Characterization of a Novel Mesomycetozoean Infection (Dermotheca sp.) in a State-Endangered Salamander (Ambystoma platineum) and a Co-occurring Common Species (Ambystoma texanum)

Global amphibian declines have been attributed to anthropogenic factors and diseases including ranavirus and chytridiomycosis.1 Mesomycetozoean parasites (order Dermocystida) can cause direct mortality and thus may drive amphibian population declines, but their ecology and epidemiology remain understudied.2-6,8 Concerningly, these parasites have recently emerged in North American caudates, and studies on natural infections are important to determine their impact on threatened species.6 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 salamander health assessments were performed at six ephemeral wetlands in February and March 2016–2018. Beginning in 2017, single to multiple 1–3-mm raised, white, round to dumbbell-shaped skin nodules were identified in 24 silvery salamanders and two small-mouthed salamanders from five wetlands (prevalence=0–11.1. Histologic evaluation of skin biopsies (n=3) was consistent with dermocystid sporangia, and necropsies (n=2) confirmed that lesions were confined to the skin.7 Dermocystid 18S rRNA sequences (n=4) from both salamander species were identical. Phylogenetic analysis revealed a close relationship to Dermotheca [Amphibiocystidium] viridescens, a dermocystid affecting newts from the eastern United States.6 Dermocystids were not identified in silvery salamander 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. Further research is needed to determine the health effects and conservation implications of this parasite.