Characterization of Dermotheca sp. Infection in a midwestern state-endangered salamander (Ambystoma platineum) and a co-occurring common species (Ambystoma texanum)

Ichthyosporean parasites (order Dermocystida) can cause morbidity and mortality in amphibians, but their ecology and epidemiology remain understudied. We investigated the prevalence, gross and histologic appearance, and molecular phylogeny of a novel dermocystid in the state-endangered silvery salamander (Ambystoma platineum) and the co-occurring, non-threatened small-mouthed salamander (Ambystoma texanum) from Illinois. Silvery salamanders (N = 610) were sampled at six ephemeral wetlands from 2016 to 2018. Beginning in 2017, 1–3 mm raised, white skin nodules were identified in 24 silvery salamanders and two small-mouthed salamanders from five wetlands (prevalence = 0–11.1%). Skin biopsy histology (N = 4) was consistent with dermocystid sporangia, and necropsies (N = 3) identified infrequent hepatic sporangia. Parasitic 18S rRNA sequences (N = 5) from both salamander species were identical, and phylogenetic analysis revealed a close relationship to Dermotheca viridescens. Dermocystids were not identified in museum specimens from the same wetlands (N = 125) dating back to 1973. This is the first report of Dermotheca sp. affecting caudates in the Midwestern United States. Future research is needed to determine the effects of this pathogen on individual and population health, and to assess whether this organism poses a threat to the conservation of ambystomatid salamanders.