Lesion Severity and Associated Skin Health Parameters in Endangered Ozark Hellbender
Hardman, R. H., W. B. Sutton, K. J. Irwin, G. LeCleir, and D. L. Miller.  2019.  The 2019 Wildlife Disease Association International Conference, Tahoe City, CA, August 4-9, 2019.

Abstract:
The Ozark Hellbender, Cryptobranchus alleganiensis bishopi, is a federally endangered large aquatic salamander restricted to rivers within the Ozark Mountains. Arkansas populations have been reduced to a single river with minimal observed juvenile recruitment. Furthermore, over the past decade biologist have observed an increase of distal limb lesions with unknown etiology. We performed yearly surveys of C. a. bishopi in Arkansas during summers of 2011-2014, and recorded biometrics, obtained disease samples of a skin swab and tail punch biopsy as well as recorded both qualitative and quantitative details of lesions present. In 2014 we collected an additional dorsal skin swab for skin microbiome analysis. We performed qPCR to test for presence of Batrachochytrium dendrobatidis (Bd) from skin swabs and Ranavirus from tissue. From lesion data we developed a lesion scoring system from 0-7 and applied a lesion score to each hellbender blind of any other associated information. We performed linear mixed model regressions followed by AICc model evaluation to evaluate effects of pathogen infection status and individual biometrics on lesion score. From our microbiome swabs we performed 16S amplicon sequencing and calculated both Shannon Weiner Diversity and Bray Curtis Dissimilarity scores. We discovered 93.2% of all hellbenders had distal limb lesions characterized by digit swelling often progressing towards toe-tip ulceration. In severe cases we observed digital necrosis progressing to complete digit loss. Any recaptured individuals had the same or worse lesion score with an average score increase of 1 per year. The top predictive model for lesion severity included individual mass and Bd infection status with a significant, albeit weak, positive effect of Bd on lesion severity (β=0.87; C.I.: 0.11, 1.63). Microbiome results revealed decreased skin microbial community stability with increasing lesion score. Results demonstrate lesions are progressive, may be associated with overall skin health, and are likely multifactorial.