surveillance for Chytrid Fungus (Batrachochytrium Dendrobatidis) in Dixie Valley Toads (Anaxyrus [= Bufo] Williamsi)

“…If Bd is not present because it has not been introduced, continued surveillance for Bd and other novel, lethal pathogens is important to enable early intervention. To our knowledge, no rapid response plan exists for Dixie Valley toads should Bd be detected in Dixie Meadows, but management of Bd generally consists of controlling the spread of Bd , establishing assurance colonies, and preventing or treating chytridiomycosis (Woodhams et al 2011; Cook et al 2022; Knapp et al 2022). The lack of additional Dixie Valley toad populations means that the consequences of epidemic infection could be severe; careful monitoring and surveillance would be needed to enable early action to prevent declines and potential extinction of the species.…”

Frogs vs fungus: the emergence of amphibian chytridiomycosis

“…21 Targeted antifungal treatment of wild amphibians can reduce infection and increase survival. 22,23 However, as the fungus appears impossible to eradicate from the environment, antifungal treatment of wild amphibians only provides a short-term solution. Feasible, long-term solutions to combat chytridiomycosis are urgently required to prevent further loss of biodiversity.…”