Support for targeted sampling of red fox (Vulpes vulpes) feces in Sweden: a method to improve the probability of finding Echinococcus multilocularis

Andrea L. Miller, Gert E. Olsson, Sofia Sollenberg, Moa Skarin, Helene Wahlström, Johan Höglund

Localized concentrations of Echinococcus multilocularis eggs from feces of infected red fox (Vulpes vulpes) can create areas of higher transmission risk for rodent hosts and possibly also for humans; therefore, identification of these areas is important. However, in a low prevalence environment, such as Sweden, these areas could be easily overlooked. As part of a project investigating the role of different rodents in the epidemiology of E. multilocularis in Sweden, fox feces were collected seasonally from rodent trapping sites in two regions with known parasite status and in two regions with unknown parasite status, 2013-2015. The aim was to evaluate background contamination in rodent trapping sites from parasite eggs in these regions. To maximize the likelihood of finding fox feces positive for the parasite, fecal collection was focused in habitats with the assumed presence of suitable rodent intermediate hosts (i.e. targeted sampling). Parasite eggs were isolated from feces through sieving-flotation, and parasite species were then confirmed using PCR and sequencing. Most samples were collected in the late winter/early spring and in open fields where both Arvicola amphibius and Microtus agrestis were captured. Fox feces positive for E. multilocularis (41/714) were found within 1-3 field collection sites within each of the four regions. The overall proportion of positive samples was low (≤5.4%) in three regions, but was significantly higher in one region (22.5%, P < 0.001). There was not a significant difference between seasons or years. Compared to previous national screenings, our sampling strategy identified multiple E. multilocularis positive feces in all four regions, including the two regions with previously unknown parasite status. These results further suggest that the distribution of E. multilocularis is highly aggregated in the environment and provide support for further development of a targeted sampling strategy. Our results show that it was possible to identify new areas of high contamination in low endemic environments. After further elaboration, such a strategy may be particularly useful for countries designing surveillance to document freedom from disease.