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EFFICACY OF SUBCUTANEOUS IMPLANTS TO PROVIDE CONTINUOUS PLASMA TERBINAFINE IN HELLBENDERS (CRYPTOBRANCHUS
Rebecca H Hardman1,2, Sherry Cox2, Sherri Doro Reinsch3
1Center For Wildlife Health, Joe Johnson Boulevard, University of Tennessee, Knoxville, TN 37996, USA, lavalizard17@gmail.com.
Abstract:
Batrachochytrium dendrobatidis (Bd) is an important fungal pathogen present in wild hellbender (Cryptobranchus alleganiensis) populations that appears to cause disease during novel exposure and acute stress. Hellbender repatriation efforts are ongoing to combat declining populations, but mortality by chytridiomycosis (disease from Bd) after release has been reported. The goal was to determine whether a safe antifungal agent could be administered and provide prolonged plasma concentrations without repeated handling. A subcutaneous implant impregnated with 24.5 mg of terbinafine was tested in three juvenile eastern hellbenders (C. a. alleganiensis) raised in human care, and plasma terbinafine concentrations were recorded from weekly to biweekly for 141 days. Plasma concentrations were variable, with peak plasma concentrations of 1,610, 112, and 66 ng/ml between 28 and 56 days postimplant. Although all hellbenders achieved plasma concentrations above the published minimum inhibitory concentration for terbinafine against Bd zoospores (63 ng/ml) at several time points, only one individual remained above this threshold for more than two consecutive time intervals. Results show the potential for these implants as a prophylaxis for chytridiomycosis in captive-to-wild hellbender releases. However, further investigation will be needed to determine the plasma concentrations required to achieve prophylaxis in vivo and implant reliability.
Insights
Subcutaneous terbinafine implants show potential for preventing chytridiomycosis in hellbenders during repatriation. Further research is needed to confirm efficacy and implant reliability for long-term protection against Batrachochytrium dendrobatidis.
Area of Science:
- Amphibian conservation
- Veterinary medicine
- Mycology
Background:
- Batrachochytrium dendrobatidis (Bd) causes chytridiomycosis, a significant threat to wild hellbender (Cryptobranchus alleganiensis) populations.
- Mortality in reintroduced hellbenders due to Bd infection necessitates effective prophylactic treatments.
- Current treatment methods require repeated handling, which can cause stress and be impractical for wild populations.
Purpose of the Study:
- To evaluate the feasibility of using subcutaneous terbinafine implants for sustained antifungal drug delivery in hellbenders.
- To determine if terbinafine implants can achieve and maintain plasma concentrations above the minimum inhibitory concentration for Bd.
- To assess the duration of therapeutic terbinafine plasma concentrations following a single implant administration.
Main Methods:
- Three juvenile eastern hellbenders (C. a. alleganiensis) received a 24.5 mg terbinafine subcutaneous implant.
- Plasma terbinafine concentrations were monitored weekly to biweekly for 141 days post-implantation.
- Concentrations were compared against the published minimum inhibitory concentration (MIC) of 63 ng/ml for Bd zoospores.
Main Results:
- Plasma terbinafine concentrations were highly variable among individuals and over time.
- Peak concentrations ranged from 66 to 1,610 ng/ml, occurring between 28 and 56 days post-implantation.
- All hellbenders reached concentrations above the Bd MIC, but only one maintained levels above 63 ng/ml for more than two consecutive sampling intervals.
Conclusions:
- Terbinafine implants offer a potential method for prophylaxis against chytridiomycosis in hellbenders before release into the wild.
- The variable and transient nature of plasma concentrations suggests a need for further optimization.
- Additional research is required to establish effective in vivo concentrations for prophylaxis and assess long-term implant performance and reliability.
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