The role of rodents in the transmission of Echinococcus multilocularis and other tapeworms in a low endemic area

Sammanfattning: Echinococcus multilocularis is zoonotic tapeworm in the Taeniidae family with a two part lifecycle involving a canid definitive host and a rodent intermediate host. The work of this thesis followed the first identification E. multilocularis in Sweden in 2011 in a red fox (Vulpes vulpes). The main purpose was to describe the importance of the rodents for E. multilocularis transmission in Sweden. Echinococcus multilocularis was identified in both the water vole (Arvicola amphibius) and the field vole (Microtus agrestis), but not the bank vole (Myodes glareolus) or mice (Apodemus spp). As the number of E. multilocularis positive rodents was low (n=9), the examination of other taeniid parasites was used to investigate overall parasite transmission patterns. Rodents caught in field habitat (field voles and water voles) were ten times more likely to be parasitized than rodents caught in forest habitat (bank voles and mice). These results provide further support for the importance of field- and water voles found in field habitat for cestode transmission. Still, these rodent species differ from the most common rodent intermediate hosts in central Europe, and metacestode development within these species may be limited. Thus, the presence of E. multilocularis in Sweden could be constrained by the lack of an ideal intermediate host. The distribution E. multilocularis was found to be highly aggregated with localized areas of high parasite egg contamination. Despite an extremely low national prevalence, multiple positive rodents and feces were identified in areas with known and unknown E. multilocularis status. This success is credited to the targeted sampling strategy, which was designed to focus collection efforts in areas where risk for parasite presence was estimated to be highest. This sampling strategy could be used as a basis for future risk-based sampling to detect E. multilocularis in areas where parasite prevalence is low or unknown.