COS 259-3 - Unravelling the contribution of host species and pathogen identity on the broad geographical disease patterns of an emerging wildlife disease, snake fungal disease

Abstract: Infectious diseases are influenced by interactions between hosts and pathogens in variable environments and are rarely homogenous across the landscape. Areas with elevated disease incidence maintain a high force of infection, facilitate pathogen spread, and may signify areas with impacts to host populations. However, isolating processes that result in increases in infection prevalence and intensity remains a challenge. Here we elucidate the contribution of pathogen genotype and host species in disease hotspots of Ophidiomyces ophidiicola, the pathogen that causes snake fungal disease, in 21 species of snakes across 10 countries in Europe. We found isolated areas of disease hotspots across several regions in Europe where infections were otherwise low. We performed genotyping analyses on extracted DNA from 93 samples and described the presence of four pathogen genotypes across the landscape, including two that were identical to ITS2 region sequences of strains previously described in the USA. Our analyses revealed significant differences in infection based on host species and pathogen genotype. Over 80% of positive detections were from host species in the Natrix genus, indicating potentially higher susceptibility in this group. Pathogen genotype had important effects on transmission, and areas with multiple pathogen genotypes had higher host infection prevalence. Follow up experimental investigation revealed that pathogen genotypes associated with higher disease incidence also had higher pathogen virulence. However, one species, N. tessellata, appeared highly susceptible, showing increased infection prevalence regardless of pathogen genotype and indicating that this species may be important in pathogen maintenance. In addition, we identified a new genotype not previously described in Europe. This genotype shows higher virulence than other strains in circulation but is currently highly localized, drawing attention to implications for snake conservation in this region. More broadly, our findings demonstrate that coevolutionary relationships between hosts and pathogens may be key mechanisms in explaining patterns of disease prevalence across broad geographical scales.