The pathology of Bsal chytridiomycosis: documenting anatomical changes and exploring what they might mean clinically
Miller, D. L., A. K. Grzelak, A. E. Towe, R. Ossiboff, C. Cray, R. Kumar, K. Ash, E. D. Carter, B. A. Bajo, M. Bohanon, A. C. Peterson, and M. J. Gray.  2019.  Joint Meeting of the American Fisheries Society and The Wildlife Society, Reno, NV, September, 2019.  (invited)

Abstract:
Batrachochytrium salamandrivorans (Bsal) is a recently discovered pathogen that is of global concern because of its potential to cause high mortality in amphibians, especially salamander species. Experimental challenges are underway to estimate species susceptibilities in order to understand invasion risk and develop disease mitigation strategies to minimize the possibility of Bsal emerging in North America. To date, 29 amphibian species (22 salamander and 7 anuran) have been tested. For each challenge, individuals were exposed to Bsal in a water bath at one of five concentrations (0, 5 x 103, 104, 105, 106) for 24 hours, and their condition monitored for six weeks. Gross changes varied from increased skin sloughing to discrete ulcerations. Histologically, Bsal organisms were seen from superficial to full thickness epidermis, and in discrete crater formations or diffuse laminar patterns. These changes were seen in species of salamanders and anurans. For a similar fungus, B. dendrobatidis (Bd), changes in blood electrolytes that lead to host paralysis and cardiac arrest have been reported. Therefore, we hypothesized that species experiencing Bsal chytridiomycosis would have similar changes in electrolytes, because like Bd, Bsal damages the epidermis hence may affect skin osmoregulation – a key physiological process that influences blood chemistry. To test this hypothesis, we collected blood from the hearts of a larger susceptible species, Taricha granulosa, at necropsy using heparinized capillary tubes. A blood smear was prepared, and a portion of whole blood was added to Natt Herrick’s solution for total blood cell counts. The remaining blood was centrifuged and plasma collected for blood chemistry profiles and protein electrophoresis. Initial biochemical results revealed decreases in sodium, chloride, and potassium in terminal stages of the disease (5x106 dose) similar to Bd. Identifying biochemical changes associated with Bsal chytridiomycosis will help elucidate pathogenesis and be key to developing disease mitigation strategies and exploring treatment options in susceptible species.