Epidermal Trauma Reduces the Impact of Batrachochytrium dendrobatidis in Fowler's Toads (Anaxyrus fowleri)

The amphibian epidermis presents many barriers that prevent pathogen infection. Much effort has been placed on examining determinants of infectivity and pathogenicity of Batrachochytrium dendrobatidis (Bd) in amphibians. How- ever, no research has examined how trauma to the epidermis can affect susceptibility to and virulence of Bd infections in amphibians. Trauma is a common entry point for secondary infections that would otherwise be immunologically defensi- ble to a host. The objective of our study was to determine if epidermal trauma would impact the outcome of Bd exposure. We predicted that epidermal trauma would make amphibians more susceptible to infection and result in more virulent in- fections. To test this prediction we compared susceptibility to infection, mortality, and survival time among three groups of Fowler's Toads, Anaxyrus fowleri (Hinckley); trauma and Bd, Bd only, and no Bd. Counter to our predictions we found that, with reference to negative controls, epidermal trauma and Bd together reduced susceptibility to infection, reduced overall mortality, and increased survival time compared to toads exposed to Bd only. Epidermal trauma is commonplace for wild amphibians, and is caused by predation attempts, combat, and unfavorable environmental conditions. We suggest that trauma to the epidermis preceding exposure to Batrachochytrium dendrobatidis elicits an innate immune response not initiated by the pathogen alone. Our data suggest that trauma could temporarily reduce susceptibility to, and virulence of, Batrachochytrium dendrobatidis infections of amphibians.