How can environmental fecal sampling support Echinococcus multilocularis surveillance in wild carnivores?

Foxes (Vulpes vulpes) and raccoon dogs (Nyctereutes procyonoides) are natural definitive hosts of Echinococcus multilocularis. The aim of this study was to compare E. multilocularis findings from the necropsy analysis of hunted animals with those from environmental fecal samples. Between November 2023 and March 2025, 84 carcasses (58 foxes, 26 raccoon dogs) were provided by volunteer hunters located in the area of two municipalities of the island Rügen in North-Eastern Germany. Analysis using the sedimentation counting technique and real-time PCR resulted in a combined positive detection of E. multilocularis in 37.9% (95% Confidence interval [CI] 25.5-51.6%) of foxes and in 15.4% (95% CI 4.4-34.9%) of raccoon dogs. Between February and April 2025, during 13 excursions in the same two municipalities, two-person teams collected 365 environmental fecal samples, which were targeted to be from foxes and raccoon dogs. Species identification through species-specific real-time PCR revealed that the fecal samples were from foxes (56.2%), raccoon dogs (2.7%), domestic dogs or wolves (9.0%), domestic cats or wildcats (0.6%), raccoons (0.3%), and unknown species (26.0%). E. multilocularis DNA was detected by real-time PCR in 18.1% (95% CI 13.1-24.1%) of fox and in 10.0% (95% CI, 0.3-44.5%) of raccoon dog feces. The examination of environmental fecal samples for E. multilocularis appeared to be less sensitive compared to the analysis of necropsy samples from hunted foxes and raccoon dogs. The lower proportion of E. multilocularis DNA in environmental fecal samples may be due to adverse environmental factors, such as degradation by UV light or leaching from precipitation. Nevertheless, environmental fecal sample collection was less labor-intensive and time-consuming and was able to confirm the presence of E. multilocularis in both municipalities. Restricting the analysis to environmental fecal samples containing a minimal quantity of host DNA yielded a prevalence estimate closer to that obtained from necropsy.