EFFICACY OF SUBCUTANEOUS IMPLANTS TO PROVIDE CONTINUOUS PLASMA TERBINAFINE IN HELLBENDERS (CRYPTOBRANCHUS ALLEGANIENSI) FOR FUTURE PROPHYLACTIC USE AGAINST CHYTRIDIOMYCOSIS.

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.

GEOGRAPHIC AND INDIVIDUAL DETERMINANTS OF IMPORTANT AMPHIBIAN PATHOGENS IN HELLBENDERS (CRYPTOBRANCHUS ALLEGANIENSIS) IN TENNESSEE AND ARKANSAS, USA.

Wildlife diseases are a major threat for species conservation and there is a growing need to implement disease surveillance programs to protect species of concern. Globally, amphibian populations have suffered considerable losses from disease, particularly from chytrid fungi (Batrachochytrium dendrobatidis [Bd] and Batrachochytrium salamandrivorans [Bsal]) and ranavirus. Hellbenders (Cryptobranchus alleganiensis) are large riverine salamanders historically found throughout several watersheds of the eastern and midwestern US. Populations of both subspecies (Ozark hellbender, Cryptobranchus alleganiensis bishopi; eastern hellbender, Cryptobranchus alleganiensis alleganiensis) have experienced precipitous declines over at least the past five decades, and emerging pathogens are hypothesized to play a role. We surveyed Ozark hellbender populations in Arkansas (AR) and eastern hellbender populations in Middle Tennessee (MTN) and East Tennessee (ETN) for both chytrid fungi and ranavirus from swabs and tail tissue, respectively, from 2011 to 2017. Overall, we detected Bd on hellbenders from nine out of 15 rivers, with total prevalence of 26.7% (54/ 202) that varied regionally (AR: 33%, 28/86; MTN: 11%, 4/36; ETN: 28%, 22/80). Ranavirus prevalence (9.0%, 18/200) was comparatively lower than Bd, with less regional variation in prevalence (AR: 6%, 5/ 85; MTN: 11%, 4/36; ETN: 10%, 8/79). We did not detect Bsal in any hellbender populations. We detected a significant negative correlation between body condition score and probability of ranavirus infection (ß=-0.13, SE=0.06, 95% confidence interval: -0.24, -0.02). Evaluation of infection load of positive individuals revealed different trends than prevalence alone for both ranavirus and Bd, with MTN having a significantly greater average ranaviral load than both other regions. We documented a variety of lesions that likely have multiple etiologies on hellbenders located within all geographic regions. Our data represent a multiyear pathogen dataset across several regions of C. alleganiensis, and we emphasize the need for continued pathogen surveillance.