Unravelling the disease ecology of Snake Fungal Disease: high genetic variability and ecological features of Ophidiomyces ophidiicola in Switzerland

The discovery of the fungal pathogen Ophidiomyces ophidiicola (Oo), the aetiologic agent of Snake Fungal Disease (SFD), has raised a growing interest in the North American and European scientific communities, in particular toward conservation. This pathogen is known or suspected to be associated with the declines of some snake populations in North America and was detected later in Europe. Its ecology, distribution and phylogeography still remain largely unknown. In this study, we collected skin swabs from 271 free-ranging snakes in Switzerland across 8 different species and 13 sites. The overall pathogen prevalence was at least 28% with sequences consistent with both the European and the North American lineages (respectively Clade I and II) of Oo. Semi-aquatic snakes were more likely to be infected by Oo, and high human disturbance (human frequentation and direct impact on snakes) was associated with a higher Oo prevalence, whereas season, body condition and snake species introduction was not. This study suggests that Switzerland might represent a region characterised by high genetic variability in Oo, and where long-term monitoring might be particularly important to follow the evolution of the disease in free-ranging snakes.