Doctoral Dissertations

Date of Award

5-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Comparative and Experimental Medicine

Major Professor

Debra L. Miller

Committee Members

Mark Q. Wilber, Sreekmari Rajeev, Rebecca Hardman

Abstract

Chytridiomycosis, a cutaneous fungal disease caused by two related fungi, Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal), is a major cause of amphibian population declines worldwide. Bd has a broad distribution, covering every continent except for Antarctica. Meanwhile, Bsal is currently restricted to Europe and Asia. Treatment options for both Bd and Bsal remain a major area of concern for wild populations. Recently, implants for long-term, parenteral antifungal drug administration have shown some promise in fungal diseases in wildlife. We investigated the safety and efficacy of an intracoelomic implant of the antifungal drug terbinafine in greater sirens exposed to Bd. While the efficacy results were inconclusive, the implants did not cause harm and led to detectable levels of terbinafine in plasma. The use of such implants in amphibians remains an important area for further investigation. In a separate study, we explored the use of a probiotic bacteria and addition of a known secondary bacterial pathogen in Bsal-infected animals. The objectives of this study were to determine the safety and efficacy of using probiotic bacteria to prevent and treat Bsal chytridiomycosis, and to evaluate bacteremia and septicemia as components of morbidity and mortality in animals that succumb to disease. While the probiotic treatment did not impact mortality rates, there was evidence of bacterial infiltration into the blood and organs in Bsal-exposed animals. Finally, while there is an ever-growing body of research elucidating the acute impacts of Bsal, sublethal effects on population dynamics must be considered as well. We used a two-part study design to investigate the impacts of Bsal exposure on individual reproductive potential, and on reproductive success under breeding conditions. This study provided evidence for terminal investment, increased reproductive effort in the face of pathogen exposure, in eastern newts exposed to Bsal. Overall, the findings of this research provide more information about new avenues for treatment for chytridiomycosis and their potential drawbacks, and expand on the existing knowledge of Bsal pathogenesis. These findings will provide a foundation for future amphibian disease research, informing mitigation efforts for this disease in managed and free-ranging amphibian populations.

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