Detection of spatiotemporal variation in Ranavirus distribution using eDNA

Amphibian population declines have been associated with emerging diseases
including ranaviruses, which can cause mass die-offs across entire
amphibian communities. Understanding and mitigating disease spread
requires knowledge of spatial and temporal patterns of pathogen
distribution, but also how environmental factors influence pathogen
occurrence. We applied environmental DNA (eDNA) detection tools to survey
spatial and temporal distributions of ranaviruses by sampling 103
waterbodies in southeastern Ontario, Canada, and assessed the role of
abiotic factors as predictors of pathogen occurrence. Ten waterbodies
sampled during June-August (>30 km between sites) revealed that
ranavirus was marginally more prevalent (p = 0.055) during the latter part
of the summer. Ninety-three sites sampled at a finer scale (<10km
between sites) exhibited seasonal variability in ranavirus detection (site
prevalence: 56% May; 66% July). Occupancy modeling revealed that wetland
size and elevation influenced ranavirus occurrence while sampling date and
water temperature influenced probability of detection. These findings
indicate that biotic factors, such as host density and alternative hosts,
should be investigated further as likely determinants of ranavirus
prevalence across the landscape. Further, these results highlight the
sensitivity of eDNA for detecting widespread presence of ranavirus, and
that abiotic factors may have a limited role in determining its prevalence
and infectivity.